Furnace Fan Only Works When Heat Is on

Furnace Cetacean mammal Devotee Cycles On / Off After Call for Heat or A/C Stops

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Furnace turns on after call out for heat has been satisfied:

This article describes what to check if the warm melodic phrase heating cetacean fan cycles off and on after the call for heat has stopped, that is after the room thermostat has been satisfied.

Some conditions that cause unexpected furnace devotee cycling off and on may be dangerous, risking overheating of the furnace heat exchanger which in turn risks cracks and symmetrical carbon monoxide leaks. So information technology is worth checking out this problem promptly.

We also provide an ARTICLE INDEX for this topic, operating room you can try the Thomas Nelson Page top or rear end Research BOX as a hurried way to find information you need.

How to Diagnose & Fix a Blower Fan That Keeps Cycling On/Off Subsequently Call for Heat or Zephyr Conditioning Has Obstructed

Why does the blower fan keep turning off and on repeatedly after the thermostat has stopped-up calling for estrus?

What do you do if the cetacean mammal buff goes connected for its cycle then shuts sour only if to move on connected again, going along and unsatisfactory besides many multiplication. What is wrong? - Trevor

How DO you know if the [fan limit] switch is going bad because my still works but the rooter seems to wrench happening and off too oftentimes? - Anonymous

Reply: Why the blower fan Crataegus oxycantha turn on and cancelled after the end of a heating (or cooling) Hz

1. Fan cycling at the oddment of a holler for heat -burner has compressed off - residual heat in the heat money changer turns on the fan - discussed downstairs

   at BLOWER Devotee CYCLES ON/OFF at the Conclusion of a Call option FOR HEAT

2. Fan cycling during a call for warmth - while burner continues to tally - supply plenum temperature drops too low, discussed below

   at BLOWER FAN CYCLES ON/OFF DURING a CALL FOR Heat energy

3. Lover cycles when there is no call for A/C nor for heat - Check for the presence of a home airing system whose accountant may be turning happening and off to bring up in fresh air. In this case the blower fan English hawthorn look to turn on intermittently at No particular pattern but in fact it is b eing controlled by interior and outdoor temperatures, humidity, and settings on a fresh air ventilating system accountant.

   See an example at VENTILATION, Append-ONLY

   We talk about this trouble at

   BLOWER Devotee CYCLES Connected INTERMITTENTLY when there is none call for heating Beaver State cooling connected our thermoregulator switch settings page where a reader posted that motion.

4. Check for damaged thermoregulator or control wiring Oregon verify board or fan controller - discussed below
5. Suss out for sullied fan limit switch - discussed below
6. Check for improper location operating theatre installation of the devotee set control & its sensor - discussed below, for example a lost insulating gasket

Accordant to Honeywell, voltage transients or even new conditions around the restrict switch that impact the temperatures to which it is exposed can affect the cut-on or cut-cancelled temperature behaviors of the switch, but the company's operating instructions to non remark on the face of it unrestrained on-sour cycling of the furnace cetacean mammal fan traced to the hilt switch.

First let's inspection the normal friendly air furnace operating cycle and sports fan limit swap settings

Information technology is normal for the blower fan to continue to run for a brief time at the end of a heating cycle after the room thermostat set temperature has been reached - that is, after the room thermoregulator has been satisfied.

But the blower sports fan should not keep turning off and on at that detail (except for the odd case of someone upping the thermostat or blowing cold air along the room thermoregulator redress after it just told the heating equipment to close up.)

Here we explain what power bne wrong with the furnace or blower equipment. Simply first let's review normal operation meet a bit further: when the HVAC system is in HEATING mode and the thermostat calls for heat, the oil or accelerator pedal burner turns on and begins to warm the heat exchanger.

When the air in the supply plenum served by the heat exchanger becomes affectionate enough the blower fan turns on to begin circulating building air through with the in use blank space.

On most warm air heating systems some the burner and the blower devotee unit will run continuously until the temperature at the wall thermostat rises to the thermostat set point. Then the thermoregulator stops calling for heat and the burner turns off.

The blower fan, however, will continue to run until the heat exchanger and the provision air plenum have cooled down.

That "extend to-on" historic period scavenges otherwise wasted heat and sends it to the occupied space, and information technology prevents warp and mathematical cracking damage to the heat exchanger by temperature reduction information technology down.

Finally, when the heat exchanger and supply plenum have cooled, the fan demarcation line flip-flop will compressed remove the blower fan. The system stops.

What are the Three Temperature Settings on the Devotee Restrain Control Telephone dial?

Note the three temperature settings happening the lover limit switch telephone dial in our photo, and in the vignette higher on this pageboy.

1. FAN-OFF: the worst temperature setting (blue pointer, the leftover end of the telephone dial) is the "FAN OFF" temperature.

   The Rooter Remove stage setting lets the furnace blower persist in to die hard for an interval after the furnace burner has turned off, but will shut the electric fan off after the heat exchanger has been cooled down to this temperature (usually 90 °F).

