I have a 99 Exepidition Eddie Bauer. Everthing is fine with my a/c under the hood. The high side and low side check fine. When driving down the road with out warning the cold air changes to hot air. Seems to work better when you have it on max airbut not all the time. Sometimes you can turn it off then back on to get the cold air back again. Any ideas?

 

Do you notice a link between the temperature change and throttle position? I'm wondering if a small vacuum leak in the climate control system plus the normal drop in engine vacuum while the engine is being pushed might be a factor.

Ever notice air coming out of the defroster vents at inappropriate times?

 

Could also be a sticking a/c cycling/pressure switch.

 

I have talked to my daughter a little more, this is her Exepidition. This 1st started in Feb. She was driving home from our house about 20 miles away. She called to say her heater had quit blowing hot still blew air. I don't know if this helps you or not. I guess it would because this means that it's not just an A/C problem. I have had it down at the garage to have a leak fixed in the high side of the A/C line. They test drove it the morning and it happened to them. worked fine going out but switched to hot coming back in. They retested the pressure and all checks out ok.

 

Make sure that your ***** are not stripped. Mine did that after freezing for 60 miles finally figured it out. easy fix take the one off the rear control put it on the main control. Hope this fix your problem.

 

I have no *****. I have a EVAC system not ther manual A/C.

 

I have almost the same exact problem with my 98 expedition. The diffrence is the rear air works fine, it is just with the air in the front. I would have to keep it on max to keep the cold air blowing in the front, but it would still change to hot air sometimes with acceleration then I would have to turn it off for a few minutes to get the cold air back. Last week I started to notice that the air would stop blowing from the main vents in the front and start blowing out of the defrosting vents up front. It kept switching back and forth without me touching a thing. Now it will only blow out of the defrosting vent no matter what I have the manual control on. Hopefully someone here can help who has had this problem before. I took the truck to a local repair shop and they told me to take it to ford. I would hate to have to go there and pay a arm and a leg.

 

Are you sure it is not marginally low on freon? Will run for a while, then compressor is shutting off?

 

sounds like your blend door motor, being the evac system not *****

 

For the original poster: Have the blend door checked. It the arm is broken, the dash has to be pulled for replacement.

For the poster with air coming from defroster: Inspect the vacuum line that goes through the firewall. It is a black plastic line located between the firewall and the battery and commonly cracks or breaks at that location. A short piece of vacuum line makes a good splice repair.

Steve

 

Had same on 99 EB, read a thread to CK vacumn hoses behind battery and through firewall. found cracks in both hoses. Repaired these and no problems since.

 

Sounds to me like the blend door is broken. It is held in the cold position by an electronic actuator. If the blend door is broken like mine was, then every time I accelerated from a stop caused the door to swing to the hot position. I noticed this several times when I was at a complete stop, the ac worked fine. Step on the gas and I would hear a thumping noise(door swinging shut) and the air was hot. The acceleration of the vehicle combined with the air pressure from the blower would slam the door shut towards the rear of the air box and keep it in the HOT position. NOt good for me here in Arizona!. I replaced the door last weekend, tooke me 12 hours of labor and around 30 bucks for the door and I have COLD air all the time. The blend door is notorious for breaking according to a search in this forum.