Air Conditioning - AC compressor problem?

Hello,
I have a problem with my AC. Recently my upstairs AC stopped cooling. The pressures are 80psi LP and 240psi HP. Originally the compressor red 90/250 but after coil cleaning the pressure dropped to 80/240. The problem is that the unit still does not cool. Two things that would cause the problem are air in the system, or bad compressor valves - that is what the tech told me. Well, I don't believe that there is an air in the system, because the last time the unit was worked on was in 1997. So bad valves is what's left. My question is, what should new compressor cost and installation be, and if indeed valves are the problem.
The compressor numbers are
AW300ET-050-A4
AW5516H
The outdoor units model number is 10ACB18-3P made by Lennox.
Any other ideas?
Thanks,
Sfinx

Replacing the compressor would be a waste of money. Try cleaning the condensor coils really good. 80 lsp would not be considered bad if the inside of the house is already hot. What is the temprature difference of supply and return?

That is the problem, suply and return difference is about 5-8ºF. If I look on the LP and HP pipes on my outside unit thay are at the same temp, roughly 75ºF. The coil has been cleaned by me, and then in addition by the tech. It looks brand new.

Sfinx

i doubt the valves are bad, if they were, the pressures would be much closer together

i too doubt air is in the system

does it have a txv metering device?

check all return ducts, you may be pulling in hot attic air

80/240.....you should be cooling better than that at those pressures

Thanks for replys. A quick question, what is the "txv metering device"?

I will check return ducts, I agree, the attic air is very hot and you are right it could cause a problem.

Sfinx

Everyone's talking about the condenser side, what about the evap side? You mentioned that the the pipe temperatures (suction and liquid) to the condensing units were about the same temperature. That for sure isn't right. The small liquid line should be some above ambient temperature and the larger suction line should be cold and sweating. The fact that your suction pressures are about normal would indicate that sufficient refrigerant should be vaporizing and you should be getting better cooling. This brings us to conclude some possibilities:

1) The return air going past the A-coils is hotter than normal and isn't coming from the room being cooled. This would indicate a duct valve problem. You could also have a serious leak of warm air coming into the room.

2) The A coil and/or is seriously plugged and there is little air flow past it. Usually the A coil will freeze up under these conditions. Have you visually checked to see? Mostly when this happens little refrigerant is evaporated so your suction side pressures will tend to be on the low side. I suppose a TXV that wasn't working right could cause normal suction pressures in the face of a plugged evaporator.

3) Air in the refrigerant. This would cause close to normal pressures and little cooling. You've already ruled that out. Something to think about though.

Note: A TXV metering device (or just TXV) stands for thermostatic expansion valve. You should find that device inside the house on the end of the smaller liquid line. Just before it you should find the filter/drier in series on the same copper liquid line. They are usually mounted directly on the furnace just as the lines go into the A coil.

If I look on the LP and HP pipes on my outside unit thay are at the same temp, roughly 75ºF.

???????????????? its not cold and wet ?????

Originally the compressor red 90/250 but after coil cleaning the pressure dropped to 80/240. The problem is that the unit still does not cool.

This just dont work out :confused: :confused:
Head has to be higher some if the coil is way up there

ED ;)