I am a homeowner with a one year old Nordyne (NuTone) DF6SF Package unit. This is a 15 seer two stage heat pump with two stage gas emergency heat. 3 ton unit.
The unit performs excellent both in cooling and heating until the temperature gets down to around 38F. I have the thermostat set at 31F for switchover to the gas heat.
Above 38F the unit performs perfectly. Around 38F and below when there is a call for heat the unit turns on, there is a buzzing sound (compressor trying to start?) for around 5 seconds, the coil fan turns slowly about one revolution and then everything stops. About ten seconds later the unit trys to start again (same buzzing) but this time both the compressor and the coil fan start and run. Everything from this point on is normal. It never fails to start on the second try (although with the buzzing noise at start). The breaker (40amp) has never tripped.
My tech installed a factory hard start kit. This does not seem to have made an improvement. He thinks the compressor might be bad.
Both the regular start capacitor and the hard start capacitor both were tested with a capacitance meter and are fine. This check was done at an outdoor temperature of 50F.
The 40 amp breaker is new, the outside disconnect is new, and the wiring from the outside disconnect to the unit is 8 gauge and is new (a run of only 7 feet). Wiring from the breaker box to the outside disconnect is 6 gauge and is original wiring.
My questions are does this sound like a bad compressor? Is it possible that the start capacitor is bad at only low temperatures? Since the unit runs perfectly at temperatures above 40F I have my doubts about the compressor being bad.
Thanks in advance for your advice.