Hi,

can someone explain exactly what happens during a heat pump defrost cycle and in a heat pump start up/shut down cycle when used in heating mode.

Obviously the reversing valve operates and hot refrigerant is cycled in reverse to defrost the heat exchanger but is the compressor stopped first and a time allowed for the pressures to equalise or does it just reverse?

Also, it seems the reversing valve (in the unit I have) is set in the cooling mode when de-energised. When energised it changes to the heating mode. Should there be a delay in the valve changing and the compressor starting (in startup) and a delay between the compressor stopping and the valve de-energising in shut down?

Thanks,

Nigel