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Old 05-29-2020, 03:24 PM   #1
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Draft Inducer Cycling When Thermostat Calls For Cooling?


Weird one, just started a few weeks ago - when my thermostat calls for AC, it goes on, works fine, but the draft inducer for the furnace kicks on and off - on for like 5 seconds then off for a second or two, rinse and repeat - never stays on and never stays off. Would appreciate any help or ideas on trouble shooting before going out and buying a new controller board, unit is old, it's a ICP Furnace Model GNJ075M12A1. Have a good weekend everyone.
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Old 05-29-2020, 03:48 PM   #2
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


Welcome!

There are many previous comments on this topic.

Do an Advanced Search under HVAC section on word 'inducer'.

Sometimes drain hose gets clogged. Carefully disconnect at each end and blow thru it. If cracked at one or both ends cut off just as much as necessary to get a clean end.

Sometimes pressure switch is becoming unreliable.

Keep us advised.

That's usual answer for heating call.

Did you change or modify thermostat recently?

Last edited by diyorpay; 05-29-2020 at 03:51 PM.
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Old 05-29-2020, 04:05 PM   #3
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


Thanks but there are no other posts specific to the problem of the draft inducer being called on when the AC is asked for; it's is only supposed to be turned on when HEAT is asked for.
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Old 05-29-2020, 04:08 PM   #4
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


What kind of thermostat do you have?
Do you have a heatpump or straight a/c?

You can try disconnecting and taping off the wire(s) connected to W on the circuit board.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 05-29-2020, 04:40 PM   #5
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


AC and has heater; condenser unit out side, then the air feed to the blower / gas box, then to evaporator coil then to air handler box.

Thanks; just to make sure I understand what you are saying / meaning; if I was to disconnect the white wire from the controller board on the AC / GAS unit, your saying if the draft inducer still kicks on, then we are probably looking at a controller board issue? And if it doesn't turn on, then something probably tying to the thermostat?
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Old 05-29-2020, 04:55 PM   #6
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


yes - disconnect and tape off the heating wire (connected to w), restore power, turn on the a/c, see if the problem persists.

possible your stat is leaking too much current into the heating control circuit - it may be failing. this can be an issue with early electronic stats that don't use electro-mechanical relays as well as power-stealers.
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Old 05-29-2020, 05:09 PM   #7
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


Well *&^% me - white wire removed from controller board and no draft inducer fan running when AC is called. I have a Emerson Sensi thermostat - so I'm guessing this thing is bad / fried for some reason.....or the wiring. So, before I buy another thermostat, is it worth it for me to take a seperate wire and go from white on the controller board to white on the termostat just to make sure it's just not the wire?
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Old 05-29-2020, 05:14 PM   #8
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


I believe that t-stat can be set up as power stealing or use a common.

It's drawing a tiny amount of power from the heating control circuit to power itself when running the cooling.

Some furnace circuit boards don't take well to that.

Connecting the C terminal on the stat to the C terminal on the control board should solve the problem.

If you can't do that (not enough t-stat wires in the bundle and pulling a new t-stat cable isn't practical), you can put in an isolating relay.
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Old 05-29-2020, 05:23 PM   #9
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


Wow, that one went over my head. Let me see if I have this strait so I don't fry anything. My controller board has a CGYWR posts on it. There is a wire on C and Y that run to the condenser outside. I then have YWR running from from the t-stat to the controller board. I do have a C post on the t-stat that is open - are you saying to simply run a wire from C t-stat to C controller board and keep everything else like it originally was? Thanks again for all your help, really appreciate it.
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Old 05-29-2020, 06:00 PM   #10
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


Yes - C to C. Leave the existing wire connected to C alone.

It should solve the problem.

Is this the first cooling season with the existing stat?

I recommend hooking up G too so you can run the fan in continuous mode when desired.
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Old 05-29-2020, 06:10 PM   #11
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Re: Draft Inducer Cycling When Thermostat Calls For Cooling?


You sir are a genius - everything works, thanks again and cheers with a virtual beer.

I've had the same setup with same stat for over 5 years with no changes, for whatever reason it worked fine in the past but not this year. All the best.
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