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Yesterday evening I noticed it was getting a little warm so I checked my thermostat. I tried to turn on the blower only and it would not come on, neither would the compressor and fan outside when I tried them. I checked inside my furnace and smelled a burnt plastic smell which I traced to the transformer in the control box. To be safe I went this morning and got a new transformer, 120v primary and 24v secondary like before (except this one had 240 and one other on it as well) and a new relay. Once I installed these pieces the blower will turn on but the compressor and fan still will not when I tell it to. When I do try to turn the compressor on with the thermostat the new relay buzzes like crazy.

I can go outside and push in the contactor manually and the fan and compressor will both come on. Even if I have the thermostat set for them come on, and I go outside and press the contactor, they will come on until I let go, then the contactor wont stay in place like it should and they just turn off again.

I am beginning to think that maybe the contactor is bad as well, clearly I fixed something if the blower will come on now, it's an improvement over no air movement. Any suggestions?

EDIT: Forgot, the control box in the furnace is a A/C Blower relay control module 901955. The relay that was in it is a Products Unlimited 6205370, the new one I bought is White Rodgers 90-380 or 184-919. It has the same specs on the label.

Hi,

Look on the sides of the contactor for the small wire connected to each side, those are to the contactor coil.


Use a volt-ohm meter to test for voltage there. First test across them, then test each one separately to a good ground for 24VAC.



Thanks,
Robert

Thanks, I'll go check it out.

Checked it, no voltage is getting to the contactor, the wires leading to it though do have continuity.

Well, I applied 24v directly to the contractor from the transformer, bypassing the relay, and it worked as it should. So would that mean the new relay I just put in is already broken or perhaps the wiring is mixed. I followed the diagram and put everything back where it should be, at least I'm pretty sure of it.

Woo! Typing out these problems made me think about it. After the wire having continuity but passing no voltage issue I grabbed some old speaker wire I had laying around, used it instead of the wire leading to the contactor from the relay/transformer, and the system started right up like nothing was wrong. All that work for a little damaged wire... I guess thats how it goes sometimes, eh? Thanks for the suggestion, that set me on the right path.

You're very welcome, happy to help. The fan relay is for the indoor blower motor only, it is not part of the outdoor circuit.



Thanks,
Robert