e150gt - it's my belief the evaporator would start freezing up b4 you ever got 33 degree vent temps.

different refrigerants yield different pressures.

a good set of gauges is your starting point. i'm assuming your fans work as intended and the condensor is free of dirt/debris.

refrigerants as a rule of thumb boil at approx. 20 degrees below zero. i say boil, in other circles the term evaporate is used. evaporation attracts heat and the first principle of a/c is that heat moves toward cold. the hot air in your car is drawn to the evaporator under the dash - magnetic sort of affect. next stop -> compressor where the heated charge is pumped up even more. eventually the juice gets to the condensor where the heat is expelled. there are a few other parts i left out - just doing a high level thing here.

bottom line - the refrigerant and evaporator act as a heat magnet and the condensor acts like a radiator - expelling the heat.

the mastercool book tells the whole story.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"