MORROW5

My AC blows cool air fine at idle through all vents like it is suppose to,When I give it a lot of gas for more then 10 sec. or so under load meaning drive down the road and not letting off the gas the AC switches from all vents to just the front defrost vents up on top the dash. No one I know has ever heard of this. Hopefully someone out there has HELP it is getting hotter and hotter around here. thanks.........

Davescort97

It's a vacuum problem. The switching doors use vacuum through a vacuum motor. When you give a lot of gas and put it under a load the vacuum gets so low the door on the A/C goes to defrost. The reason for this is because of a safety factor. Whenever something goes wrong with your heater A/C it automatically goes to defrost. Check for loose or missing vacuum lines at the motor or at the heater A/C controls. From what you describe there is a canister that holds enough vacuum to work your controls when you have the engine under a load. Either the vacuum lines have come off it or the canister is rusted out etc. Check for what looks like a can with a couple of rubber hoses going into it. If you can't find it under the hood (usually mounted on a fender well) check under the right front fender well.

UsedtobeSmart

I agree with Davescortguy97. My old Lumina wouldn't blow out the vents at all when I was driving if I had my foot on the gas and eventually tripped a random check engine light. I had a leaking brake booster is what it was, but it took me six months and a lot of green to track it down because I didn't know what was causing the problem. Check everything you can for a leak. Most likely it's the reservoir already mentioned, but if that's not the culprit, don't stop there.

DonSor

In addition to the possibility of vacuum problem, the AC system I believe was also designed to temporarily disengage during quick acceleration to reduce the load on the engine needed in fast take off.

MORROW5

Thanks for all the info I did a quick and I mean a quick look and could not find what I was looking for but I will look very close this weekend. This is a 99 ranger and I did not see a lot of vacum lines? I looked on the fire wall and fenders but no canister? Thanks again and I will post my findings.

DonSor

If you have a vacuum leak no matter how small you will more than likely get a Check Engine Light indication such as "lean" on one or both banks.