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Air conditioning erratic

I have a 2001 SAAB 9-5 SE, with 70,000 miles on the odometer. Two weeks ago, while driving with the AC on, I became aware that the air flowing from the vents was no longer cool. (It wasn?t heated, just ambient temperature. The outside temp was 98 degrees.) Then I noticed that the engine temp needle had fallen to the bottom of the scale. I immediately turned off the AC. The car was running fine, and there were no warning lights on, but the temp needle stayed pegged to the bottom of the scale. This seemed so odd that I pulled over and turned the engine off. I checked under the hood, found no loose vacuum hoses, no fluid leaks or anything else out of order, so I re-started the engine. The temp needle quickly moved to the middle of the scale. I turned on the AC, and it blew cold air. Two weeks of driving with the AC on in temperatures between 90 and 100 degrees followed, with no problems. Then, this weekend, the same combination of no AC and the engine temp needle at the bottom of the scale happened twice, with a new twist–the second time, the “check engine” light came on. It stayed on two days, during which I did not use the AC. It went on again when I started the car this morning, but the temp needle moved to the middle, and I had to drive 200 miles through 100 degree weather to get back to Reno, so I turned on the AC. Cold air! Then at some point about halfway through my trip, the “check engine” light spontaneously went out. What’s going on? How can there be any connection between the AC and the engine temperature gauge? And what about that engine warning? Any info or advice would be much appreciated. Many thanks.

Apparently you do a lot of driving at high speeds (over 70 mph). This will cause the amount of Vacum to drop if you have a leah in the Vacum system somewhere.When the Vacum drops off the Blend Door will drop to heat even if your heater is not on.
You have a vacum leak somewhere and it can cause all sorts of wierd problems.
Take it to a mechanic and have the Vacum system checked out.

Thanks for the suggestion. I’ll get it checked for a vacuum leak. However, I’m still puzzled by the apparent link between the AC failing and the needle on the engine temp gauge falling to the bottom of the scale.

I agree, it sounds more like an electrical issue.