Greetings,
I own a 2000 model F150 Lightning which has been very reliable for the past 20 years but the AC started to give me a problem so I'm looking for advice. The AC works fine, blows cool air through the dash vents when the truck is started but after some time, could be 10 minutes could be 30 minutes the vents quit blowing. I can cut the truck off and restart and most times the vents work again but quit after a few minutes. It acts like a vacuum leak but from what I can find online everything is electric controlled. If I leave the truck running and switch off the Ac then back on after a minute it doesn't fix the problem but if I switch off the engine and restart it usually corrects and works for awhile. Any help would be appreciated.

 

The air diverter doors are all vacuum operated.

Does the airflow divert to the defroster or does the airflow (to anywhere) simply diminish to almost nothing? Is there a change in the blower motor's perceived operation?

 

Welcome, where does it blow if anywhere when it stops out of the vents? Can you still hear the blower? Is it possible that the system charge is low and it is freezing the coil which stops the air? Do you see a large puddle of water under the truck after a while when it is turned off?

 

Blower runs on all speeds. If I put it on max cool it comes out the defrost vents. When it stops on its own I get very little air from anywhere. Not freezing up but I haven't put gauges on it to check pressures. Doesn't seem to be refrigerant related though. Yes condensation under the truck after running. I tinkered with it yesterday and found there are vacuum lines on the firewall so thinking that might be where the problem starts.
Much thanks for the reply!

 

That indicates a vacuum leak, probably in the vacuum circuit for the recirculate door's vacuum motor.

Bet it is... If the blower still seems to be running but there's no air moving, SOMETHING is blocking the airflow. An evaporator that is frozen into a chunk of ice is the usual cause. Your indication of the timing of operation to failure indicates this is the case.

The key is to look for an EXCESSIVE amount of water under the drain immediately after a failure event when the (presumed) ice melts. It is completely normal for there to be condensation from the system when operating. You have to look for the symptoms that are abnormal.

Bet it is... although it could also be due to a clutch that is not cycling due to either electrical or mechanical issues.