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dsjoiner 01-01-2009 12:40 PM

Outside condensating unit continues to run
Lately I've noticed that the outside unit continues to run with no heat coming from the vents. When the thermostat clicks, the heat starts and will continue to run until, of course, the set temp is reached, but the outside unit continues to run, even after the temp is reached.

After some searching, I was sure it was the contact block that's supposed to be located in/at the outside unit. But I ran across the suggestion to turn the thermostat to "off" and if the fan stopped, it was more than likely something to do with the control wiring.

After a flick of the switch, viola! the outside fan stops. turn the therm back on and the fan doesn't start again until the next cycle, then the fan continues to run.

I would appreciate any/all help as to where to start looking at this control wire. Could it be the thermostat has gone bad? How to check? Could it be some creature has invaded the crawl space and chewed through some wiring? Could it still be the contact switch at the outside unit? My reading has indicated this should be less than a $20 DIY project if so.

As you can tell, I'm stuck and in our area, decent HVAC people are few and far between, then coupled with a holiday, even more so. Any help will most definitely be appreciated!

If it helps, the unit under the house is a carrier and the outside part is a Bryant...........

glennjanie 01-02-2009 12:38 PM

Welcome DSJoiner:
When the outside unit continues to run, does it show any frost or icing? It may be a defrost cycle causing the unit to continue to run. After it runs for a while, there should be a high perssure limit switch to shut the compressor off.
Is it the compressor running or just the fan on the outdoor unit? If the compressor continues to run more than 10 minutes after the heat cycle, it would probably be the high presssure limit switch.
Otherwise, a relay may not be doing its job, whether in the outside unit or the inside unit but the relays should be in the inside unit.

dsjoiner 01-02-2009 01:40 PM

The outside unit shows no frost or icing. Best I can tell, it's only the fan. But is there an easy way to determine if the compressor is running also? Where can one find this high pressure limit switch and is there a way to either check or test? Or, is this a job that's better left to the pros? Thanks for the kindness of a response....

glennjanie 01-03-2009 03:19 PM

Hello DSJoiner:
The compressor is inside the condenser unit (outside). You can hear it by putting your ear against the unit, it sounds like a small engine running and has some vibration to it.

The high pressure switch should be inside the condenser unit and will be attached to the refrigerant line with one or more wires coming out the back of it. You can find it by looking at the schematic drawing on the back of the access panel. Testing requires a set of refrigeration gauges.

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