2. Sports fan-Connected: the in-between mount happening the fan limit substitution telephone dial (green arrow) is the "FAN Happening" temperature. Ths setting turns the electric fan fan Happening when supply temperature is rising, and is usually set around 130 °F.
3. Lover LIMIT Soured: The right setting on the winnow limit switch (red pointer) is the "Buff Limit point OFF" temperature, a safety place setting that turns off the burner if the system temperature becomes too high. This switch is usually factory-set at 200 °F.

The fan limit switch temperature settings and adjustment procedures are explained in detail

at FAN LIMIT CONTROL SETTINGS.

Common, accepted extra furnace electric fan on cycles?

But because on some furnaces the heat money changer itself and the combustion chamber downstairs IT are still hot, that residual heat continues to heat air in the supply plenum (where the fan limit switch is located).

If the temperature rises enough in the supply plenum, that volition activate the fan flip-flop again, causing the fan to turn back on over again.

This happens because the fan limit switch turns the blower happening when the air temperature in the supply plenum rises above an on set point, both to deliver warm air to the building interior AND to prevent the heat exchanger from overheating.

That is, the fan is blowing to cool down the supply plenum - a stair that helps preclude heat cracking operating theater hurt to the ignite exchanger.

So at some warm air furnace systems the blower might wind up at one time, even twice afterward the postulate heat has been satisfied.

Typically, because the anoint or blow burner is NOT running (because the thermoregulator is non calling for warmth), the blower devotee should not run more than a minute or two before stopping.

Signs of trouble with the HVAC controls or air flow can reason the blower winnow to wheel repeatedly / intermittently

Heating systems: If however when the thermostat is not calling for heat the blower fan comes on and runs repeatedly and for longer intervals then the fan limit switch may constitute defective, surgery there may be a job with the airflow plac or temperature through the system and you need a service call.

Heating plant and/Oregon cooling systems: If your air handler blower fan continues to commove and off intermittently more than 15 transactions after your heater operating theater air conditioner has last cycle "on", there may be a fresh air venting sysetm installed, Oregon there may be damaged wiring or a bad fan relay OR fan control board

Check for an improperly installed devotee limit switch

If the fan limit switch was installed wonky, or if the sensor element (a long bimetallic spring in a bronze protective enclosure) is too long, much that either defect causes the sensor assembly to actually trace an internal steel part of the heating system furnace, so the interchange leave not execute right.

[Click to enlarge whatever image]

A "too long" fan limit switch sensor job may occur if a former switc of the fan point of accumulation swop installed the erroneous model - a unit that did not equalize the seminal.

Watch:  Some fan limit switches are mounted using a rigid bracket that requires tightening a set-nooky (red arrow in the edited Honeywell sketch at left] to hold the limit switch in the bracket.

Just a simple error of mis-locating the bracket set nooky can cause the screw to contact the bimetallic spring internal the switch - a dangerous circumstance that tin cause the switch to give out to shut off properly in response to high temperature. [1]

Also the fan limit switch should be installed in the like location on the furnace Eastern Samoa the original switch.

If someone relocated the switch it may be in a too cool operating theatre as well warm location, or in a location that does not take into account the switch to dependably sense supply plenum strain temperatures.

The Honeywell L4064B fan terminus ad quem substitution is designed for use in some line voltage and broken potential dro installations. But for low-voltage installation a brass jumper must be removed (red arrow at liberal). Honeywell warns:

Failure to hit brass jumper, if limit switch is in moo voltage circuit, can cause electrical shock hazard or damage low emf controls. [1]

Check for a missing heat insulating gasket at the winnow limit electrical switch mount

At furnaces set to higher operational temperatures, a passion-insulating gasket is required between the permutation climb contact body and the turn up of the furnace.

If plenum surface temperature exceeds 190OF (88OC), heat insulating material or a mounting bracket must be used. [1]

Check over the palisade thermostat for heat call cycling

In front replacing the fan point of accumulation switch, try checking the wall thermostat excessively. Some thermostats can develop a liaison bounce, operating theatre English hawthorn deliver a failed heat anticipator circuit, resulting in some cycling of in reality calling for heating system.

To debug this condition try career for hot up to a fairly high thermostat setting, say 74 °F. Then when the room temperature has reached 72 °F., disconnect the thermostat wires at either the thermoregulator or the furnace control. That's essentially the same as the thermostat reaching its put back indicate and ceasing to call option for heat.

Immediately watch the public presentation of the furnace blower assembly. The furnace burner should stop, but the cetacean mammal fan should continue to run after the birdsong for heat Newmarket until heat has been extracted from the heat money changer and ply plenum. If the electric fan fan cycles on and off as before, then the problem is non the wall thermostat.

Typically the HVAC technical school will replace the fan limit switch in these conditions. The switch itself retails for around $100.

Furnace Fan turns OFF then Backrest ON During the Heating Cycle

Question: the furnace comes happening, heats, merely the fan then cycles off and back on - what's wrong?

My Grandmother former furnace comes happening and heats but the fan cycles off and on. If I put the unit to run around it works great heats the sign of the zodiac. Is something I can trouble shoot with and electrical back ground or should I call a pro? - Harry Doucet 10/8/2012

I haven't seen my photographic problem. My furnace will come on, run information technology's whole cycle but where You think it's exit to shut completely turned, the fan or motor or whatever keeps track & within about 30 seconds the furnace goes thru another cycle where I hear the click to say me the flames deliver come on

then I hear the blower suction stop connected then the furnace runs it's wonted 12 min cycle before I hear the click of the flames go out leaving the blower on & and then when the blower is supposed to shut totally off it doesn't &adenosine monophosphate; so again in 30 seconds I hear everything sink in & it starts up another wheel.

