Heatpump failure

[Avro]

Looking for a professional opinion. Okay, I had a tech install a new gas furnace but installed the humidifier to the O terminal. So when the humidifier came on the reversing valve fliped to AC when in heating mode. Shortly after fixing the wires, the pump burned out. Question is, would the sudden change of pressure from running the heat pump in heat mode flipping to AC mode cause damage to the pump?

[Porcupinepuffer]

I don't believe that would negatively affect the actual compressor. You would end up with low pressures by running the a/c in winter that may cause the coil to freeze up, but I don't believe there would be any issue that would stress the compressor to make it fail. How old is this heat pump?

[Avro]

Its about 8 years old.  Not an expert but this sequence in operation would be the same as when the heat pump goes into defrost mode, correct?  Or is there a delay when the reversing valve operates into defrost mode to protect the compressor?

[Porcupinepuffer]

It's similar to defrost mode excecpt in defrost mode the outdoor fan will not run or cycle to keep the outdoor condensing temperature high to allow for a proper defrost to take place.
There is always a minor delay in the reversing valve since the small solenoid that changes the direction of the valve in the cooling position actually changes flow of small lines to the larger valve body that allows a sliding mechanicsm to move over to the opposite side and reverse the flow. So a reversing valve can never really change direction without the help of the compressor pumping to complete the process.

A compressor burnout on 8 years is either a fault of bad luck with a poorly made compressor, or more than likely a fault in the initial installation that may not have included a proper vacuum under 500 microns to ensure no moisture was in the system.