This started about three months ago and has gone from infrequently to happening very often now. When the truck warms up and I am running the a/c even at idle it is very cold. When I start moving under accelleration it continues to blow very cold. If I get off the throttle and coast it seems to start allowing some of the hot air from the heater core box to enter the syytem. When I put my hand by the vent you can feel there is cold air coming out, but it feels and smells like some of the air is coming from a different place. Also, if I have an extended idle time it does the same thing. Sometimes, not always if I apply alot of throttle I hear what sounds like the blend door shut and the air becomes very cold again. Other times the only way to get cold air again is to turn it off for 3 to 5 minutes while running and then turn it on and most times it starts to blow cold. Do you guys think it is a weak Vacum Pump or a Blend Door failing or maybe something else? My truck is a 2004 F250 Super Duty Powerstroke. Thanks

 

Sounds like your system might be low on refrigerant. Have you checked it?

 

Yes, system was just serviced and is up to spec. Thanks

 

If it was "up to spec", it would be working, wouldn't it?

 

I agree. Sounds like its low.