There is a reversing valve that is energized by the O/B Stat. There are different set ups for heat pumps but they usually have TXV or Piston, if there is two metering devices (outdoor and indoor) they will have a check valve diversion path depending on flow. If there is only one metering device like on ductless splits then both lines need to be insulated. There are many different types of metering devices used, the best way to learn is to read the manufactures specs on each unit you install so you fully understand how it operates. Ultimately when you are talking about heat pumps you don't use the term evaporator or condenser, you use indoor unit and outdoor unit. The reversing valve is located in the outdoor unit, the discharge line enters the reversing valve, there are three outlets, in heating mode the hi pressure hi temp super heated Vapour travels to the indoor unit to heat the house, the indoor coil rejects the heat to the house and condenses the refrigerant and it flows back to the outdoor unit where it picks up heat from outside to turn into a low temp, low pressure, super heated vapour. Vice versa.. If you draw it out on a sheet of paper it makes more sense. If your airflow in your indoor unit is to low you will have a high head pressure and your compressor will die prematurely, this is one of the major malfunction because techs don't take the time to set up the unit in heating mode..

 

Typically two metering devices, one at each coil on either end of the liquid line.

They will meter in one direction, and open/bypass in the other.

 

Ok..one of the tech where I work told me he ran into a unit where only the indoor coil and heat pump were replaced not the air handler. He told me that the indoor coil was for a straight ac and equipped with txv and that it was causing the compressor to thermal overload cause the txv wasn't bi flow, any truth to that?..so I started to think that it wouldn't matter as long as the outside unit has check valves for proper direction of refrigerant flow that it wouldn't matter if it was a straight ac coil..

 

Indoor txv needs to be a check-txv for heat pump operation, one that will bypass in heating. "Bi-flow" was probably not the best word choice.

 

I appreciate schooling me to the proper term.. So a straight AC coil will definitely not operate with a heat pump..and the indoor coil has to be matching to the heat pump with a check-txv,rite?

 

The coil does not really care (it just needs to be sized properly). The metering device needs to be able to open up and bypass in heating.

Read RACMT's post again, then google a diagram of a heat pump refrigeration cycle to get a visual of what's going on.

It's the same as any other refer circuit, except the reversing valve will reverse the flow of refrigerant.

When it goes the other way (heating) the expansion valve at the indoor coil will bypass, and the one at the outdoor unit will meter (swappping their roles - indoor is now condenser, and outdoor is now evaporator).

 

Cool and thanks