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post #1 of 3 Old 07-07-2014, 12:23 PM Thread Starter Fanatic
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AC Problems

Hi Guys,

So when I turn on my truck, I usually let it run for 5 min to let the cab cool down, and the motor warm up before I get my wife and son into the truck. I just noticed twice the last few days, that the AC only blows warm air unless I get into the truck and start driving it.

Is there an issue with my AC system, or do i need a tune that increases the idle? I tried revving the motor, and it does not do anything, if I put it in gear, and give it some power, cooling starts and works fine. If I park afterwards, and let the motor idle it still cools. It only happens when I start the truck, right off the bat it sometime wont cool till I drive. Any help would be great.

Owner / Operator: Mike
My Truck: 2001 F350 | 7.3L PSD | 4R100 | Crew Cab | Short Bed | 4x4 - 233,000 miles - 1 Year of ownership
Mods: Swamps High Voltage High Frequency IDM | Air Raid Intake System | 4" Straight Pipe Exhaust | BFGoodrich KO2 33in Tires
Usage: Tow Pig
Tow Toy: 98 Fully Built Toyota Rock Crawler & 1996 Skeeter Bass Boat
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post #2 of 3 Old 07-08-2014, 12:45 AM
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When was the last time you had it serviced (or did it yourself)?

I would not increase the idle to fix this issue - the A/C should be reasonably cold at idle (like low 30's at the vents, AC on max, full blower, with the vehicle under a shade and not heat soaked) - even at first start after a few seconds to get the system up to speed (so to speak).

Heat soaked you could expect it to take a longer time to get to that temp at the vents on max, but it should still get there in a few minutes at the most. Check temps at the vents and then if not at stated above, I would troubleshoot by doing the following:

1) Clean the A/C coils at the radiator - get all the crap out of there checking for clogged passages. Those will affect A/C in a big way. Let radiator dry before next step. (Wet radiator will increase cooling and you don't want that yet.)

2) Check for obvious leaks - easy to identify by a build-up of dirt/oil residue at the connections of the system. If present, have system drawn evacuated - replace o-rings as necessary, service properly.

3) Start vehicle and turn AC to Max - check temps - if not at low 30's in about 2 minutes - go to step 4 - else, system is fine. Watch compressor - is the clutch cycling on and off rapidly? If yes, try bypassing the LOP switch (I believe these vehicles have one, but I don't have my schematics here to verify) After bypass, compressor clutch should stay engaged. If it does, you are probably low on freon and the system cannot build pressure. The clutch should keep the system active for a long time on start up on a warm day without bypassing it.

4) Now, run hose over radiator - check temps as you do this. If they drop inside at the vents, you probably have either a clogged set of coils (which you shouldn't if you cleaned them properly) - or are low on freon (R134a).

5) If nothing else found, have levels checked - service as necessary.

You state it gets cool as you increase engine speed - that pretty much rules out the compressor being bad - so you are looking at clogged coils or low freon. My money is low freon.

Hopefully others will chime in to make additional suggestions and make corrections to what I suggest.

Good luck to you sir!

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post #3 of 3 Old 07-08-2014, 11:08 AM
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It's sounding like low refrigerant, not able to build enough pressure& heat soaked enhances the problem. Put gauges on it & see where the low side pressure is at. Or throw a can in & see what happens

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