When A/C stops cooling, the coolant temp gauge goes up. What's causing what?
 

1997 SL. A/C compressor was replaced last year. This year, most of the time, A/C is working, but it cuts out occasionally. When it stops cooling, the coolant temperature goes up, or at least the gauge goes up. Seems that most of the time it cuts during short hops around town. Which is causing which?

Well, if the thermal switch that turns the fan on and off is inoperative, the only way the fan will run, is if you set the A/C on, and turn the air control to recirculation (max). The A/C will override the thermal switch, and make the fan run as long as the A/C is on. If you turn off the A/C, the fan will stop. In driving around town with the A/C off, the wind through the radiator is dependant upon the speed of the car. When stopped at a traffic light, it will tend to rise .....

I should have stated that I'm not switching the A/C on or off myself. While the switch is on it's cutting out on its own. It just blows as if it were on vent.

saturns will do this (AC cutout) by design when the load on the engine is extremely heavy--which doesn't sound like your situation.

recommend taking it to someone who knows saturns to sort it out

Do you have a set of A/C gauges for automotive use (R-134a) ?? If not, then you need to swing by your dealership, and have them look further ......

I'm taking it in this week. Like clockwork, the A/C is fine when I'm cruising on the interstate, but if I get in a traffic jam or do errands around town, it usually stops cooling and the coolant temp gauge gets close to the critical point. Often if I turn the blower off, the A/C switch off and turn the ignition off at a store, it will be fine when I start up again -- but I'm not certain the turning off of switches actually corrects the problem. Could this be a thermostat issue?

Could it be the engine coolong fan ... it should always be on when the A/C is on, and running.

+1 On the cooling fan -- bet the darn thing is like totally inoperative ....

if that were true, the engine would run just as hot with the A/C engaged as it would with the A/C physically turned off, no? The fact that the coolant temp does not rise when the A/C is engaged tells me the engine cooling fan is OK.....

I think the key here is that when he's on the highway, everything works OK, but when he's in traffic, things heat up and quit ....