I've been looking at a lot of dual fuel heat pumps and I'll have to say that the configurations are a puzzle to a lot of us. First of all, you're dealing with a heat pump. That means that the same unit is used for heating and cooling. You have a reversing valve that makes it like turning a window ac unit around and blowing the hot exhaust into the house to heat it. A clever idea and very efficient.

A:: Not only groaning sounds, but the outdoor unit fan stops and the ice thaws. This is a normal occurence because the condensed moisture on the outside unit needs thawing for the heat pump to work.Steam happens.

A:Your wiring may be wrong Your auxiliary heat should be compensating for the unit going into cooling mode(reversing)by heating the inside air.

A; At a certain point, Heat pumps become less efficient and also the icing and defrosting  is not appealing to some.

 

Here are two ways of setting up dual fuel heat pumps

1. In the restricted mode of operation an outdoor

temperature sensor is used to cause the unit to operate in the

heat pump mode above a selected outdoor temperature and to

operate in the gas heating mode below the selected outdoor

temperature. The gas heat will operate with the heat pump when

the unit requires a defrost cycle. The gas heat is used to offset

the effect of the unit going into the cooling mode during defrost.

 The unit will be commanded to transition to

gas heat even when the outdoor temperature is above the

selected outdoor temperature changeover point if the heat

pump capacity is not enough to maintain the indoor temperature

at the desired heating setpoint.

2. A non-restricted mode of operation allows the unit to

operate in the heat pump mode during the first or second call, or

stage, of heat commanded by the indoor thermostat. During the

first stage of heat pump mode the heat pump will operate on low

speed. During the second stage, the heat pump will operate on

high speed. If the heat pump capacity is sufficient, gas heat will

not be required. If the heat pump capacity is not enough to

maintain the indoor temperature at the desired heating setpoint,

the thermostat will call for the third stage of heat. At that point,

the gas heat will begin to operate and the heat pump will be

locked out. As in the restricted mode, the gas heat will act as

supplementary heat during the unit’s defrost cycle.

If the outdoor sensor is set high enough, the heat pump would not need the defrost cycle but efficieny would be lost.