AC Unit keeps running in Heat & Cool


Old 04-02-03, 08:06 PM
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AC Unit keeps running in Heat & Cool

I have a Carrier 4.5 ton AC unit that has recenlty continued to cycle wether I have the thermostat in Heat or Cool. Even after the blower shuts down the outside unit continues to run and cycle. In heat it runs - goes into defrost mode- and then runs again. In cool it continues to run until the lagre line starts to freeze. What should I look to replace? Control board, a relay, coil?

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Old 04-02-03, 08:42 PM
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You should really call a pro.

If you know what the contactor in the outdoor unit looks like check it with the power off and see if it's stuck. If so replace it.
Old 04-02-03, 09:55 PM
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Cool Elimination....

Try to eliminate the control in this case the thermostat...Did you by chance replace this recently?? You'll need 3 jumpers.. Kill the power first...Label and then remove the thermostat wires at the air handler terminal board. First place a jumper from R to Y and R to G... Apply power...the unit should run in the heat place the 3rd jumper from the O terminal to R and the reversing valve should pop over to run in cooling. Be carefull not to touch the jumper to ground or you could blow the transformer. This is all low voltage (24V) remove the connections from R and everything should stop..Start there..If all this works OK , you'll probably be replacing the T'stat...or the stat wire......
Old 04-03-03, 12:38 PM
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A/C runs

You said . In cool it runs till the large line starts to frost. This sounds like your are also low on freon and the unit shuts off on the low pressure switch. You should get a tech to look at it and see if it is the wire, tstat, or relay. ED
Old 04-03-03, 05:28 PM
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It's Fixed !!!

Thanks all for the help folks. I was able to isolate it to the contactor.

The points on 1 leg were pitted closed. We are running fine.

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