I'm working on a heat pump that is water cooled, and the problem I am having is the person before I worked on it put in a new compressor that is having pressure problems. My boss says I should charge the unit up in the heat mode since it is winter, and check for at least 50psi on the low side, and about 225 psi on the high side.

When I looked at the unit the condenser had frost on it, and the compressor was hot. It has a klixon external overload switch which kicks off the unit in case of it overheating, etc.
When I charge up the unit, the low side goes down to 5 or 10 psi, but when I turn the unit off, it equalizes with the high side at 110 to 125 psi. When I turn it on, the high side reading is about 140 psi, and the low side reading shoots down to 10 psi.

It takes a charge, but it seems like it takes forever and the low side never gets me to where I want it to which is 50-55 psi in heat mode. The water temps on the inlet and outlet are 72* and 71* degrees respectively, but the compressor is hot to the touch.

What could be the problem? Should I let the compressor cool off totally, and put the freon in hot water then try to charge the unit allowing it to flow through faster before the compressor gets hot again, or could there be another problem?

I hope there may be a tech that can help me, and if I can also call you on the phone to walk me through this thing, because it is giving me hell.

Thanks.

Check for a restriction in the metering device I.e. Expansion valve/flow rater/piston or whatever the unit uses. The suction pressures are to low indicating a restriction of the refrigerant going into the coil. This will also cause overheating of compressor since the compressor is cooled by the returning gas.

Pump down and take the expansion device loose and look for dirt and debris or other restrictions like waxing. The problem with waxing is that unless you get it apart right away the wax will melt away.

Since a compressor was just changed you might also check the suction side of the compressor. There is a fine mesh screen there to catch debris also. If some idiot used soft solder instead of 15% or other braze stick they might have loaded it up with BB's of solder and that will really cause a bad restriction and low suction pressures. If the braze job was really bad stick braze alloy can cause the same thing. Usually if you look at a braze joint you can tell good from bad.

Most systems will balance out when shut down weather they are restricted or not. The only time they will not balance out on shut down is if the restriction is permanent and not floating or if something like the cap lines are fully plugged.

Was a new filter dryer installed during the compressor change? Was a suction line filter dryer installed during the compressor change? If a suction dryer was installed you can also tap the shrader valves on it to help in diagnostics. If a new filter was not installed now is the time to do it and if the old filter was left in remove it and replace with new. if you know why the old compressor was replaced it would be a good idea to post that also since a mechanical failure or a burn out can change the complexion of things.

A complete model number would be nice so if I can find info I can post it for you. I may not have the info but with a model # I can look. I do not do phone walk through's since I get my fill of that from local hvac companys on a almost daily basis but if I have time I can communicate using this venue. There are also some other good tech's on this board that might have some ideas for you.