I have a Carrier AC-Furnace combination. My wife noticed that our outside air conditioning compressor wasn't operating yesterday. I checked and operated all of the circuit breakers, both inside and outside (by the compressor).

However, I noticed that the furnace fan, which blows the air, remained on when the thermostat was switched to Auto and Off. Normally, this should stop the fan from running.

Removing the thermostat cover, a Honeywell Model T834C1947 24 volt mercury (with a Carrier brand) which was replaced this past Fall, I noticed that the small dial inside, which is has a gauge of .2 to .9 and has "Longer" on the inside of the numbers, was burned on the .7 to .9 of the scale. The inside of the case had scorch marks as well.

Thus it looks like my thermostat may have a problem. Is there any way to check the operation of the AC compressor by bypassing the thermostat? Any other suggestions before I try calling the repairman?

Bill B

If you jumper the red and yellow wires, the compressor should start. If it does, the problem is in the thermostat or wires. For more details, check the sticky at the top of the Heating forum. It is crammed with good info.

If you jumper the red and yellow wires, the compressor should start. If it does, the problem is in the thermostat or wires. For more details, check the sticky at the top of the Heating forum. It is crammed with good info.

Labman, Thanks for the tip. I tried this, and read the sticky. With a jumper wire connecting the red and yellow wires, the compressor did not start.

So it sounds like it is something at the AC or furnace level.

Before receiving your reply, I went out and purchased a new thermostat. Again, the old one had a charred place on it. I just installed it today, though even with a bubble level, I didn't get it quite level. We'll see if the better half notices... :D

But with the new Honeywell RTH 230B thermostat, the furnace fan blower continues to run and the compressor will not start.

So I've given a local repair guy, who happened to have a link on this site, a call. We'll see if he can fix me up.

Please let me know if there is anything else I should try, or even where else to look. I've found it best to know what the repair person should be looking for ahead of them checking it out because more often than not I have to tell them where to look! :rolleyes:

Thank you again for your great help.

Bill B.

If you have to tell the repair man where to look, my advice would be to find a better service man.