I had a friend replace the compressor and everything else related to the air conditioning system. It seemed to work fine in the beginning, but now the AC only works when I'm driving on the highway. At a stoplight, it blows warm air. Driving slowly only gets a tiny bit of cooler air.

Did he hook something up wrong?

 

Since it seemed to work fine at first, but has slowly gone bad, I would suggest you contact your friend again, and have him check the pressures on both the suction and discharge side of the compressor. Either the system is low on refrigerant, or there is a partial blockage in the condensor assembly (the one by the radiator) ....

 

That was quick, thanks. I'll let you know what we find.

 

Or the cooling fan is not engaging when the A/C clutch kicks in, which means that the condenser is only getting the heat removed by the fresh air running across it from the car being in motion.

Please post pressures and indicate if cooling fan engages when A/C is turned on....

 

The cooling fan did engage when the A/C was turned on. One shop told me the compressor needed to be replaced, however when I drove away the A/C worked perfectly!
The next day it didn't work anymore. I took it to the Saturn Dealer and they replaced everything, again.
As always, they were nice to me. That's worth something.
The bottom line is that we don't know what went wrong. Saturn said it was a defective compressor but didn't say why.