My Carrier AC won't start when I turn it on using the thermostat (4-wire programmable). The furnace fan comes on but the ac fan/compressor is dead. I checked the breakers- they are all on. I checked the service disconnect- nothing seems wrong. I looked for loose wires in the fan/compressor unit- nothing seems wrong. Then I opened up the furnace and found a suspect conduit coming from the AC unit... this conduit has a two wires; a white wire connected to 'C' on the Honeywell control board, and red wire that is not connected anywhere! This seems like it may be the cause of the problem, but I'm not sure where this red wire should be connected, if even if it should be? Please help! :confused:

Usually the red wire is attached to the Y or yellow wire from the thermostat. It is thermostat cooling leg that tells the outside unit to turn on. Before you connect it I would check to see why someone disconnected it to start with. The unit could be experiencing a problem or the entire story of this unit has not been posted. Wires do not disconnect themselves usually.

Thanks HVAC 1000! In the fall I had the furnace cleaned and I suspect that they accidentally knocked the wire loose. Nobody else has been in there since, and the AC worked fine before that. What you say also makes sense according to the wiring diagram, but I'm completely green when reading those so I didn't want to take any chances. As far as I know, that's the whole story. I think I'll reconnect- thanks again.

Well, I connected it but it still won't turn on. What are the chances of 2 things going wrong at once?

What are the chances of 2 things going wrong at once

Not the usual case but anything is possible. Are you sure you connected the wire to the correct location?

I connected to the 'Y' terminal on the control board. Am I missing something?

The Y terminal should have done it. Looks like you are going to have to track down the low voltage circuit and see where the problem is. I would check to see if you have 24 volts across the C and Y terminals where the thermostat control circuit goes outside and work your way back from there.

Are/were there 2 wires connected to the "Y" terminal on the control board? There should be...

Yes, there are two wires connected to the Y terminal... one from the thermostat, one from the outside.

If the outdoor unit is equipped with a low pressure switch AND you have experienced a loss of refrigerant, it may explain why the unit won't run. Try this: disconnect wires from "R" and "Y" at the thermostat and connect them together. Does the outdoor unit run? If so, the thermostat is the culprit. If not, the above suggestion gains some strength...

Well, thanks everybody. I'm not sure why, but I tried the system again and it works. It seems that connecting the wire to the Y terminal was all it needed.

Glad you got it going.

I just had the same problem. I replaced the motor with no luck. It turned out to be a bad capacitor. If it is a dual capacitor, three prongs on top, it also starts the compressor. It is recommended to replace the capacitor anytime you replace a motor. I would try replacing the capacitor first. It is a lot cheaper that a new motor. If that does not fix the problem then you can get a motor. No harm, no foul. The slow start of the motor is a common symptom of a bad capacitor. The motor is not getting enough voltage. The capacitor increases the voltage like a transformer. It will boost it to almost 400 volts, depending on your unit.