'91 Deville AC = Acceleration?

[barbquebutt]

My '91 Deville has been having problems with its AC system. Lately when I turn on the air conditioning or front window defroster, it causes the car to accelerate. I'm not sure how much because I've been more concerned with not hitting the car in front of me than testing the glitch.

I've had problems with the AC before with it not cooling very much or at all. But now it seems that its hard to get warm air flowing.

At first, I thought it was maybe the throttle sticking, which it might be...slightly. But that problem just causes it to not slow down, not accually speed up.


Any theories from you fine people?

[caddydaddy]

When the A/C system is engaged, the computer has the idle speed controller motor raise the engine RPM's to compensate for the power loss from the A/C compressor. But since your A/C compressor is not working, and not putting an extra load on the engine, it's just causing the extra throttle position to speed up the engine. So until you get the A/C system fixed, it will do that.

[barbquebutt]

would that affect it even when the whole system (fan, a/c, etc.) is off?

[caddydaddy]

Originally Posted by barbquebutt

would that affect it even when the whole system (fan, a/c, etc.) is off?

When the A/C is off, the engine goes off the normal idle presets, so the idle should be at normal speeds when the A/C is off. Idle speed for the 4.9 should be around 600-650 RPM's.

[ilgoldstein]

Since the defroster is supposed to turn on the compressor, you will get that effect. I never noticed that happening with my 93 when the air didn't work, so you might have a faulty throttle control solinoid.