I've noticed that when I turn my AC on, the car lags down HORRIBLY. I even notice a lag with just defrost on, and no AC oddly enough. WHen I turn my AC on, my MPG drop by atleast 15 MPG and the car is almost unbearably slow. I have to accelerate at half throttle just to speed the car up decently. The air conditioning works great otherwise, besides the huge loss of power. I don't know what would cause this to happen, and I don't think it'* normal because on both of our Bonnevilles I noticed NO difference at all when the Ac is turned on, and when it'* off. The Aurora on the otherhand is nearly undrivable. I took it to the dealer just before my warranty was up, and they told me that the car was functioning 100% normal and nothing would be fixed. Occasionally, I will hear a rattling type sound from under the hood when the AC is on. It is not always there however. Any ideas? The video below shows how much power is lost from the engine when I turn the AC on/off. This was the best way I could find to show, because a video of the speedometer didn't really "show" what was going on, it was hard to tell a difference. By seeing the MPG gauge however, you can really see how much efficency is lost by using the AC. You can hear when I turn the AC on/off by the sound of the vent blowing onto my camera. I had the cruise control set at 50 MPH incase anyone was wondering what speed I was going. This was on a completely flat road, and the outside temperature was 97*. Let me know what you think.

http://media.putfile.com/DSCN0525

It is a quicktime video, so it will need to load 100% before it'll play.

I thinks its verys strange... If it were just the A/C lagging the engine I would think the compressor was on it'* way out or the electric clutch. But you say the say with the defrost. maybe you should try relieving the tension on the unibelt and see if the altenator spins freely. They can seize also and had one on a S10 do so to the point of tearing up the belt. What does your volt gauge do when all this is going on? With my altenator that seized, it got worse as I ran acessorys.

The AC compressor also comes on when defrost is set. It cycles the compressor to dry the air I learned. I can tell when it cycles on/off because the engine bogs down. The oddest part is that it isn't ALWAYS this slow with the AC on. Sometimes I'll drive almost normal, other times it is extremely slow. It doesn't make sense to me. Voltage is in normal ranges (high 14'*).

And the A/C will run if the temp setting is lower than cabin air regardless of the route chosen for the air to follow, When you said defroster I just assume it was with a warm setting. ( Now that I think about the summer weather... Duh )Well it sounds as though the A/C'* on its way out 88. I really cant see as how it could be anything else. And the Dealer stonewalling as your warranty expired sucks. I would take it to a reputable A/C shop and if it'* turns out the compressors bad, call the GM Customer Service and insist they eat the repair bill.

When the car is in park with the A/C on, does it sound like it wants to die because of such a huge load being placed on the engine? At a stoplight, what does the car idle like with the air on?

I think the strangest part is that it doesn't drive sluggish all the time. Does it only seem sluggish after you've had the A/C on a while, or will it do it immidiatly after you turn the A/C on?

Can't say I've ever hear of an A/C compressor siezing and causing so much power to be drawn off the crankshaft. I'm thinking that it might start to heat up after some use, start to expand, then all hell breaks loose as friction adds to the heating process. If that was the case though, I would think that something in the compressor would have had to give by now.

Good luck finding a solution and stay cool (esp when it'* 97* outside)

This is an interesting topic, Custom. One that I'm going to watch closely.

I've been having the same thing happen in our 99. I can't watch your video since I'm at work, but what your describing is exactly what I've got going on.

There'* no power down low and a moderate acceleration shift goes into the higher RPMs with the a/c on. It feels very sluggish. If I really get into the throttle, there'* power available, but only for another couple thousand RPMs.

I have brand new plugs, wires, air filter, fuel filter, and a clean throttle body. I have a funny feeling that the a/c compressor is creating a lot of drag due to age and miles (currently at 152,000). My fuel mileage hasn't decreased as bad as yours.

Does your belt feel hot after you've run the a/c? If so, it might be a sign that the belt is slipping on the a/c compressor.

What you describe sounds exactly w hat'* going on with my car! I have to rev it up to around 4,000 RPM in 1st gear to ge the same acceleration that I'd get at 2,500 RPM. It'* very slow feeling. It'* more sluggish when the AC is first turned on and the engine is cold, than it is when it'* been running for a while, and the engine is fully warmed up. i haven't been running my AC at all so I havne't really checked into it any more. I'll let you know once I use the AC again because it'* suppposed to be in the mid 90'* this weekend here.

What does your car do at idle with the A/C on? Does it seem to idle like mormal? Try revving the motor up in park with the A/C on and see if it doesn't rev as freely as it should.

I have a crazy idea that the computer might be seeing that the A/C is on and be commanding a higher shift because of the A/C load, only it'* command way too high of a shift. Are you really laying into the throttle when your at 4k acceleratingwith the air on?

With the AC on, the idle is normal all things considered. The engine does not have a hard time idling as far as I can tell. With teh AC on though, I can hear a rattling sound coming from under the hood. I get teh same rattle on/off when I have it set to defrost as well. The rattle goes away if I turn the climate control to vent, or off. Also, the shift points are much higher because I have to give it a lot more throttle to accelerate at the same speed when I have the AC on. I also have noticed that the transmission shifts much more firmly/rough when I have it on. It'* really odd..

Custom...this is crazy! I think we have the same car, but with different body panels. I couldn't have described my symptoms any better. Mine are exact.

I'll try gently free-reving it with the a/c on. I'll report back with my findings.