Engine Size: CAT C15
I am having an intermittent AC problem. Most of the time, no problem; however, sometimes in heavy traffic conditions, AC starts blowing 'HOT' air. Have replaced the compressor, dryer and had system evacuated and recharged, no improvement. I am at a loss as is my mechanic. Any ideas as to what to check? Of course, it does not do it when I get into a shop.
When it does it, it would be useful to pull over and check if the compressor is engaged or not. Obviously inconvenient to do this on a big truck. Since you've replaced the compressor, failing to engage probably isn't because of the clutch gap (a very common problem) but it could be the relay or one of the other electrical controls.
If the radiator fan is not working while you're in traffic, the condenser will overheat rapidly causing an overpressure that shuts down the A/C. This will be apparent long before the engine starts to overheat.
If the compressor and fan are engaged but still no cold air you could have a balky TXV that sticks closed. Pressures would have to be measured while the problem is occurring.
And finally if the air coming out is REALLY hot, it could be a problem with the system that selects between heat and A/C and the two are fighting each other (the heat will always win). This wouldn't be it if you have the heater hose valves closed off for the summer though.
Edited: Tue June 23, 2015 at 7:38 PM by mk378
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