I have this truck with the 5.4 liter motor with 121,100 miles on it. I have a question about my A/C…It blows very cold while im driving but when it is idling or i accelerate from a stop, it blows warm for a few seconds and then turns cold again. So is this a problem or normal? Thanks for your help.
I think you have a vacuum leak somewhere in the HVAC system. The air temperature blend door (probably controlled by a vacuum actuator) is moving when you accelerate, allowing incoming air to go through the heater core rather than the AC evaporator. When you ease off the throttle it moves back to where it was and you get cold air again.
The fact that it blows warm at idle puzzles me. Idling and steady driving should be about the same, since neither requires much throttle opening. Have you had the refrigerant level checked?
You make a good point for the pressure test, but I think you were right with the first guess, the vacuum leak.
If I had to bet, I would bet that this vehicle has an electrically-operated blend door. If so, vacuum is not a factor. When you say accelerating, does that mean wide open throttle? If so, I am not surprised. I bet this has an AC cutout at WOT.
Warm at idle could simply mean that the fan is not blowing at high speed, the condenser is clogged or charge is low.
Your truck does have an electrically operated blend door. A vaccuum leak will not have any effect on it. I would say low charge.
Low charge. Absolutely. At idle, there’s not enough refrigerant being handled, not enough pressure to cool the air. The reason it’s still hot RIGHT after accelerating is because there’s a few moment’s lag before the pressures stabilize at the higher RPM and the rush of refrigerant reaches the evaporator core, plus time for the air passing over the core to get cold.
BUT! Take it to an A/C shop and have them put it on a manifold gauge. That’ll tell.
-Matt
Alright thanks guys for your help. I’ll either recharge it myself or take it to an A/C shop. Ill update ya on this. Thanks a lot again.
Rusty