AC Excessive High Pressure

[mback12000]

Just picked up an 03 AV, service history unknown but only 40k miles. AC working but weak and compressor cycling. Hooked up gauges and added a bit of R134a, compressor stayed on and started to get cool but the high side gauge was over 300psi. So out of guessing I then replaced the accumulator and orifice tube, added 2oz of oil, vacuumed for 45min and started adding refrigerant. When I got to about 15oz added the compressor stopped cycling off and she started to blow cool (50deg vent thermometer) but the gauges read 42 low side, 355 high. The system is supposed to take 1.8lb (29oz) so with only 15oz added it isn't overfilled. What's wrong? FYI, these pressures are on a 60-65 deg day. With the vehicle off gauges show about 73psi on both low and high.

 

[mback12000]

Well, I let the thing sit about an hour while surfing the web for answers. Came back, started the truck and gauges read normal. Added another can of refrigerant and she blows 45 deg out the vent, gauges 28 low and 160 high, with ambient temp about 60. So it magically fixed itself. No idea why it was so high with a partial fill.