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Problem: Fan will not come on in the “On” position or your fan will not come on when you turn the thermostat down

 

Problem: Fan will not come on in the “ON” position or your fan will not come on when you turn the thermostat down in the air conditioning mode.

Solution: Test to make sure you are getting 24 to 28 volts AC between the G (green) and C (com) terminals on you fan center or control board. If you aren’t getting 24 volts between G and C then you might have a thermostat problem, a thermostat wire problem or the low voltage fuse on the control board might be blown. Below we have a picture of a control board that shows the low voltage fuse. If you think you need a control board please email us with your furnace’s model number and we will be glad to try a find the right board for your furnace. Our email address is: support@arnoldservice.com You might need a new fan center relay (if your furnace is equipped), fan sequencer or furnace control board.

Nordyneboard903106instructions

A sequencer looks like the picture below. Sequencers are used most of the time in air handlers (heat pumps, electric furnaces) to control the fan blower and turn on the electric heaters in a sequence so the electric heaters to do come on all at the same time. Most of the newer air handlers have electronic circuit boards. You should have continuity between M1 and M2 when 24 volts Ac is applied to the bottom terminals. We have sequencers for sale on our site. Please search for “sequencers”.

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2 Stack Sequencer

Purpose of the Fan Center Relay: The purpose of the fan center relay is to provide a low voltage control (24 Volts) to control a relay that can be used to control two-speed blower motors and auxiliary circuits in heating or cooling equipment. Many of the newer furnaces do not have fan center relays, but many of the older furnaces and some new furnaces still do. You would need to look inside your furnace to determine if you have a fan center relay. Some of the relays are attached to a junction box where the power comes into the furnace, and others are located in the blower compartment attached to the blower housing. You might not have the relay that we sell below. Many of the newer furnaces are control by electronic circuit boards. We sell the White-Rodgers fan control center on our site. Please search for “fan center”. If you think the control board is causing the fan to not come on please send us your furnace’s model number and we will try and find out which control board your furnace uses. Our email address is: support@arnoldservice.com

Troubleshooting procedure:

1. Make sure that your furnace switch is “ON” the furnace blower compartment door is on and secure. Move the lever on the thermostat to the “ON” position. The fan blower should come on. If it doesn’t then you probably have loose or burnt wires in behind the relay or you may need a new fan relay or circuit board.
2. Many times wires are either loose or burnt behind the fan center relay. First make sure your furnace power is turned off. Remove the fan center relay and inspect it for loose or burnt wires. Repair wires and reinstall fan center relay. Turn the power to the furnace back “ON.” Hopefully you have fixed the problem!
3. With the furnace on use a multimeter set to AC Volts, to test between terminals “R” and “C.” You should get a voltage reading of approximately 24 volts AC. If you do not get any voltage reading, your low voltage transformer might need replacing or you are not getting high voltage to power the transformer. Sometimes furnace manufacturer’s connect the furnaces transformer through the limit control so if your furnace over heats or if the limit is stuck open then you will not get power to the transformer. There are quiet a few variables that can occur to cause furnace problems. I believe I have covered the main problems. If you have the fan center relay like we sell below the low voltage transformer is combined with the fan relay. This relay will work on motors up to 3/4 horse power.

22 thoughts on “Problem: Fan will not come on in the “On” position or your fan will not come on when you turn the thermostat down

  1. I have a Goodman 1 Ton AHU.. Forced Hot Air/AC..
    HEATING – Blower comes on when Tstat calls for heat.. Tstat starts HW Pump, once coil Hot enough (Strap on Aquastat) the Blower Starts like clock work – No Issues at all during HEAT call.

    Without Heat Call, blower does not start in Circulation or Manual On Mode from Honeywell Stat TH811.. What could cause this? I have to zones, switched faces of Tstat, same issue – So Tstat good..

    This past summer I was having issues with cooling.. Changed Blower and Capacitor in trying to diagnose. Intermittently the blower would not come on causing a freeze up at the condenser. Thats what started this.. Now Im seeing the heating side..

