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99.5 with strange AC issue

873 Views 2 Replies 3 Participants Last post by  toothless
my 99.5 F-250, 7.3 all stock

when the engine is at idle, and the tranny in park, it blows cool air. When the tranny is in gear, and the engine is turning 1900+ RPM it blows cool air. When the tranny is in gear and the motor turns less than 1900 rpm it blows warm/hot air, even if it is turning 1700rpm while going 65mph down the road.

What is this? Low Refrigerant? Possible vaccume line issue?

where to start?
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Sounds like low refrigerant. Or a clogged internal filter. OR a combo of both. I would take it to an Auto AC shop and have them purge the system, change the dryer and internal filter and charge it up. Ford's double o-ring seal for refrigerant lines has always had an issue where the pressure of the internal line flattens the o-ring a little and form a leak. You could try charging it yourself, but the new systems are far more sensitive to the newer freon pressure than the older stuff.
I am assuming, of course, that the ac compressor is coming on. But it should have a low-pressure sensor that will keep it from kicking on if the line pressure is too low. jmho.
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