I have a 12 year old Carrier central a/c unit. The compressor (R-22, 230 Volts "scroll" type) has been displaying some strange behavior for the past year or so. When my a/c guy came over last year, he thought it just needed a charge and that the system might possibly have a very small leak (couldn't find one with the electronic "sniffer", but it was quite windy that day and he couldn't take proper readings around the compressor unit's coils).
I hadn't at that time realized that it was acting strangely and that its cooling behavior seemed to depend on outside temperature. When it is very hot outside (say, >95 F) sometimes the compressor starts but doesn't cool properly. I placed an electronic thermometer in the first air duct output. Normal operation seems to happen when the air temperature in the duct is between 55-62 F (depending on outside temp). However, sometimes the compressor runs but the duct air temp stays around 68-72 F. Cycling the compressor (switching off, waiting a number of seconds, switching back on) normally seems to fix the problem. I also took "clamp" amp readings (I am in the electrical/electronic field) and each leg draws around 7-8 amps when it doesn't cool properly and around 12 to 14 amps when it does.
We just got a cold front into Texas and the temperature yesterday night fell quite a bit. It is warming up during the day but the compressor refused to cool properly even after cycling this morning a few times (did not draw more than 8.5 per leg). Leaving it on for 20 minutes and then cycling again got it back to normal cooling (and normal amp draw) which seems to show it only wants to work normally when it is hot.
Is this something you guys have seen before? Could a lack of charge (or maybe air/moisture in the system) cause this kind of symptom? Maybe the leak (if there is one) might have gotten worse? Or could this be a sign that the compressor is "shot"?
Any input greatly appreciated. I am trying to find out more about this problem before I call my a/c guy back again.