Central AC Help Please

[scmhogg]

I have a forced air AC system. Just today, the outdoor compressor unit does not shut down when the thermostat goes off. The fan stops as usual, but the compressor does not.

I first noticed it this morning when I saw the ice build up on the coolant connections. I tried shutting the system down for a while, hoping it would reset itself, to no avail.

Help!

Steve

[Tom Miller]

The fan stops as usual, but the compressor does not.

Do you mean the blower fan that circulates air inside the house, or the cooling fan on the outside compressor unit? I'm assuming the former, because the latter would be a lot harder to explain.

Sounds like a bad relay unit to the compressor??? Not sure where this might be on your system, or if it's a "real" relay, as opposed to an IC on a board. If the latter, you'll probably have to swap the controller board. This is mostly a WAG on my part, though. Someone more knowledgeable should be along shortly...

Regards,
Tom

[scmhogg]

Tom,

The compressor and the cooling fan on the outside unit continues to run when the thermostat shuts the blower fan down.

Steve

[vaking]

I would start with the simplest test possible - disconnect the wire in the thermostat. If your thermostat controls only cooling - there will be 2 wires only. Disconnect either of the 2. If the thermostat controls heating and cooling - there will be 4 wires. You will have to figure out the 2 for cooling and disconnect one of them. With the wire disconnected the thermostat itself is out of the picture. The compressor is expected to stop. If it does - thermostat itself is in question, not the compressor. If it does not - the problem is outside your house.