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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7542
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Williamsno CHB-105-DD-S2 Furnace with Central air.

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I have a Williamsno CHB-105-DD-S2 Furnace with Central air. When I turn on AC, the outisde unit begins to work. I can feel and hear the fluid flowing through the pipe to the condensor in the ductwork and the pipes near the furnace become cold. The only thing that doesn't happen is the blower motor doesn't turn on. When I turn the heat up the burner fires and the blower turns on.


I have verified that the transformer voltage is 24v AC.

Welcome to Just Answer!.

So far it sounds like the fan relay has gone bad. The test for that is set the thermostat 'fan switch' to the ON position, if the fan doesn't run. We can do a few tests.

I need to know which colors of wires go from the *thermostat to the furnace... usually there is a small red, green, white, and yellow.

Tell me what you find, we can go from there.

I hold questions open after positive ratings to allow for unlimited follow up. Please be patient though. The research & typing take time.

Customer: replied 3 years ago.

Hi Phil


You are correct. it is the fan relay. I Shut off power then removed it and attached only coil leads. I measured an open from NC to C but also had an open from NO to C. I then created a jumper and the fan motor turned on and my house is rapidly cooling.


Thanks for your help.



Fantastic! Good work on your end.

You need to disable the other side of the NC-C double pole single throw relay now however, so that if the furnace comes into heating mode it will not try to low speed fan and high speed fan at the same time and burn out the motor. Do that by removing the wire either NC or NO that you are not jumper-ing to. it goes to the speed on the motor that you are not using.


If the relay is a black plastic box about an inch and a half on a side, then it is standard, you can go to Grainger industrial supply and pick up a generic replacement.


I will put the ratings box up, if you choose to rate my advice positively I will keep the question open for unlimited follow up on the same dime so to speak.



Phil and 2 other HVAC Specialists are ready to help you
Customer: replied 3 years ago.

Thanks for the tip on Grainger. I was thinking I would have to search online and order it.

You are welcome.

Let me know if you have any trouble rating my anwser... it is how the company pays me a part of your deposit.!


After a positive rating I hold the question open for an unlimited time into the future so you can follow up later if you need to.


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