Understanding heat pumps

This is for Pete Campbell he asked for heat pumps so I would like to start this off with just some simple questions and answers to heat pump operation and maybe the old pros won’t find this thread tuck away in Okla:D and spoil it for those that don’t fully undrstand heat pumps be they are geo thermal or air to air type.

I will start with a easy question why do heat pumps have a dryer installed in the liquid refrigreant line with an arrow pointing both directions. This type of dryer is also a easy way to determine if a heat pump is in use as no other type of A/C unit uses this type of dryer

I don’t know…

Because the direction of flow changes between heat and AC so it is bi-directional?

Yup, bi-directional depending on which mode it is in.

Charley, do all heat pumps need this dryer? Is it neccesary for it’s operation or just an added benifet?

Its not necessary for its operation but it is necessary for longivity of the unit as the dryer traps solid contaminits and moisture that may not have been removed completely during the installation of the unit be it new or the refrigerant system was opened for repairs such as leak repairs. Moisture remaining in the system creates acid within the oil of the compressor which attacks the motor windings of the compressor

Yes a the dryer on a heat pump has to be bi-directional arrows pointing both ways

Ok next question why does the exterior fan stop operating during the defrost cycle on a heat pump.

As i see very few heat pumps here, I have some more questions. The dryer is usually installed at the exterior of the home? Also, can I run the AC side of the heat pump in the winter? Would there be an instance where the heat would work but the AC would not? I would not be able to check for AC temp, Just to check if it is operational.

The dryer is usually field installed within the first foot of the liquid (Small) refrigerant line as it exits the exterior unit. Some MFG are starting to install the dryer at the factory and it would be inside the cabinet.

A heat pump operates its self automatically in the cooling mode in the winter months every time it goes into the defrost cycle. So your answer is yes you can operate a HP in the winter in the cooling mode just don’t start it off in the cooling mode if the unit has not been operating start it in the heat mode let if operate in heat for 10 or 15 minutes then shift to cooling all this is telling you is the reversing valve does operate you are simply sending the unit manually into a defrost cycle. The indoor temps in the cooling mode tells you basically nothing. If the unit is properly charged with refrigerant and is producing heat in the heat mode the cooling cycle in the summer months would also be correct

A reversing valve takes 24 volts from the indoor thermostat to operate, the valve is a normally closed valve in the cooling mode, the coil on the valve has no power applied. In the heat mode the 24 volt coil on the valve is holding the valve open allowing the refrigerant to reverse is cycle for the heat mode. So if the reversing valve failed the unit would operate in the cooling mode but would not operate in the heat mode

Ok I will answer my own question, the fans stops to allow the defrost cycle to complete faster as the defrost terminates generally on temp of the refrigerant in the exterior condenser, it can be terminated on a timer but generally is on temp so we do not want the exterior fan operating dispersing our temp before the warm refrigerant has time to melt any ice on the coils

Name 5 visual ways to identify a heat pump

You gave us the first one-dryer with bi-directional arrow.

You can also tell by the thermostat (emergency heat setting).

A four way reversing valve.

A heat pump has a third service port usually located right above where the refrigerant lines enter the outdoor unit.

A compressor and a accumulator vs just a compressor.

Last on the outside unit there is a plate that might say heat pump on it but at a minimum it will give you the model and serial number that can be cross referenced to show that it is a heat pump.

Sometimes you can access the evaporator (inside coil) and see it on the label.

These are my guesses and I am sticking to them until you prove me wrong.

The outside unit will be installed high off the ground and sometimes have a cover to protect the blades from ice/snow up here anyway, model number usually would indicate it’s a heatpump.

It growl and steam up when it goes in defrost…

Wasn’t trying to prove ya wrong just trying to prove your right, not bad for a pup:D:p

Just for giggles lets add to the list there will be more than two low voltage 24 volt wires traveling to the exterior unit

This is the type of thread that keeps me coming back every day. So many new things to learn and so many different perspectives. Thanks Charley.

Why do heat pumps have heaters embedded in the crank case of the compressor what is its purpose and what device controls the crank case heater

On older ac units back in the r-22 era the heater was always on to prevent foaming and compressor failure during start up. I have not seen compressor heaters on newer ac’s in a while. Heat pumps are rare in the cold climate up here so I am not sure if it is the same principal at work here. No idea what controls the heater. Always on were the only type I ever saw.

Any differences that should be known about Scroll vs reciprocating compressors?

The crankcase heaters are installed at the bottom of the compressor can either be embedded in the compressor or wrapped around the bottom like a dog collar usually not very visible from just pearing into the unit from the fan area.
It is operational 24/7 as long as the unit has power applied as it is suppplied power from the Line side of the contactor its purpose is to keep the body of the compressor and the oil in the compressor warm preventing any liquid refrigerant from settling in the oil of the compressor during the off cycle. During the off cycle of the unit liquid refrigerant will always travel or migrate to the coldest area of the refrigerant loop which would be the compressor area if the crank case heater was not operational.
If liquid refrigerant settles in the compressor when the unit starts there is a high possibility that the oil from the compressor can be washed from the sump of the compressor and create damage to the compressor before the oil has a chance to return to the compressor, which would be simular to operating your vehicle with no oil in it no lubrication.

The operating control device for the crank case heater is:D the breaker in the electrical panel or the disconnect at the unit;-)

Sure is, start it off and we can talk about the differences