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AC stops blowing cold air while driving. Works good if truck interior is cool while stopped, but as soon as I take off, it stops blowing cold air....Takes forever to cool truck after interior get hot. All pressures are correct. Does not ice up. Could this be a vacuum issue and how would one troubleshoot this? Vent controls work correctly and vacuum pump is working and will cycle no and off.
 

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"resident smarty pants"
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The vacuum only plays a role in the blend door operation and in the valve that stops flow to the heater core.

Check to see if the vacuum line has become disconnected from that valve. It is located near the firewall in the "passenger-side/center" location.

https://www.powerstroke.org/forum/general-6-0l-discussion/172680-control-valve-after-service.html

That said, generally when that is disconnected you default to the defrost mode.

You might want to see if the degas bottle is over-pressuring.
 

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I've had other vehicles that showed they were charged but after draining & recharging worked great. Just an idea. A few cans of refrigerant from walmart isn't much.
 

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I've had other vehicles that showed they were charged but after draining & recharging worked great. Just an idea. A few cans of refrigerant from walmart isn't much.
If The system is stagnant, that can be true, but run the ac with the gauges and it's a very different story.

Also, if it were undercharged, he would have the opposite symptoms. Warm while idling and colder when reving.

The water valve is a good thought too, but vacuum isn't related to rpms on a diesel. The function of that valve shouldn't have anything to do with how fast he's going.

Its a weird one, but the high side pressure is definitely where I would start. Does anybody know if the AC in these trucks have a high pressure switch? I know some do for sure.
 

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Mine blowed hot when I over charged it. It was cold at first but the next day started down the road and nothing but hot air. Got a new gauge and hose and it showed overcharged. I let some out and got it in the right area and it's been cold ever since. My gauge was bad..

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My town car did that right before the compressor locked up.
 
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