I have installed a three zone Trane XL16i heat pump with variable speed air handler. One of the zones has a programmable thermostat, the other two zones have non-programmable thermostats(TCONT800 and TCONT402).
The heat pump is sometimes very noisy when it is powered on, but settles in after a bit and runs quietly -- most of the time. Occasionally it does not quieten down and the contractor indicates it is running backwards. I can shut if off for an hour or so and it will restart normally. I think I have seen this referred to as "slugging". What are possible reasons for this happening?
The contractor replaced the first compressor, and it ran fine all summer. But when I switched back to heat late this fall, the problem resurfaced.