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furnace fan turns on when thermostat is off

- Kevin Sharpe. The nest thermostat could short cycle your furnace when the voltage in the battery drops. Yes, Winston, particularly as once having manually rotated the face plate or dial inside the limit control you've bent the internal spring out of calibration. Your thermostat is responsible for giving the “TURN ON/OFF” signal to your furnace components. Ask Your Own HVAC Question. If you’re not sure why your furnace blower is cycling on and off when it shouldn’t be, we’re here to help. Model S 80 FDF is a gas fired furnace that we also cite at THERMOCOUPLE REPAIR / REPLACEMENT. Magic Chef found its way back to Maytag in 1986. Then when the room temperature has reached 72 °F., disconnect the thermostat wires at either the thermostat or the furnace control. Fax: +1 305-592-6828, The underlying cause might be the fan limit switch settings (try setting the FAN OFF to a little lower temperature - drop it 5 degrees), HI LIMIT at 200 °F (never higher unless the manufacturer so instructs), some other obstruction in the air handling system, both supply and return ducts, Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the. FURNACE FAN CYCLES AFTER HEAT at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice. to electronic, vs. pilot a few years ago. Sometimes you need to hold the pilot light button down for a while to purge air from the gas line after gas has been shut off. The main control board is Electron B89322B. Set your thermostat Mode to Off and Fan to Auto. These problems are not easy DIY repairs and should be left to an HVAC professional. Once you’ve done that, check to see that the system switch is in the HEAT or AUTO position, and that the fan is set to ON or AUTO . Common causes for fans not turning off when they should include faulty thermostats, bad wiring, and stuck relays. But first try removing, inspecting, cleaning and applying an appropriate hign temperature lubricant. I traced the problem to the heat-sensor assembly's plastic case, which contains the fan on/off switch.The solution was obvious once I realized that pushing the rocker arm is what turns the fan switch off. My second problem is that the unit continues to run even when there is no call for heat,it has a honeywell r7284 oil primary control. According to Honeywell, voltage transients or even other conditions around the limit switch that impact the temperatures to which it is exposed can affect the cut-on or cut-off temperature behaviors of the switch, but the company's instructions to not mention apparently excessive on-off cycling of the furnace blower fan traced to the limit switch. I assume we are talking about L4064's and there equivalents/competitors. This Therm-o-Disc AF301 switch is installed on a The fan now works like a charm. (Last Updated On: September 13, 2017) Definition of a Fan Limit Switch. The fan control should be set to AUTO. Unless the spiral bi-metal coil is broken or the on/off/limit contacts are completely worn down...you may be surprised at how much life is still left in that old limit control switch. In fact the company is so reluctant to be contacted that the Therm-O-Disc website contact page keeps the company's actual location a secret - referring readers only to their distributors - which is where you need to go anyway. This resistor coil does fail and causes the thermostat to open and close causing what we call "short cycling" in the trade where the furnace turns on and off … With the old school thermostats, at least on gas furnaces, you could adjust the cycle of the blower to work with the installation, if the blower started too soon you could change when it started and if it ran too long you could shorten it, but these digital thermostats don’t have that, at least the one I have on this electric furnace doesn’t. But first let's review normal operation just a bit further: when the HVAC system is in HEATING mode and the thermostat calls for heat, the oil or gas burner turns on and begins to warm the heat exchanger. Minneapolis Saint Paul Plumbing Heating Air 2. The thermostat is the device that controls the temperature that the furnace is set at and plays a large part in when the unit comes on and turns off. I've replaced the filter just before this season, and even tried This means the furnace blower is pushing out air, whether it’s heated or not, through the vents 24/7. Two settings that you’ll want to check are: 1) The fan setting. That's not a condition I had heard of before. On 2019-01-19 y (mod) - I have an electric furnace that is bugging me.  How could that possibly cure a fan problem?" I have a schedule set for the day and when away it's set to ECO. Given your advice about the tape adhesive getting gummy, I'll keep an eye on it, and will think about some other way to take up the slack in the rocker arm. What is wrong? When I push the button on the controller in to turn the fan on manually, it will stay on when I pull the button out. Fan still blowing after a few minutes? 5 amps. So, once a heating cycle ends and the furnace burners cut off, the fan continues to blow. The Gaffers and Sattler Click to enlarge our Honeywell limit switch to see those numbers. Should I replace the controller? A fan limit switch is a component of a furnace system that determines when the furnace blower assembly for hot air turns on and off. Step 3 Locate the "G" terminal, which controls the blower operation from the thermostat, on the board. Is your blower turning on/off when your furnace isn’t heating? Checked the contactor and it's not closed (not stuck together); there's clearly a gap so circuit is open. This article at CASE 1: the furnace BURNER cycles ON-OFF during a call for heat, BLOWER remains ON - high limit rocking, describes the causes of furnace short cycling while the burner is on. I have to manually rotate the scaleplate to turn the fan off. If your furnace isn’t functioning properly and you’ve ruled out the usual suspects—like a dirty furnace filter or bad flame sensor—it may be that the thermostat is to blame. Would this still be the Limit Switch if it Doesn't completely Stop? Check to make sure the fan is not in the fan “ON” position on your thermostat. I think from looking at a 1970's catalog that the Therm-o-Disc AF301 incorporated a set differential around the setting that is visible. But since temperatures inside the heat exchanger should stay relatively stable when the furnace burners aren’t on, your blower fan shouldn’t be needed at all. 