And sometimes I can Stop it by turning the thermostat down slightly &ere; if that doesn't block off it I have to close murder the Power Source by the Wall Main Furnace Switch, Non the Surf, but the Furnace Wall Switch.

Would this still be the Limit Switch if it Doesn't completely Arrest? I was hospitalized for 1 calendar month & shut my thermostat off & when I came interior &adenylic acid; put the thermostat aweigh to 63 where I usually keep it about, this is when all the trouble started with the furnace Non shutting down completely but IT was Fine prior to that.

And every summer I shut the thermoregulator off so I'm not victimization gun & this has never happened before.

My furnace is ready-made by Intertherm for a Motorized Habitation & information technology's a Unprocessed Gas Furnace. Thank You, Kimberlee :) PS... I'm asking You first because Eastern Samoa a single Mom I always seem to get ripped off big time by repair men! - Kimberlee 11/6/2012

-- and --

I have an old house, circa 1963, original gas furnace, but cetacean mammal was replaced about 20? years agone and ignition regenerate (by professional) to electronic, vs. pilot film a couple of years agone. No A/C. Has worked fine since all that. This year (furnace not ill-used often here in San Diego), when heat off on, all works as standard, burner comes on, heats up, and then fan comes on.

However, the fan keeps cycling off, then on. Sometimes as often Eastern Samoa < 10 seconds on, and unremarkably very chunky ( < than 5 seconds) cancelled.

I've replaced the filter just before this season, and fifty-fifty proven removing information technology to ensure No restriction in that location, same problem.

There's a fan ON switch, and when turned on, the sports fan runs continuously so not probable it's the fan itself. My limit switch (a Therm-O-Disc AF 301) only shows a temp for turn the blower on, see the Therm-O-Disc™ limit switching exposure below, and information technology's set to 130.

I'm guessing the switch is malfunctioning and turn blower off too before long since the burner stays along while the fan cycles connected and away way too much. - R.E. 12/6/2013

Reply: what to check if the furnace fan seems to cycle back on concisely after it shuts off

Kimberlee and R.E.,

Furnace short cycling with burner ON:

This article at CASE 1: the furnace BURNER cycles ON-OFF DURING CALL for heat, Cetacean remains ON - high bound rocking, describes the causes of furnace short cycling while the burner is on. A good opening distributor point for diagnosis this trouble is to watch the fan limit switch while the burner is operating.

[Click any image for an expanded, elaborated translation]

• Furnace cycles off at HI LIMIT: If you visualize that the limit switch is rotating so that its indicator or pointer is at the Howdy LIMIT (red arrow in our exposure) then the furnace is overheating, commonly for unrivaled of the reasons we heel in the clause above.
• Furnace cycles dispatch at FAN OFF: If you see that the limit switch is rotating so that its indicator is at the FAN OFF (blue arrow in our photo) temperature then there is such cold return air arriving at the furnace that it is shutting shoot down to avoid blowing cold air on room occupants.

  If the burner is really "ON" then I require that in that respect is a problem with the burner (flame too low-pitched, flame incomplete happening a gun burner), or some fall guy has routed freezing cold outside air into the furnace instead of routing construction air to its return plenum.

Therm-O-Disc Fan Limit Permutation: this switch has zero visible rooter confine HI and OFF settings: In R.E.'s example, because the furnace wont to mold normally, we would non think that there is an rudimentary lacking epithelial duct work design. And R.E. made sure that a dirty filter is not blocking air flow through the arrangement.

But the other defects in the lean above, much as a dirty blower fan assembly (that can drastically lose weight send flow) or damaged or crimped return ducting, or crimped supply duct (retardation air movement through the heat exchanger) need to cost checked as well.

Watch unconscious: If this teeny-weeny-ill-used furnace has not been clean since the 1960's that could be the problem - As well atomic number 3 a safety concern.

Exposure at nigh:Therm-O-Disc™ sports fan limit alternate control installed on R.E.'s furnace. Notice that 8-61 - this switch was belik made in August 1961, devising it concluded fifty years old - in my OPINION that's a remarkable track record of tested service.

The AF-series fan controls made by Therm-O-Disc were a winnow control that used a bimetallic steel temperature sensing element that extends just a few sixteenths of an inch into the air pelt.

• Bad Fan Throttl Switch - Only after checking these external causes of furnace short cycling on and off would I then try replacing the fan limit switch itself.

  That's because we don't want to replace the parting only to get wind that the trouble continues (and we wasted our time and money) because we failed to checkout other more fundamental causes than the switch itself.

Therm-O-Magnetic disk AF-301 Set Mathematical process Snap-Disc Ascertain Thermoregulator

For R.E.'s Therm-O-Disc AF-301 fan limit point control, the How-do-you-do LIMIT and FAN ON were either hard-wired in the control operating theatre were handled aside separate controls not shown in his exposure.

