Heat Pumps---The compressor operates the EXACT SAME as in COLD mode. ALL a Heat Pump does is REVERSE the flow of coolant to remove cold that results in heat by a REVERSING valve. What is the outside(ambient) temp where you are located? HP's do not function well in temps over 65 degrees. It will cause the compressor to work harder and pull more amps. What type of noise is it making? IF on TRUE 50 amp service(which is actually 100 amps), you should have no issues or voltage problems. IF you are on CHEATED 50 amp service, then you will have voltage problems. True 50 amp is a total of 50 amps on each leg. Cheated is 25/30 amps on each leg. AND if Cheated 50 amp service you should not be paying for 50 amp service as they are not giving you true 50 amp. Doug