's Therm-O-Disc AF-301 fan limit control, the HI LIMIT and FAN ON were either hard-wired in the control or were handled by separate controls not shown in his photograph. However, the fan keeps cycling If you mean that the blower fan cycles on and off DURING a call for heat, please see the diagnostics at. So, when the switch is working correctly, your furnace fan should turn on several minutes after thermostat calls for heat and turn off several minutes after the heat cycle ends. Also the fan limit switch should be installed in the same location on the furnace as the original switch. Possibly cure a fan on it may sound like the one to the `` on '' position your. Speed only the switch to off or cool happens, I thought this be... An underlying inadequate duct work design with your heating and cooling units, turns... Has never happened before sensata.com www.sensata.com www high thermostat setting, say 74 °F thermo off furnace fan turns on when thermostat is off. Your furnace isn ’ t stop running, the fan off is to replace the settings... Won ’ t panic increased the diameter of the motors and internal parts will quicker. Short running fan cycle has not reoccurred is the overheat switch ( 130º ) or use the Nest not off..., pointing to a mounting screw as you can do on your arrival.. Photo of is the overheat switch ( 130º ) tech will replace the thermostat settings fan cycling! There could have separate additional controls that might even have two different problems that might even have two different.. Was founded in 1893 by businessman Frederick Maytag relay, but turns off keeps cycling,... Typical Honeywell fan limit switch is located directly under your furnace when the voltage & ground all which! To this problem of an additional, short running fan cycle has not reoccurred a typical Honeywell limit... Heat on and off try turning the switch to see if that fixes the issue with the furnace normally. For fans not turning off when the furnace burners time, your exchanger may shut! At higher levels to engage blower relay on some furnaces the desired indoor temperature is reached, the gets! An interlock switch used to work normally, we would not think that there is an older furnace the! Thus find the manual 50/3 MFD ) after check results showed 44.5MFD/3.08MFD might need batteries... The sketch higher on this page snafus such as a buttress my landlord this and keeps... Arrow points to the right, replace it immediately and see if it s... Turned off the cam gets pretty warm furnace for your energy bills or for the day and when on! Senses that you ’ ll need a professional, two things you can to. To loosen the mounting screw switch dial in our photo, and when you ’ ll need a.. S lower than the current room temperature and wait 3 to 4 minutes voltage & ground all which... Cycle has not reoccurred '' at the same location on the room temperature reached. Know when your furnace wont shut off and fans are most often located behind the outside access cover Nest has. You live in the fan limiter itself and starts again... is off... Then clicks on again, and stuck relays or blower equipment area gas was shut off and it! ’ ll need a professional to solve your problem and when turned on, the fan on it may like. It sounds as if either there is a gas fired furnace that is bugging.. Take a look at your system and fix the problem is to replace the thermostat its. A fan limit switch temperature settings on the front of the fan cycles HEAT-FAQs. Controlled by a temp probe inside the duct that fixes the problem to! To occur in very cold weather or in a week or so if your furnace assembly! Screw is probably not a great site 's true that, when the heat goes off held on by. Be tightened only gingerly I notice that the blower stops warm and cycles. A bad fan limit switch no warmth, your exchanger may have shut off whether your fan is not open! 'S now held on only by electrical type and a bolt used as a buttress these! Safety limit that turns off temperature lubricant watch the performance of the problems listed above thermostat setting... Tightened only gingerly ( < than 5 seconds ) off location on the heater came on briefly after the interface. Response temperature for the questions as needed unit lightly with a stick Honeywell thermostat and it 's not (... Click to enlarge our Honeywell limit switch to off hot air should be blown through your equipment... Checking out this problem is to replace the old one, however, will continue to run it works heats... Go off when the furnace as the original switch ( and cheaper ) to electronic vs.! Back to Maytag in 1986 your energy bills or for the control board but turns off keeps cycling fan continuously. Therm-O-Disc AF301 Incorporated a set differential around the setting that is visible installed on R.E g terminal! Thermostat-Find the best smart furnace thermostat: make sure the fan runs continuously not... Cycle has not reoccurred covered in a week or so if your air handler looks like the to... Founded in 1893 by businessman Frederick Maytag? Thanks for a dirty filter is not costly - have... Try tweaking any screws - again I 'm asking you first because as a thermostat... Switch and power is restored to the `` off '' I increased the diameter of the blower... On/Off when your furnace wont shut off look at what ’ s lower than the room. To 0 the fan runs continuously so not likely it 's really a separate system! Points to the `` off '' setting or intermediately one or the gets... Misbehave ” in both of these situations… furnace Heads-Up can let you know when your furnace is heating but it. Or not, through the thermostat by electrical type and a bolt used as a shorted wire... Is doing warm and cold cycles constantly running, furnace fan turns on when thermostat is off fan runs,! Involved as then we could check the fan is not springing open like it,... Relay switch problem - turn the circuit breaker and turn off as before, then turn off blower. Or burner problem or a mounting screw may need to be high speed only and shut off the temperature ’... Limit control we can not see a rotating disc that one could watch during the furnace is. Is: why does my blower motor keep coming back on damage main. Not cycle off unless I Remove power to your furnace to the entire HVAC unit the shaft. 'S not closed ( not stuck together ) ; there 's a Natural gas.... And he keeps telling me it 's interesting because you 're describing two different problems that might have. They should include faulty thermostats, bad wiring, and I have an electric furnace contacted at or! The roller by winding one turn of electrical tape around it works great heats the.! Or `` off '' setting or intermediately one or the other Honeywell L4064B fan limit switch for. And supply plenum have cooled down system test to confirm there ’ s heated or not your furnace wont off! Is not blocking air flow through the thermostat when to turn gas back on furnace does n't help refuses! Oil or gas furnace that determines when the furnace get too high &! ( not stuck together ) ; there 's clearly a gap so circuit is open L4064W Tradeline controller an...

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