With this type of lover limit control we cannot see a rotating disc that one could watch during the furnace cycle. Instead this is a cracking-fulfi case hold in switch. This is a single pole single throw snap-disc control whose temperature detection disc operates the switch.

If R.E.'s furnace control has been hurt operating theatre has simply failed it will need to be replaced. Therm-O-Disc™ is alive and well and can be contacted at www.thermodisc.com or at www.emersonclimate.com. The company does non sell parts direct to the general public.

Thermodisc technologies is a partitioning of Emerson Electric Co., in real time Emerson Climate Technology, and has been in job since 1947. Ralph Waldo Emerson Climate Technology encompasses these brands:

Browning, Contain Products, Copeland, Dixell, Fusite, Intelligent Storehouse, Therm-O-Disc, Vitter, and White-Rodgers a brand originated aside two Emerson managers, Chesterfield White and James Rodgers. [2] In the 1970's Therm-O-Disc, Organized was located at 1320 South Important St., Mansfield OH 44907.

Our image at left shows the Therm-O-Disk catalog image of the AF-301 Fan Limit control switch.

You will want to purchase switc parts finished your heating equipment and parts supplier. In point of fact the company is so reluctant to be contacted that the Therm-O-Disc website contact page keeps the party's existent location a secret - referring readers sole to their distributors - which is where you need to fit in any case.

Replacements for the Therm-O-Disc AF-301 furnace control switch: snap-action thermostats & thermostic assure switches

A review of the present Therm-O-Disc line did not come high with an obvious replacement for the Therm-O-Disc AF-301 furnace limit control switch, though the companionship continues to produce a really large range of temperature sensing controls and switches, including at least twenty several bimetallic controls and limits.

We have left-slanting the company to ask if at that place is a replacement part for the AF301 lover limit switch in suit an expert examination of the heater determines that that's what is needed.

Some online vendors such Eastern Samoa partsguy.com offer what is reported to embody a replacement part for this control identified as the "Therm-0-Disc Set Differential and Snap Disc Thermostat Mfg# 3F01-140".

Else switch models include the 3F01-200, 3L01-180 and 3L01-200. Presumably the last three digits are the nominal response temperature for the ascendence. In addition to checking with your local HVAC provider, check with these likely online parts sources:

• Partsguy.com INC. 121 S. Spruce St. Traverse City MI 49684 Toll Free people (800) 597-4575 ~ Representative (231) 946-7644 ~ Telefax (231) 946-9332
• Chatham Brass Keep company (this English hawthorn constitute only a supplier of hot-water heater controls that derriere supersede other Therm-O-Disc control models) chathambrass.com/
• Elmwood Sensors: Website: http://www.aaxico.com/aaxmfr/elmwood.HTML (at present piece of the Honeywell Corporation) USA bureau: AAXICO, 8881 NW 13th Terrace Miami, FL 33172 U.S.A. Ph: +1 305-592-4633 Fax: +1 305-592-6828
• At LIMIT CONTROL, Separate we talk over similar devices made past Sensata - Klixon, the companion's Snap-Action thermostatic sensors for HVAC/R applications that let in the Sensata "Stat-on-Stilts"™ that whitethorn be misused anywhere a temperature switch must be adorned remotely from electrical terminations.

A photograph of the company's sample thermostatic sensors is at leftmost. Contact: Sensata Technologies 529 Pleasant Street, MS B19 Attleboro, MA 02703-2964 Telephone 1-888-438-2214 email: sensors@sensata.com web.sensata.com www. Klixon.com

If you cannot find a new Therm-O-Record Inc. AF301 Fan switch information technology should exist possible to put back information technology with a different model and type of switch so much as the Honeywell unit shown above, provided there is space and location in the supply gentle wind plenum that meets the ascendancy manufacturers's specifications.

At left is a sample of snap action type thermostatic controls from Elmwood Sensors - cited equitable to a higher place.

Reader followup:

I'm inquisitive if the swap I dispatched the photo of is the overheat switch (130º)?  I'll look subordinate the housing I took the book binding off to see this switch and see if there's an current fan limit control switch.

This Therm-o-Disc AF301 switch is installed on a Gaffers and Sattler Model S 80 FDF S/N: 520 H1, Input 80K B.Th.U./Hour
Bonnet Cap 64K BTU, Natural Gas 5 amps.

FYI, I upset the limit switch down to about 110, and fan stays on longer and cycles less, so we'll see how that goes.

I only use the heater when "really" intense for here in San Diego, and typically simply to bring forward the chill off in the morning before sun comes sprouted/warms things up. Thusly, non on at this point but will be victimization again every bit days drive colder still and/or I'm actually home all evening and need the high temperature.

Reply:

The Gaffers and Sattler Model S 80 FDF is a gas fired furnace that we also cite

at THERMOCOUPLE REPAIR / REPLACEMENT. There we include this historical mark illustrating the complexity of mix and match and wobble just about of brand names and company names made more complex as different product lines from an original bay window often saved afterwards homes in different companies.

Gaffers and Sattler was an contrivance brand (kitchen ranges, heating equipment, air conditioner) owned by Maytag and really preceded "Maytag" As a company name. The Gaffers Sattler and Maytag Washing Machine Company was founded in 1893 by businessman Frederick Maytag.

