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Old 07-14-2012, 06:39 PM
ArtNJr ArtNJr is offline
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Join Date: Jul 2012
Location: Western N.C.
Age: 62
Posts: 240
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Vehicle: 1998.5 Dodge 2500HD 4x4
Trim Level: SLT Laramie
Color: Black
Engine: 1998-1998 359ci (5.9L) Cummins ISB 24-valve Diesel I6 235hp 420lb/ft (manual), 215hp 420lb/ft(auto)
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Originally Posted by ramalamadingdong View Post
140000 miles

Truck was parked for seven years. Began driving it again two years ago but never checked AC until two weeks ago and no cold air. Had it serviced then left on a 1000 mile trip and noticed that the cold would stop blowing when engine was under pressure such as going uphill. Otherwise is blows very cold.

Any ideas?
No doubt there is some sensor that's turning the A/C compressor off when the engine's under load, but I couldn't tell you specifically what on that vehicle. But for example, when I went to an A/C mechanics seminar years ago they chose a Ford Escort as an example car -- if you put auto trans fluid in the power steering pump (which was always the standard) instead of newer, lighter PS fluid, the A/C would never get cold. The car's engine had so little torque that it couldn't run the PS pump under load & the A/C compressor both, so when you'd make a tight turn into a parking space, etc., a sensor in the PS pump would trigger the A/C compressor to shut off & putting heavier fluid in the PS unit made that sensor detect a higher load all the time.

And newer A/C compressors are not designed to run all the time, they're supposed to turn on & off periodically. But I'd bet there's a load-sensing device somewhere that "tells" the A/C compressor to turn off when the engine's under a heavier load -- if you could get a factory service manual you could probably find out where it is too.
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