Heat Pumps and Electric Heating - Outdoor unit 'short cycling'
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geo4
02-04-07, 07:28 PM
I'm having a little trouble with my Carrier heat pump. It's 10 years old, and the indoor unit was replaced 2 1/2 years ago - the outdoor unit was given a clean bill of health at that time.
This morning, when in the back room closest to the outdoor unit, when the heater began to cycle, the indoor fans continued to run, but we could hear a loud "thunk" as the outdoor unit abruptly shut off. About 10-20 seconds later, the unit would turn back on for another minute or two, then would shut down again. The AUX light was also seen a few times.
The air in the house was/is blowing warm. I checked the air filter, which was not too dirty and I cleaned it, but no change.
For fun, I turned on the AC to its coldest setting for about 15 minutes. The outdoor unit was not icy and did not appear abnormal, but I figured the AC would warm it up a little. It seemed to do the trick for a few hours, but later in the day (as darkness set in...) the symptom returned.
I pulled off the cover to confirm that the main relay was, indeed, cutting out. AC supply was right at 230VAC. The white line in conection was a little loose at the relay - 1/8 turn on the screw snugged it up. The only other thing that I saw was that the Starting Thermistor (big blue barrel with spade terminals on the top and bottom) had rusted connectors. I removed it and scraped them clean. I also removed the circuit board to check for cracked solder joints - all looked very good. Everything else looked clean and in good order
So now I'm stumped. I am not an AC tech, but I am a long-time electronics troubleshooter. All of my online research didn't give me much info. The schematic diagrams on the cover of the unit weren't very helpful, except to identify the parts.
I'm thinking there may be a problem with the board, the thermostat, or a sensor in the system. Ideas? Any input will be helpful.
I can get the model if needed - I can't find my owner's manual, but the numbers are on the plate on the back cover.
This morning, when in the back room closest to the outdoor unit, when the heater began to cycle, the indoor fans continued to run, but we could hear a loud "thunk" as the outdoor unit abruptly shut off. About 10-20 seconds later, the unit would turn back on for another minute or two, then would shut down again. The AUX light was also seen a few times.
The air in the house was/is blowing warm. I checked the air filter, which was not too dirty and I cleaned it, but no change.
For fun, I turned on the AC to its coldest setting for about 15 minutes. The outdoor unit was not icy and did not appear abnormal, but I figured the AC would warm it up a little. It seemed to do the trick for a few hours, but later in the day (as darkness set in...) the symptom returned.
I pulled off the cover to confirm that the main relay was, indeed, cutting out. AC supply was right at 230VAC. The white line in conection was a little loose at the relay - 1/8 turn on the screw snugged it up. The only other thing that I saw was that the Starting Thermistor (big blue barrel with spade terminals on the top and bottom) had rusted connectors. I removed it and scraped them clean. I also removed the circuit board to check for cracked solder joints - all looked very good. Everything else looked clean and in good order
So now I'm stumped. I am not an AC tech, but I am a long-time electronics troubleshooter. All of my online research didn't give me much info. The schematic diagrams on the cover of the unit weren't very helpful, except to identify the parts.
I'm thinking there may be a problem with the board, the thermostat, or a sensor in the system. Ideas? Any input will be helpful.
I can get the model if needed - I can't find my owner's manual, but the numbers are on the plate on the back cover.