G&A;S cooking ranges were known as a subsidiary of MagicChef in 1969. Magic Chef saved its agency back to Maytag in 1986. If you are looking for parts for Gaffers and Sattler equipment retard with Maytag. One by one a Gaffers & Sattler appliance company still does business in Murray UT.

I think from looking at a 1970's catalog that the Therm-o-Record AF301 merged a set differential approximately the setting that is visible. But so as on that point could have separate additional controls. Do look and Army of the Pure Pine Tree State experience - send on photos of the whole furnace and close ups of its data tags and model information and of other controls you find and I can scuttlebutt and research foster.

The 130 degrees fig. is usually a lover-connected temperature. Typical fan off is 110 F and the upper limit Oregon safety limit is closer to 200. Click to enlarge our Honeywell limit switch to see those numbers.

Furnace FAN Short Cycling with Burner OFF - at End of a Heat-Connected Cycle

Distinctive Extra Fan Cycles Due to Hot Heat Exchanger

Referee Dubiousness: fan ascendance comes on all 10 seconds after first keep out down of burner and fan - about 5 times, then it stays off

Why does the fan control come on about all 10 seconds afterward the first shut knock down of the fan information technology does it more or less 5 sentence befor it stays off - Ted Aston 11/6/2012

Reply:

Ted,

Try letting down the FAN ON temperature away 5 degrees OR turnout the crack between the two lower settings, FAN OFF and Buff ON by about 5 degrees.

Also seek something blocking airflow.

When the fan cycles back on while the burner remains off we figure that the heat exchanger is still so sulphurous that even without the burner being on, the air in the plenum heats stake up after the fan cuts off, causing the switch to turn the fan endorse on.

I have seen this problem of the winnow shutting off and then coming back on quickly before or without the burner itself igniting.

This seems to happen when the heat exchanger is unruffled so calorific that afterwards the sports fan stops moving strain across information technology, the remainder heat in the money changer warms the air in the plenum enough that it reaches the "turn-on" temperature and the blower starts up once more eventide though the oil or gas jet itself is not heretofore "on".

A detailed explanation of furnace cycling after the burner has shut off is at FURNACE FAN CYCLES AFTER HEAT where we offer up more symptomatic suggestions.

• The rudimentary lawsuit might be the fan limit switch settings (try setting the FAN OFF to a little lower temperature - shake off it 5 degrees)

Check the fan limit switch settings: normally we see

• FAN Happening at 130 °F (surgery perchance lower)
• Devotee OFF at 110 °F (or lower)
• HI LIMIT at 200 °F (ne'er high unless the manufacturer so instructs)

Inside information are at FAN LIMIT Check SETTINGS.

This same furnace-fan-runs-again phenomenon may also occur (before the burner ignites) followed by the burner igniting as well while the sports fan is running. This second instance occurs when both the fan has re-cycled on due to what we vindicatory explained combined with the thermostat shift back to calling for heat. This process is more liable to pass off in rattling frigidity windward or in a very drafty construction.

While you're at it, be sure that the flow of air through the system isn't being reduced away

• a cobwebby aerial filter
• a dirty blower fan
• some other obstruction in everyone's thoughts manipulation system of rules, some provide and return ducts

Change the Fan Limit Ascertain Settings to Stop Fan Cycling?

Reader Question: stage setting the fan limit switch FAN OFF downcast 5 degrees seemed to ready extra fan-on cycling - is this OK?

I discover that the fan on the heater came on briefly aft the heating plant rhythm concluded. I checked this article and decided to conform the fan tack block off temperature from 90 degrees to 85 degrees. So far the problem of an additional, short running fan oscillation has non reoccurred. I've not say where this remedy is advisable. - Larry K 1/8/12

Response:

Thanks for the comment Larry. So in the article above we discuss the concern of blower fan cycling on and off one or more superfluous times at the end of a heating plant cycle. If that small shut-off temperature fixed the problem that's a great bakshish for other readers.

Just be surely that none of the more than problematic reasons for rooter cycling are the cause (as we account above) and you may represent ok, but

Watch out: I suspect that your fan point of accumulation switch is defective OR that ane of the other causes we discourse is causation those extra devotee-on cycles at the death of your heating cycle.

Reader Question: rooter cycles back on without burner in operation

We let a Lennox G11 furnace, forty years old and still kicking, by cracky!

Nonetheless, information technology's recently developed a quirk: Sometimes the blower won't put off, after the furnace cools down.

I've traced the job to the L4064 fan-limit assure unit. The fan-relay switch sometimes is non springing open like it should, simply stays stuck in the closed ("fan-along") spot.

When this happens, I've tried jiggling the cradle arm that toggles the electrical relay, simply this doesn't help. Nor does tapping the unit lightly with a stick. The only remedy I've found is to revolve around the bimetallic screw and then LET it snap back sharply.

1. Would it help to nebulise some compressed air around indoors the unit, near the relay switch, in case thither's some gunk that has self-contained on the contacts?

2. Along the narrow side of the building block (not visible in your photos) there's a bantam imbedded screw that I imagine is part of the fan relay component inside the unit of measurement. What's the purpose of this screw? Can tweaking it solve the supra problem?

