far_cry wrote:i ask air conditioner technician about this thing and he told me that the max pressure you can get is 300 psi
you know thats not a refrigerator compressor so he can make low temp
The AC tech would have no idea what the pressure capability of the pump is. In an AC system the pressure is largely limited by the liquefaction pressure of the coolant. For the various freons (R12, R134a, ...) that isn't all that high.
If two cooling systems use the same refrigerant I would expect them to operate at about the same pressures. An AC unit using R12 and a frig using R12 would be operating at about the same pressures since it is the coolant that determines the optimal pressures. To get to lower temperatures the frig will need to have larger heat exchangers and a larger volume
pump. Note that the max pressure
of the pump is not really related to the size
of the pump.
The AC compressor is definitely worth a shot. Be careful though, even if it "only" reaches 150 PSIG that represents a hell of a lot of energy even in a small reservoir. The pump may well reach much higher pressures.
BTW, car AC units generally operate with the "low" pressure side at 25-50 PSIG and the "high" pressure side at 200-250 PSIG. Those pressures are set by the amount of refrigerant in the system, not by any limitations of the pump. So it looks like a car AC will do at least
150-225 PSIG differential between inlet and outlet. I would expect a window AC unit to be similar.