    1. Hi Chris! I really do not know that much about your setup with hot water heat and zone heating that you have. I would like to suggest that you check and see if the G (green) to C (com) wire is getting 24 to 28 volts AC when the thermostat is calling for the blower to be on in “Fan On” mode. If you are not getting 24 volts between G and C when the thermostat is calling for the blower to be on in Fan ON mode then you might have a thermostat problem or a thermostat wire problem. So sorry I do not not much about hot water heat pumps. I hope you can find a simple fix. Steve

  2. I have a less than a year old american standard heat pump it wont turn the heat or a/c on I tried to turn fan to on position still does nothing. It has a pro series honeywell thermostat I pulled it changed batteries still nothing. Left for town to get a few small heaters I got called said heat is working now it worked all night about midday same thing no power.

    1. Hi Dennis! This sounds like you might have a loose wire connection a control board, or thermostat that is going out. You would need to test with a voltmeter when the problem occurs to find where the problem is. I would like to suggest that you test down at your air handler where all the thermostat wires are joined together at the air handler. You will have to take the wire nuts off the thermostat wires to test the bare wires where they are joined together. The next time when your unit will not work set your voltmeter to “Volts AC” and test between the R and C connections you should have 24 volts. With the thermostat calling for heating you should have 24 volts between Y and C, G and C, O and C, R and C. If you do not have 24 volts between those wires then you either have a thermostat problem, thermostat wire problem (loose or broken wires) or a low voltage transformer problem. If the fan will not come on you might have a fan relay problem. I hope you can easily find and fix the problem. If you would like me to look up parts then please send me your air handler’s model number to our email address arnoldservice@gmail.com. I hope you can find the problem soon! Steve

  3. Hello,
    I have a mid 90s Nordyne furnace. According to the wiring diagram it is a 2 wire hookup, red and white. However it looks like the previous owner added AC and added in a fan relay switch along with a 4 wire tstat. The AC was removed prior to us purchasing and we are just trying to get the heat working. The furnace fires, but the blower motor won’t come on in either auto or run. I have double and triple checked the wiring diagram and everything in there is correct, with the exception of it not showing the fan relay. Right now the tstat green is hooked up to one side of the 24v relay, and the red (rh) is hooked up to the other side. Ive tried changing to the White and green as well as white and red to the relay and it won’t come on. We can manually switch the relay and it works, but then the was will always run regardless of heating or not. Bad relay? Bad control board? Something else? Should it be green to one side of the relay and power off the 24v transformer to the other side?

    1. Hi Nathan! The control board should time the length of time between when the burners ignite and the blower fan comes on. The control board should control the blower in the heating mode as long as one of the blower speeds are hooked up to one of the blower speeds terminals on the control board. There should be a “heat” terminal on your control board on most control boards. The fan should run in AC mode and with the “Fan ON” through the green “G” connection. So if you tie the Red (low voltage power wire) to the G (green wire most of the time green in color) together the fan should start and operate until the red and green are disconnected. If you are getting 24 volts AC between the G and C (common) wires on your control board and the fan is not running then you either have a bad control board, the blower motor is not hooked up, blower motor capacitor is weak or bad or blower motor winding is bad. I would suggest checking to see if the blower motor is getting 120 volts to the blower motor when the thermostat is set to “Fan ON”. If you aren’t getting 120 volts to the blower motor then more than likely you need a new control board. I hope you can easily find and fix the problem. Steve

  4. Just replaced my Bryant 90 plus with a new circuit board and thermostat. Everything seems to run fine however when i place the fan switch to the on position it will not work. You can hear the relay firing on the control board but nothing. If i switch the AC on then the blower motor works just fine. We tried jumping the red and green at the board to see if that would work and still just. Click from the relay. We are at a loss here and don’t know what else it could be. Any help would be appreciated.