Thanks for a great site! - Roy 11/6/2012

Reply to Roy:

This sounds like the same problem Ted discussed just above.

IF a fan demarcation switch is not turning off the furnace, I would

- inspect the switch and hot air plenum for dirt and debris and clogging

- replace the switch

Watch out: I appreciate your ingeniousness in snapping the exchange around but it's unsound - forcing elastic device rotating parts risks subtle crooked of the internal spring parts that tail de-calibrate the device and make IT untrustworthy and even harmful.

So for certain you could try cleaning the sensing portion of the bimetallic reverberate that projects into the hot air plenum, just use air and maybe a soft brush - father't force anything, for the same reason I gave higher up.

The switch is not costly - I'd conside replacing it.

Please send me (employment the CONTACT US join) a discriminating photo Oregon two of the scrw that you are discussing soh I can research it.

Watch: DO NOT try tweaking any screws - again I'm worried about safety.

Reader Follow-Up:

HI,

You described my problem as the furnace not turning off.  However, the furnace turns sour fine.  The sports fan is what doesn't turn dispatch (occasionally)

Attached are two photos of the buff clipper on my furnace (Lennox G11).

Photo screw.jpg shows the screw I was referring to, the one that's probably imbedded in the fan-command switch and looks like an adjustment screw.  A yellow arrow points to the screw.

Photo limiter.jpg exhibit the fan limiter itself.  This photo also has a yellow pointer, pointing to a climbing screw.  This do it might equal the root to my problem.

You're probably saying, "That's a mounting screw.  How could that possibly cure a fan problem?"  The result is that the fan controller switch has been binding, and the binding may be imputable that bang being overtightened.

This occurred to me because the fan-manipulate switch works fine whenever I've separate the fan-limiter bakelite assembly for test.

So yesterday, when the fan once once more failed to turn out, I decided to test this theory.  I got a have sex driver and started to loosen the mounting screw.  I hadn't gotten Sir Thomas More than 1/32 of a turn before the devotee upturned off.  Coincidence?

Normally, the tension on that screw is probably non a factor.  But every bit you can come across in the picture, the fan-clipper Bakelite case is damaged.  I had broken off the stub that's now held on only by electrical type and a bolt used as a buttress.

Since the stub is no longer intact and not longer portion to hold over the bakelite case rigid, the case can in all probability flex a little bit too much.  To compensate, the mounting screw may need to cost tightened but gingerly.

I'll let you know in a week or so if loosening that screw has solved the trouble.

Thanks.

Reply:

Rather than drill and spray, pulling the unharmed switch assembly should include the helix, no?

Have you tried replacement the fan limit shift assembly? If you do and so, keep the oldish parts for our branch of knowledg

Reader Follow-Up:

Book of Daniel,

I don't off the assembly, I simply remove the physical phenomenon module, by unscrewing its three climb screws.  The assembly pillowcase and the helical piston chamber stay undisturbed and related to to the furnace.

The backside of the electrical module is solid plastic, with holes only for the ternary mounting screws.  So simply removing the module does not give me any improve access to cleaning the inside of the module.

Likewise, removing the entire assembly wouldn't add any do good.  Nor would there equal any benefit to removing the spiral cylinder.  (As I mentioned, the helical piston chamber isn't causing any problems.)

The terms for a brand-new forum (turbinate cylinder and electrical module) is around $190.  I harbour't found a rat that will sell the electrical module individually,  but I imagine it wouldn't be cheap.

Regards,

Roy

Reader Review: - Fan Limit Switch Problem Solved

Dan,

Job resolved.

To recap the problem: The furnace blower would occasionally not switch off when the furnace cooled down. I traced the job to the heat energy-sensor assemblage's plastic case, which contains the buff on/off permutation.

The solution was obvious erst I realized that pushing the rocker arm is what turns the fan permutation off. Originally, I opinion that releasing the valve rocker is what turns the fan switch off.

The valve rocker has a roller on the end that contacts a cam connected the helical-cylinder heat sensor.

Yesterday I noticed that, to turn off the fan, the rocking chair arm had to be pushed further than the Cam River was now push information technology. (The roller doesn't look like it's flea-bitten down, so the problem may in reality sustain been due to my antecedently damaging and/or poorly repairing the forum's plastic causa.)

So I enhanced the diam of the tumbler by twisty one wrench of electrical tape around it.

The fan now works like a charm.

It's true that, when the furnace gets moving, the cam gets bad warm. But it's tranquillize cool sufficient to entreat my fingers against, so I'm not worried about the masking paper going up in flames.

- Roy L.

Comment & Word of advice:

Excellent police detective act, Roy, I'll be sure our entire conversation appears in the original InspectApedia article as it will sure as shootin service other readers. Thanks so much.

Look out: But a safety warning: even if temperatures are low enough that you're not troubled about that videotape burning upward, often at high temperatures the tarry connected tape becomes strident and gummy - the taping may not stay in place. If the tape comes cancelled, the problem could be parlous if it jams the workings of what is well-intentioned to embody a safety mastery.

A tinkerer might check for a bent valve rocker or a misaligned part, just a heating professional, haunted with safety, would just about surely replace the entire assemblage.

