Sorry... I'm in some heavy duty training classes for my "other" work... I've been on and off the board.

I'm pretty sure of one thing: One can of 134 (12oz) MIGHT cause the comp to kick in, but it would be very quick to shut off again. Twelve ounces isn't even 1/2 charge.

Now, I am experienced in A/C work. Especially on Volvo. Not an old timer by any means, but a legitimate A/C tech. Unless I'm totally missing something here, I don't see how it would be possible for the compressor to turn on at 30 and shut OFF at 45 on the suction side. You're absolutely sure that the compressor clutch is engaged during that period of time? The system will gain pressure on the suction side if the compressor is off, beacuse of heat exchange from the cabin (if you are removing heat from the cabin, that is).

Something seems odd about the whole thing to be honest with you. I can't help but think that the pressure readings aren't right (i.e. the comp might not actually be running). If you have verified the compressor is actually running, then I'm at a loss as to what would make the low pressure go UP when the compressor runs. That would be almost impossible, especially if it shuts off when the system's pressure elevates. That is exactly the opposite of what it's supposed to do, obviously. I sense that perhaps the pressure readings are in error (not necessarily the numerical reading, but the conditions of the system) and that there is an electronic fault somewhere causing erratic or non-functional conditions outside of the pressure circuit.
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1992 940 wagon, 72k
make people envious; smile often.