I HAVE A 1999 F-150 86,000 MILES AC COMES ON FINE BUT WHEN I CATCH A RED LIGHT OR STOP AND GO TO TAKE OFF IT STARTS TO BLOW HOT AIR INSTANTLY ALMOST LIKE THE HEATER WAS TURNED ON. IF I TURN THE AC SWITCH OFF AND THEN TURN IT BACK ON IT WILL AGAIN BLOW COLD MAYBE 5 SECONDS OR MAYBE 5 MINUTES THERES NO TELLING HOW LONG BEFORE IT DOES IT AGAIN. I TOOK IT TO THE SHOP THEY HOOKED THE AC MACHINE AND SAID THE PRESSURE AND FREON LEVELS WERE ALL PERFECT. THEY KEPT IT IN THE GARAGE FOR OVER 45 MIN. WAITING TO SEE IF IT WOULD ACT UP WITH THE MACHINE HOOKED UP I TOLD THEM IT ONLY DOES THIS WHEN YOU ARE STOPPING AND GOING AND NOT EVERY TIME. HOWEVER I HAD TO LEAVE AND GET MY DAUGHTER AND NEVER GOT ANYTHING DIAGNOSED OR FIXED AND IT'S GETTING HOT HERE IN FLORIDA. I WOULD GREATLY APPRECIATE ANY HELP.

 

Hopefully it is not your compressor...those are not cheap. I wish I could help out my fellow woman! You may try searching those symptoms on google.

 

I had the same thing happen to a Ford E150 van. It turned out to be the vacuum controller for the heater/AC.

It's a pain to work on and can be something as simple as a pulled vacuum line or as complicated as the controller.

Find a savy mechanic who you trust to work on it.

BTW, I was reading some other posts and it seems the "Blend Door" is another culprit on these vehicles. Either case I'm pretty sure the dash needs to come out.

 

If it is in stop and go traffic and the compressor is running it may not be getting the air flow across the system. I had someone whating to recharge a system that had the right pressure on it when we checked it he had a bad e-fan. At highway speeds the ac had plenty of air flow across the condenser to cool but at a stop it had none. Just another suggestion.

 

I second the blend door suggestion. It seems to be a very common problem and yes the dash does have to come out to replace it. P.S. Its going to be 95 degrees here in Central Illinois on Saturday, Sunday and 97 degrees Monday.

 

mine does this when i step on the gas real hard and accelerate fast... is this the same thign ur talking about?

 

No, You Don't Have Accelerate The Gas Hard. It Don't Do It At Every Time I Stop But Enough To Be Real Annoying. And It's The Heat That Is Coming On Until I Turn The Switch To Off And Then Turn It Back On To Max Ac. Another Thing Is If I Manually Turn The Temp. **** To Warm It Stays Cold The Heat Does Not Come On.

 

It's your blend door. I had the same problem in my F-150. Hit the brakes, and the door swings forwards, and you get cold air. Hit the gas, the door opens, and you get hot air. It's a cheap part ($30), but the labor will kill you. Plan on spending about $500.