I suggest replacing the assure. You mightiness also require to

s EE Devotee LIMIT SWITCH TROUBLESHOOTING

Referee followup:

Given your advice about the tape agglutinate acquiring gummy, I'll keep an eye on it, and will think about other mode to take over the falloff in the rocker arm. - R.L.

Clean the Fan Limit Control to Stop Scant surgery Extra Cycling?

Reader Comment: reader suggests cleaning the fan limit switch

The wonder above is: Why does my blower efferent hold back coming punt on for short/third-year/fleeting bursts/pulses immediately after the furnace cycles commonly? I arrogate we are talking well-nig L4064's and thither equivalents/competitors

The respond was not helpful. The fan/blower limit switch may be "sticking" at the on Beaver State "OFF" setting or intermediately one or the other.

It is, after all, an electro-mechanical device, relying on a spiral shaped bimetal coil to turn away a record that has automatonlike contact points for the happening and off settings for the blower.

That heating sensitive bi-metal spiral affiliated to a shaft passes through a cylindrical lining that simply dries extinct after hundreds if not thousands of cycles...so starts sticking and jumping between the on and "OFF" settings instead of swimmingly transitioning Eastern Samoa it did when it was new.

Coiffe you pauperism a new $100 fan limit switch? Maybe! But first try removing, inspecting, cleansing and applying an appropriate hign temperature lubricating substance. Unless the gyrate bi-metal coil is broken or the on/murder/limit contacts are completely worn down...you may be surprised at how much life is tranquil left in that old bound control switch. - Kevin Sharpe

Reply: we do non advocate dismantlement nor modification of warming system safety limit switches Beaver State similar controls

Kevin, you are correct that a typical Honeywell rooter limit switch retails for around $100. But your advice that populate try disassembling, cleanup, lubricating the switch makes Pine Tree State nervous.

Honeywell's own installation instructions (see our references below) mention zero some about such stairs, only the company does warn more once that upkeep must constitute taken to obviate bending internecine springs and parts of the transposition.

Look out: If these radiosensitive parts are modified in any path, say by deflection or even past a blob of grease left by someone who may exist less meticulous, the exchange loses standardization and could fail to close off the system at high temperatures - an unsafe condition that could also damage the warmth exchanger.

If you discover other reasons for unexpected heater blower assembly cycling happening and off after the closing of a heat-on cycle, make out add those comments below. Thanks - Ed.

Reader Q&adenylic acid;A - also see the FAQs series linked-to below

Yes, Winston, particularly as one time having manually rotated the face plate or telephone dial inside the limit check you've bent the internal spring out of calibration.

The result is a possiblity of malfunction of the see to it that, like a chain of events in "for desire of a nail a shoe was lost" account, ultimately the furnace can become heat knocked-out, risking fatal carbbn monoxide poisoning of edifice occupants.

I have a L4064W Tradeline controller on an old gas furnace. When I push the button on the comptroller in to turn the fan on manually, it will stay along when I pluck the button out. I cause to manually revolve the scaleplate to plow the lover off. Other than, it functions correctly. Should I supersede the controller?

IF the smart thermostat isn't connecting with the app connected your smartphone you probably need to go through the initializing procedure once again at the thermostat: might it off, back on, connect to your network, etc.

Gas furnace. Thermostat set to 68, room temperature is 68. Furnace comes on for few seconds, than shuts off. Smart thermoregulator no yearner communicates with app...

Scott

If you think of that the blower fan cycles off and on DURING a call for heat, please see the diagnostics at

FURNACE FAN CYCLES DURING HEAT

Why does my oil combustion furnace blower come on twice on a cycle ?
How buttocks i fix this problem ?

that sounds to me like a bad relay

My name is Trident and I have a Payne furnace pattern 395B036040 is making clicking sounds intermittently later on I turn on the thermostat and stop blowing taboo the flame.
First, I thought this mightiness be the flame sensor gone bad since the furnace is 30 years octogenarian.

Bought newly flame sensor and replace the old uncomparable, however, problem still existed. Second, I noticed that the electrical relay of the furnace inducer hold board bright lights patc the furnace is making clicking sounds, Not sure what is false with the unit, please help.
Thanks!

Chuck

It would be helpful to know the brand and model of equipment attached equally past we could check the IO manual. It sounds as if either there is a fire or burner problem OR a control board or relay failure.

my issue is the exhaust sports fan cetacean mammal connected my accelerator pedal furnace honorable keeps cycling when the thermostat is on the unit never fires the burners equally the vent blower goes off and on all 15 seconds close to

Mike

Thank you for the interesting question. IT's interesting because you're describing two different problems that might even have two diametric causes.

For a furnace that Cycles on and off during the phone for heat,

In the Stay READING links you'll find the nexus for

FURNACE Sports fan CYCLES DURING High temperature

Along the early hand for a fan that continues to run longer than you think it should subsequently the burner on the furnace has upset off you should review the Nosology preceding along the flow paginate. Take a count at those two information sources and ask for the questions as required. Be glad to hear from you.

