Hello. I have A 91' 240 with 195k miles. It's getting to be summer down here in south Texas, and i've been using the AC in my car. I have recently noticed the compressor cycles on and off every few seconds. I assumed the ac had a low charge, so I went to Wal-Mart and bought one of those r134a recharging kits with the pressure gauge, coolant, and the thing you hook up to the coolant can.(forgot to mention, the AC was converted to r134a by the volvo dealer by the previous owner in 99') following the instructions, I hooked the gauge up to the fat AC hose next to the accumulator(low side). It read 100 psi, which was well into the red range on my gauge. Im assuming that this was the high side instead, or my AC was overcharged a whole lot by Volvo. If that was the high side, where can I find the low side of the system. If not, how do I get out the exessive coolant? Any other ideas on why my AC compressor is behaving like this(It still blows semi-cool air)? Any help would be greatly appriciated. Thanks in advance

If the compressor is not cycling during that time, you might see very high pressures especially if you just recently ran the A/C. On a hot day, as the A/C system balances out when you turn off the car, the high and low sides become basically the same thing.

To charge the system, the compressor has to be running. If it's running and you see a 100psi low side charge, there is a big problem like a suction side blockage, which is virtually impossible. But if the compressor was NOT running before, you should see more realistic low pressures like 20-40psi. A low charge cycle will yield suction side readings of around 25# and down.

It sounds as if the system was off when you were charging. If I'm misinterpreting your post, please correct me. It's unlikely you were hooked to the high pressure side as those pressures run well above 100.

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Chris Herbst
1992 745, 68k

And others:
93 944, 150k
90 245, 110k
88 744, 160k
87 245, 185k

Thanks Chris. I knew to run the compressor when you were charging, but didn't know it had to be running to test the pressure. Anyhow, it was low on coolant (with compressor running, about 18 psi) so I added a 4 oz can of polyol ester and about half of a 12 oz can of r134. It tests at 30 psi now and blows ice cubes. thakns again Chris.