Issues with furnace and compressor

[NoOne0785]

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.

[Robert]

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

[NoOne0785]

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.

[NoOne0785]

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.

[NoOne0785]

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.

[Robert]

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