    1. Hi Jayson! Yes, that is weird about what is happening! The thing that is throwing me off is the fact that the blower will run just fine when you have the air conditioning running. The control board is energized through the green thermostat wire the same way in both the “Fan ON” mode and the air conditioning ON mode. I would like to suggest that if you have not already to make sure all wires are good and tight especially the ground, common wire off your low voltage transformer. What really threw me for a loop was when you said that you directly connected the red wire to the G connection on the control board and the fan still would not run. The blower motor most certainly should have run with a direct connection between R and G. I would suggest that you check your low voltage between G and Com (C) when the thermostat is both in AC mode with the AC running and in the “Fan ON” mode when the blower will not turn on. You should have a minimum of 24 volts AC between the G and C wires at all times. If the voltage is below 24 volts then you might have a weak low voltage transformer, thermostat problem or a bad, loose thermostat wire problem. I would also suggest that you make sure the capacitor is good on your furnace’s blower motor and that you are getting a minimum of 110 volts to the blower motor when the thermostat is calling for the blower to be ON. Sorry that I can not be of more help. This is pretty unusual. I hope you can quickly find and fix the problem. Steve

  5. I recently replaced the run capacitor on the air conditioner outside cause the fan and compressor wasn’t coming on. Now the inside Goodman gas/ electric furnace blower isn’t coming on at all but it’s buzzing then nothing at all.

    1. Hi Sam! Replacing the outdoor capacitor should not have anything to do with the indoor blower fan not coming on. You could either have a bad or weak indoor fan motor capacitor or a fan motor that is going out. I would try replacing the indoor fan motor capacitor first since it is a lot less expensive than a new fan motor. If a new capacitor does not fix the indoor fan motor then I would suggest that you check with a voltmeter to make sure that the motor is getting 220 to 245 volts AC. If the motor is getting the right voltage and the motor is still humming and will not start then you will need to purchase a new fan motor. If you would like for me to look it up and see which motor your air handler uses then please send me your air handler’s model number to our email: arnoldservice@gmail.com I hope it is just a capacitor problem. Steve

  6. I have a simple ICP Central AC unit in the house I bought last year. The AC is about 5 years old, and worked perfect. This year, i had trouble with the blower motor not always coming on when the unit started up. I found that if i turned of the breaker to the Air Handler, and would wait 10 minutes, then turn it back on, it works normally. I replaced the run capacitor and the contactor, and it ran perfect for a week, now back to it was. Runs all day, but after being less active at night, I have to reset power, then works again. Any ideas on what may be the cause? Thank you..

    1. Hi Jason! I assume that you are referring to the indoor blower motor that will not come on all the time. I would think that this is an air handler control board problem, but it could be a thermostat problem. I would like to suggest that you test with a voltmeter the next time the blower motor will not come on. Make sure you are getting 24 volts between the G and C (common) thermostat wires when you are having trouble with the blower coming on. If you are getting 24 volts between G and C and the blower is not coming on then you probably have a control board or fan relay problem. If you are not getting 24 volts between G and C then you probably have a thermostat or thermostat wire problem. I hope you can easily find and fix the problem. If you want me to look up parts then please send me your air handler’s manufacturer’s model number to our email address: arnoldservice@gmail.com. Steve

  7. Hello, I am looking for a control board and relay for my ICP OMD085A012 oil fired furnace
    The blower will not work in the on position but does work in cool and heat.

    Any chance that you have these parts? Thanks a million!

    Dan
    Mobile (609) 338-3111

    1. Hi Dan!
      I am sorry, but we do not sell any Oil Furnace parts. I looked up the parts you are asking about in our ICP parts program and it shows a Control Fan Timer part number 1150886. I am sorry, but I do not see a relay listed. Yes, this could be either a thermostat problem or a control board problem. I would suggest that you check with a volt meter to see if you are getting 24 volts between the G and C when you have the thermostat in the ON position. If you are not getting 24 volts with the fan in the “ON” position then I would think you have a bad thermostat. If you are getting 24 volts then you probably have a control board or fan relay problem. Hope you can easily find and fix the problem. Steve

  8. Hello Steve. I have a Trane Powerlink II heat pump system. The fan will work properly when the cool is on. Additionally, the fan will work poroperly even when the cool is not on, but only when the fan position of the thermostat is set to circulate mode. The problem is that when. I turn the fan position to “ON” the fan will not work and turn on. Essentially, if the fan is already running because the fan position is on “circulate” and the cool is off, when I turn the fan position to “ON” then the fan immediately shuts off and stops running. However, if I turn the fan position back to “circulate” or even turn the temp down to turn the cool on the fan will once again work properly. Any thoughts on how to troubleshoot where the issue lies and how to potentially fix the problem? Thank you in advance.

