A/C problem - Ford Powerstroke Diesel Forum

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post #1 of 8 Old 08-08-2006, 08:13 AM Thread Starter
bob
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Question A/C problem

Marc,
I have an A/C problem and you seem to have addressed other A/C problems in the past but nothing that fits my symptons.
I have a '99 350 Powerstroke that will cool fine when the temp is cool and when the motor is cool, but about the time the engine reaches running temp the A/C quits putting out cold air. If you leave it on, it will come on occassionally and blow cold for a few min.
Freon checks out full. Engine is not running hot.
I've cleaned the coil and radiator. Noting that some ( maybe 20%) of the fins on the coil are bent from commerical truck washes.
Any suggestions where I should start??
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post #2 of 8 Old 08-08-2006, 11:20 AM
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Re: A/C problem

The first thing I would check is when it stops cooling see if the compressor clutch is engaged and the compressor is turning. If it is not then it might be held out by a pressure switch (high or low). To see what it happining a set of gages on the system is needed.

hope this helps
Jim

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post #3 of 8 Old 08-08-2006, 11:39 AM Thread Starter
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A/C problem

Yes, the air compressor is shutting down, just dont know why. The freon checks ok and it blows cold air for a while. I just got a set of gages.
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post #4 of 8 Old 08-08-2006, 03:35 PM Thread Starter
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A/C Problem

Further checking with gages. Could not get the compresser to come on today so placed a jumper wire from battery to the compressor. Came on and has 45lb.pressure on low and 225 on the high side. Blowing cold air and maintained as long as compresser forced to stay on with jumper wire. Tried a wire at the high pressure switch and the low pressure switch but would not stay on without the direct to battery wire.
Is there a curcit braker that could be failing? My fuse panel does not show one.
Any suggestions?
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post #5 of 8 Old 08-08-2006, 04:43 PM
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re:

I don't have a diagram for the 99's but, the 2000's have a relay controlling the compressor that is run from the PCM. It shows a fuse in the central juction box feeding power to the relay to operate the clutch. Maybe some of these other guys have the right diagram for that year. It looks like the pressure switches feed a signal to the PCM. I'm just looking at block diagram with not too much detail.

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post #6 of 8 Old 08-08-2006, 05:10 PM
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Yes, there is a relay for the AC compressor and that sounds like your problem....if you cant find a schematic that shows it, let me know....ill track down which one it is for you.....
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post #7 of 8 Old 08-09-2006, 05:40 AM Thread Starter
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A/C problem

No, I don't have a schematic for the truck and would appreciate any help to fine this. I thank you in advance for your help.
Bob
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post #8 of 8 Old 08-09-2006, 05:50 AM Thread Starter
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Quote:
Originally Posted by gbear
I don't have a diagram for the 99's but, the 2000's have a relay controlling the compressor that is run from the PCM. It shows a fuse in the central juction box feeding power to the relay to operate the clutch. Maybe some of these other guys have the right diagram for that year. It looks like the pressure switches feed a signal to the PCM. I'm just looking at block diagram with not too much detail.

Jim
Thank you Jim. So the pressure switches only feed a signal to the PCM not a direct connection to the compressor. That would explain why my jumper wire across them did not acomplish anything, but the direct to bat did. If I can find where that relay is located I may have found my problem. Thank you greatly.
Bob
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