for a/c to work efficiently, a fresh supply of air needs to go through the condensing coil, a/c on in traffic probably isn't going to work very well.
the temp of the air coming out the vent should be 39*..this is going down the road.
think of refrigeration this way, it doesn't make anything cold, it removes heat..the condensing coil (in the grill) is a heat exchanger, if its really hot out side or no air can take away the heat, your a/c will suck.
sounds like the high side switch on some on these cars may be bad...but 134 isn't as forgiving as the old r-12..
let's give nuke's a chance..