Don't know what to think...

[smasher]

I can't figure this out. When I get on the throttle, the fan slows down (heat & A/C). If it's only set on low, it shuts off. If it's on hi, it slows down in discrete steps, just like the speed settings. It does'nt happen in neutral, only while driving. The lights and radio work fine so I don't think its the alternator. Almost like the ..., no I don't know? Anyone seen this before? How about the solution? Thanks,

[Whamhammer]

Probably what is going on is that as you accelerate, your rpms increase and that increases the speed of the water pump. Also the faster you drive, the more air is supposed to flow to the radiator. The computer is probably programmed with this in mind, so it backs down current to the fan to take advantage of these aspects.

[smasher]

I don't recall that happening in the begining. Does yours or anyone else act tlike this?

[JayTA98]

I heard of Fords doing this to get more advantage of HP but not sure in our vehicles. I know mine doesn't do what you describe.

[Whamhammer]

I don't recall that happening in the begining. Does yours or anyone else act tlike this?

I'm just thinking on the theoretical. I know that GM takes into account the vehicle in motion for cooling by aerodynamics. I've never really checked it. I think my '89 did. For a while, I put a remote fan control that I tuned the switch to engage the fan at a lower temperature than the normal setting (because I was in a lot of stop and go). I ended up removing it because the switch kept shorting out. You might want to talk to a Chevy shop and make sure its normal or not.

[Sleeper101]

Sounds like you have a vacuum leak. Take some carb cleaner while the car is running and spray it over all ur hoses under the hood.

[smasher]

I like this answer. I did use the HyperTech programmer and made a lot of changes; thats how it's been for ten years now. I'm not aware of an option like that, but maybe it's automatic? Many trips to the track (Rte. 66 Joliet) and I never noticed the effect until recently.

[smasher]

I think this solution has the highest likelyhood. And I like your method for finding the leak. But is there some single vacuum leak that can actually cause this effect?

[67CamaroRSSS]

At WOT the AC compressor is shut off by the PCM (declutches) so the engine doesn't over rev it and destroy it.

I noticed it here in PHX at the track. Sitting with the car idleing keeping me cool. Run down the track and all it does is blow hot air.

That's why high horsepower solid lifter engines back in the Muscle Car days were not available with AC.

[Z28_Driver]

Interesting observation. I have never noticed this problem, but I ususally don't have the ac or heat on when I go out to drive the car to death.