    1. Hi Robert! Thanks so much for the question. I am sorry, but I am not familiar with the Trane Powerlink II heat pump system or thermostat. I am guessing that maybe the installers did not hook up the G (green wire) on the thermostat. Maybe they hooked up the circulate connection on the green wire so the fan will work, but not the green wire to the G connection to turn the fan on when the thermostat is turned to fan ON. Circulate and Fan ON seemed to me to be the same thing. I am very sorry that I do not know this thermostat and thermostat wire set up. I would have to see and investigate with a voltmeter. If you want to send me some pictures of the thermostat wiring then please do to our arnoldservice@gmail.com email address. I hope you have a great day! Steve

  9. I just bought a house through the winter and we went to turn the central air on the other day and it won’t kick on. I’ve checked all the breakers and fuses, all good. I have a Honeywell T87, I have it switched to cooling mode and it will not kick on. The fan on switch will not turn the fan on either on cooling or heating. Where would my problem be? My brother in law is a HVAC guy and he told me that the wiring looked like it was done right but he didnt have a dvom with him to check for voltage anywhere. How should it be wired? I have an older armana gas furnace.

    1. Hi Chaz! I would like to suggest and see if the contactor is getting 24 volts and is being energized. You will need a volt meter to test and see where your problem is. Without a voltmeter, it would just be a guess on any one of about 10 things. If you do not have a volt meter I would like to suggest that you get one so you can test to see where the problem is located. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  10. I have an older gas furnace fan that will not come on. When the fan tries to come on, the 24 v relay buzzes, the fan turns for 1 second then stops. The fan’s relay coil does not show 24 volts except for a surge at start attempt. When I “manually” supply 24 volts to the relay coil, the blower comes on, so blower and relay are fine.

    I did recently install a web based thermostat with smart phone app and it worked fine. I like this thermostat but wonder if this is causing my problem. I have yet to ring out the voltage at the thermostat.

    The 24 volts on the bus bar near the relay is strong (that is where I manually got my 24 v from). There are no burned looking wires.

    I think the problem is between the relay and the thermostat.

    Any thoughts would help.

    1. Hi Michael! Thanks for asking the question. I would suggest that you try to measure the voltage at the control board with the fan set to “Fan ON” on the thermostat to see if you are getting 24 to 28 volts AC between the G and C (com) terminals on your control board. If you aren’t getting any voltage or voltage below 24 volts then I know that some of the new thermostats require a higher VA transformer to work right. If you have a 35 or 40 VA transformer then you might need a higher VA transformer to get your system to run correctly. This could also be a thermostat problem since you say that the voltage drops out when the fan relay tries to start. I hope you can easily find and fix the problem. Steve

  11. I have a gas heater with an electric fan. I just had my roof replaced a week ago this Saturday and it worked fine up until this point .

    Would replacing cause my fan not to come on? I know it’s probable a silly question but again it was working fine up until this point

    I appreciate your reply

    Sincerely ,
    Annie

    1. Hi Annie! Replacing the roof could only cause the fan to not come on if the roofers accidentally cut or stepped on your thermostat wires and caused a break in the wires. They could have loosened a connection up on your control board or thermostat with all the banging and vibration from hammering the roofing nails. I would suggest that you turn the power off to the furnace and make sure all wire connections are good and tight. Turn the power to the furnace back on, turn the thermostat to the “Fan ON” position and see if you are getting 24 volts between the G (Green) wire and the C (Common) wire. If you are not getting 24 volts then you either have a thermostat problem, thermostat wire problem or you might have a blown fuse on your control board. If you are getting 24 volts between C and G and the fan is not running then you might have a control board problem, fan relay problem or a bad fan motor or bad fan motor capacitor. We have a really good Youtube video on the following page that tells about the top 10 reasons why the blower fan motor will not come on. Here is the link: https://arnoldservice.com/top-10-reasons-blower-fan-motor-will-not-come-furnaces-air-conditioning-heat-pumps/ I hope you can easily find and fix the problem. Steve

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