I have a 1985 firebird, automatic trans, with a/c. Chevy 350. When I pull up to a stop light, the car stays put with my foot off of either pedal, unless I have my a/c turned on. This is very consistent. I can pull up to the light with the a/c off, let my foot off of both pedals(if the hill is steep enough) and I won't move, but if i just turn the a/c on, it will start rolling. I can turn it off and it will stop...

I wouldn't even know where to start, someone please give me a clue on where to start. Is this even a problem? I wouldn't think this is normal.

Thanks.

 

maybe the engine is having to work harder with the a/c on so it isnt able to keep its force of staying in the same spot... just a thought and i dont mean force just you know what i mean, idk really though

 

I was thinking the same thing. But I thought it might have something to do with the sprag or roller clutches in the transmission. its a 700r4, built by Monster Transmissions. Not trying to shoot down any ideas by any means, any response is accepted.

 

well i wouldn't have the slightest knowledge about any of that, sorry. if it helps your transmission is in a whole lot better shape than my 700r4 lol

 

You might consider a Monster Transmission, I paid 1300 for mine, shipping, and torque converter included. Check them out

 

Normal.

With the AC off, there's no added load on the engine. The idle speed that is set is enough to keep the car from rolling backwards.

With the AC on, there's an additional load on the engine that slightly lowers the idle speed, enough to where it's not enough to keep the car from rolling backwards.

This assumes that your Quadrajet idle speed isn't controlled by the ECU like an FI engine would be.

BTW, it's not good practice to let the trans hold your car on a hill like that. It creates excess heat that isn't good for the transmission.

 

Why would you not keep your foot on the brake while stopped? Otherwise you're just balancing the weight of the car against the convertor stall, which would be dependant on rpm, vehicle angle, and friction. Not a great way to hold it still.

 

I noticed it when I first let my foot off the brake to accelerate. I generally would not just suit there with my foot off the brake. But I did not realize it would be that big of a deal. I will take consideration of what you both have replied. Thanks for your help!

 

Also, how do you become a junior, senior, or supreme member?

 

Post! I think its currently 100 to lose your junior status, then 500 for senior and 1000 for supreme.

 

The carb has a solenoid that activates when the compressor clutch is engaged. It's purpose is to bump the throttle angle slightly to compensate for the extra load. It has a seperate adjustment from the regular idle speed, so you can dial it in so there is no change whether the A/C is on or not. Either the soledoid isn't working or it's out of adjustment.