"As stated you have a two speed fan and the first speed is almost always on if its hot out and you are using the A/C. It comes on when the A/C gets to a certain pressure (which it will always do unless you are low on refrigerant). "
Is that true for most/all models? The reason I ask is my low speed fans rarely come on and stay on, regardless of ambient temp. THey'll come on for 10-30 seconds and then go off. I'm pretty sure I'm not too low on R134a since they've behaved this way for years and the AC has always worked well. From what you say, sounds like they should be running fairly continuously. Might I have a bad pressure switch? How is it tested -- I assume by hooking up AC pressure gauges and seeing if the switch closes when the AC pressure gets to the set point?