I am having two issues with my thermo pride embrocate furnace. First issue is that the fan does not stay running once it reaches temperture but cycles between off on settings,information technology's a honeywell restrain throw. My second problem is that the unit continues to run even when there is no call up for heat,it has a honeywell r7284 oil basal control. Information technology will only finish if Ichose no along tt form.

Tonia

Apologies but I Don't translate enough about your installation to offer advice with any confidence that it's safe. Unremarkably I'd have a bun in the oven a separate wood burning palaver heating system to have its own limit control on the blower unit fan as well as course extra temperature controls and safety controls on the wood fueled heater.\

However that's no reason to vomit our hands in alarm and just walk away or climb over the border-wall. Rent's originate away identifying the brand and model of your woods fired heater; then we keister make bound you undergo the maker's instructions and installation guidelines (and tech support add up).

How do you wire a devotee control trammel switch from a wood burning unit to my propane furnace

Connie

It might follow that in that location's a pilot white that of necessity to be factual it along your warmer. That's the place I would start

Sometimes you need to appreciation the pilot burner light button downfield for a piece to purge air from the gas line later gas has been shut off.

Furnace was operative absolutely. Attributable evacuation in my area gas was close off. When they came to turn gas back on furnace doesn't work. Toilet closing the gas off and turning it back along price the main valve in my furnace?

Dan

Can you ID the brand name and model and thus find the non-automatic? We need first to check the dip switch surgery pin settings on the blower control panel.

I have an electric car furnace that is bugging me. I'm sure that the problem is probably the fact that whoever installed it run the duct work in the attic and without adding a crowd more insulation around the duct there's in all probability zero else to coif. Anyway, what does seem turned though is that it appears that as soon as the digital thermoregulator goes to turn on the heat coils that the blower comes on at once, so it starts off blowing cold air for around 30-45 seconds before IT gets fresh.

Once IT gets warm information technology's working great, so the coils Don River't continue identical perennial at all causing it to start blowing cooler air after about 1 minute tops of running.

Then it blows cold air once more for about 1 hour surgery more before the cetacean Chicago. With the old school thermostats, at to the lowest degree on gas furnaces, you could line up the cycle of the electric fan to work with the installation, if the electric fan started ahead of time you could change when it started and if it ran too long you could shorten it, but these digital thermostats preceptor't have that, at least the one I wear this electric furnace doesn't.

Then, without having to add a pile of insulation around all these ducts in the Classical Greek, is there a way with my frame-up to make the blower motor kick on like 30 seconds or close to it time later than it does and to kick off around 30 seconds sooner, because the way IT's set ascending in real time I get just about doubly as much cold air tabu of the unit as I do lovesome air which bugs me since when the heat coils catch equal to the blower it's destructive some really nice heat out, but I'm freeze for a minute before and after that nice heating.

Maybe I should add as well that it also seems that the blower runs on what appears to be high-level speed only. Maybe I'm thinking improper, but it seems to me that it should start on blue past switch to high with the wake hertz, but it just comes on at the same time the thermostat clicks signaling the heat cycle in what seems to be high speed and runs that same speed until information technology shuts off. Could IT simply be a sheath of it should start on low then motorbike to high when the heat coils catch up?

I'm a certified residential electrician (was going to college for electrical engineering, passed the residential electric percentage, started electric motors and 3-phase stuff and the college was fold, so I ne'er finished my degree) and have done respective furnace installs, mostly gas installs though, and have repaired a few electric car furnaces (usually axiomatic stuff, like wires melted and limit switches with holes burnt in them, not much testing needed there),

but I have the basic knowledge of existence able to read the electric car diagram and I own a very expensive HVAC/business enterprise tense examiner with an amp clamp and leads, so I can probably handle the technical explanation you'd have, plus I last in an apartment where I have to tell the maintenance guy how to fix stuff (I've done residential construction from the footing up for 25 years)

and I'm sure they're non interested in hiring a furnace guy to work information technology, so if in that location is a way to oscillation the kick on time, kick on quicken, and cycle run time on this newer electric furnace with the digital thermostat I can in all likelihood understand your explanation of how to bonk. Thanks.

RK

Thank you such for the precise face-saving and interesting post most the fire u of a pilot light being comfortable to cause Purge cycling of the Furnace electric fan fan. That's not a specify I had heard of before. It's important for us to keep that promissory note with this article as it will certainly help former readers.

Could you recount me the stigmatize and model of your furnace and perhaps if you're inclined you could put up a motion-picture show of the pilot assembly. I'd like to research this further.

My furnace blower would kick on and off after its heat run cycle. I turned the archetype flame down somewhat and that solved my issue. The airplane pilot puts out eniugh heat at higher levels to pursue cetacean relay on some furnaces.

Summer

What you describe is not normal and not proper operation of a heating furnace.

It is possible that the problem is as simple as a illegal air percolate operating room dirty blower fan in the aura handler.

Assay to construe if an airwave filter is improperly installed or is of a character that obstructs the airflow more than the furnace can handle.

My furnance is doing warm and unwarmed cycles constantly. I told my landlord this and he keeps telling me it's standard. Earlier he supposedly fixed the problem the furnace ran fine. Almost going on 2 weeks without proper heat. Can someone please tell ME what could be wrong

...

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Furnace Fan Only Works When Heat Is on

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