My Wife's 98 Protege stalls at idle when the A/C is turned on. There seems to be an incredible drag on the engine. If I keep the RPM's at 2,500 without the A/C on and then switch it on, it drops to about 1,250. Then stalls if I come off the gas. Any ideas as to the problem? I think it has to do with the compressor, but I don't know how to tell.[/align]

 

Sounds like it may actualy be the ISC. I had this issue with my '97 Protege and took it to a dealer who "fixed" the AC. That was not the correrect diagnosis (it was fairly expensive too). The problem was finally solved when we got the air induction system cleaned (which includes the ISC valve). Try cleaning the valve with some throttle body cleaner and check to see if the air filter needs replacing as well as the air intake hose.

 

Excellent starting point that 93greenstrat pointed out. Always start with the easy and inexpensive first.
If your IAC valve is not operating correctly you will also have a low idle with electrical loads of headlights, rear defroster, and interior fan on high as well as cranking the P/S to full lock all at the same time. These will create a load for IAC to compensate for as well. If idle is compensated for adequately then try turning the very front part of the A/C compressor ( with engine off of course ) by hand. It should turn with only moderate resistance. If it is very difficult to turn and other loads were compensated for ok then it would then be time to have the compressor/system pressures evaluated.