AC wasn't cooling (compressor wasn't running) on system and after a lot of troubleshooting - I installed a whole new outside condenser unit (this is at an apartment complex). The unit worked great - for one day! Then the compressor quit running. Fan is still running. I have checked everything I can think of but what would cause this with two different units? Please help I need to get this fixed now if I want to keep my job!

Non-condenseables, TXV.

Did compressor go out on a thermal?

Air flow over evaporator.

Did you do superheat/subcooling calcs?

After unit was installed valves were released and cooling was good for 2 days now the high side 4 reads around 240 but the a coil does not get cold

What does [quote=papa_D]valves were released[/quote' mean?

Vaccumed? How far? How long dos it hold? Check for leaks?
Pressures don't mean much.

Kiss brings up some great points. Was the system vaccumed, and tested for leaks. Was the correct unit installed(r22, or r410, and matching tonage for evap coil). There are just so many things that could have gone wrong with improper install and setup. Are you licensed to work with refrigerents and systems. Pressures will actually tell a story, but you need to know what your looking for. There may be blockage in filter/drier, or oriface at a/coil(if present), or faulty tev/txv, like I said, just too many options. Please let us know more on this. Good luck.

I am certified . It's an r 22 system. Was vacuumed properly . It is the second unit installed within a couple months .I didn't install the first one but the compressor went to ground. It only lasted a month. There isn't a line dryer on the system. Is it possible for piston be blocked at a coil ?

Its possible that the problem is electrical as on contactot or loose connections. Could also be mgr lot specific defect.

Yes, its very possible. Usually, you will see normal, or a little high on the liquid side, and low or even pulling a vac on the suction side, if you see this, it indicates a plugged piston. This is where the suction side pressure will give a good clue as to what is happening in the system. If indeed you find this to be your problem, I would add a filter drier while the system is opened for cleaning of the piston.

Was there a lot of oil in the lines when you took the old unit out? This will tell you if you have a blocked line dryer. If the piston in the coil was blocked you would have a high head pressure and low suction pressure. Did you check to see if the compressor is out on overload?