AC Goes to Defrost under load
 

Hey Guys,

Have u ever experienced your a/c vent switch automatically from venting to you to venting through the defroster vent under load?

This has never happened before, I was towing a vehicle and started going up hill, when I gave it a little more gas the ac switched vents, when I let off the gas the vent went back to normal, ever since then it does the same thing, even when I punch the gas without towing.

I am baffled.

I plugged in the obd2 scanner to see if by any change any codes were tripped but no codes were tripped.

Any thoughts, Thanks

RE: AC Goes to Defrost under load
 

probably something to do with a vacuum hose or something that happened to me in my jeep and it was from when i drilled a whole in the vacuum canister under the bumper..it helped but it still did whta u explain and now its my sisters o i dont really mess with it anymore but if i had to guess thats what i would say

RE: AC Goes to Defrost under load
 

ive never heard of that before. i will look it up and c if i can find anything.

RE: AC Goes to Defrost under load
 

My dads 99 Ram did that. Its a vacuum leak somewhere that does it. I know an uncle of mine showed him what it was but that was about 7 years ago.

RE: AC Goes to Defrost under load
 

My 91 plymouth beater does that. It is a vacume leak. When the engine is under load, the amount of vacume it produces goes down, and with the leak, the vent control does not have enough vacume to keep the front blower engaged, and the air diverter slips backward into defrost. When the engine starts producing enough vacume, the air diverter moves back into place. For me it only happens when downshifting on a hill or merging onto the freeway. As soon as the RPMs drop, the front blower reengages. Engine vacume is also used to switch to the heater blower as well. I havn't had a heater in that car in two winters. [&:]

RE: AC Goes to Defrost under load
 

Great Suggestions,

Thanks guys, I guess I need to spend my weekend going through all the vacum lines.

If I find it, I will post a reply and some pics.

I wonder if deterioration of a hose would do it? I live in Arizona and I am thinking the heat might have something to do with it.

Thanks again! :)