air conditioning question

the other day i noticed my a/c wasnt blowing as cold as it did a month ago. i hooked a set of manifold gauges up to the system and the high side pressure was about 150 psi below what is should have been and the low side was down about 10. I thought it might be low on freon, so i hooked a 12 oz can of 134a up to the gauge set and tried charging the low side. There was hardly any suction and it took about 20 mins to get half a can in. The pressures didnt go up either, so im assuming that my compressor is bad. Anyone else have ideas? I dont want to spend 200 bucks on a new compressor to find out it wasnt the problem. Also, i retrofitted the ac system to 134a the year before. the car is a '90 buick lesabre limited. thanks for the help!

Hook the gauges back up and rev it up a little. See if that 10 psi on the low side goes into a vacuum. I'd probably guess you have an orfice tube that is starting to plug up.

i hooked the gauges back up today. when i revved the engine, the high side pressure did not change, but the low side dropped an additional 10 psi below the already low reading. I was down to 20 psi when i should be at 40. When the car is idling, the low side sits at 30. When i retrofitted to 134a, i did not drain the compressor oil. I just let the system suck in the oil that came with the retrofit that is supposed to neutralize the oil for r12. at the time of the retrofit, i did not think that the old oil had to be drained, but i now know it has to be. i think once the old oil mixed with the 134a, it fucked up the compressor. any other thoughts?

So the high side is 150 and the low side is 30 ? How hot is it where you are at ? The oil should should be compatable. Before I would change the compressor I'd drain it down and open the lines and replace the orifice tube and refill.Now high pressure will vary with the temprature of the day.There is actually a formula for that like a number plus the temp of the day should equal high pressure ....but of course i forgot it.....lol. But if it's really warm where you are 200-225 high side is not uncommon.

sorry, i was a little unclear. The high side was 150 psi below normal. I had a table that told me what the pressures should be at each temp. The high side was at only 50 psi and the low side was at 30 psi. The temp was about 83 degrees ferenheit out when i checked the pressures. it would be nice if it were the orfice tube, since i dont want to blow 200 bucks on a new compressor. Where would it be located?

It is in the line going from the condenser to the evaporator. Check out the lines at the connections look for a spot in the lines with some indentations about 3 inches away from the nut. I have also seen them at the firewall going right into the evap. But with the pressure at 50 and 30 the compressor is probably shot.