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Thread: I need help with AC troubles

  1. #1
    Registered User
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    I need help with AC troubles

    This is my problem. The AC compressor shuts off unless the fan is on high. If he outside temp is upper 80s or more, it will shut off after a while even on high fan. If it is 70's it will stay on for all fan speeds. It is like as the freon temp goes up on the suction side the compressor shuts down. Is there a sensor in the system that could do that? The freon pressures are ok and the compressor seems to work ok while it runs. It may need new compressor but I hate to do that if it is a sensor causing the problem. Thanks, Jon

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    There are two switches and a relay that controls the power to the compressor clutch. If you have gauges i would monitor the pressures when the compressor shuts down. If the pressures are high you could have a radiator cooling fan issue, don't know if you have OE fan or electric??? but electric fan not operating properly or fan clutch issue could cause high pressures.

    AS far as switches There is a high pressure cut-off switch on the stem to the high side charging port. That shuts down the compressor at a predetermined pressure to "save" the compressor from over pressure. Could be week and causing your issue. It could be jumped if pressures are OK to test. There is also a low pressure cut off cycling switch, can't see it, it is on top of the suction accumulator, "receiver dryer" That could be week and shutting the system down.

    Could have a relay going bad or even too much air gap on the AC clutch or a bad AC clutch coil, opening under heat.

    I would put a test light directly to the ac clutch connector and see what happens when it shuts down, If you loose power try jumping the high pressure switch, easiest to get to then the low pressure switch. Don't remember if there is one or two relays in the system could have one to shut down the compressor under wide open throttle also. Thee trucks are getting old and anything can fail, so you have to look at everything!!!

    Hope this helps, if you get more info or need more help I can dive into the wiring diagrams if necessary. I doubt that the compressor is the issue though, they don't pick and choose when to work!!!

  3. #3
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    thanks, I will try a few tests. the clutch could be a problem as it has over 460,000 miles on it. I had the controller apart last night and replaced the o rings on all four of the vacuum solenoids that were leaking. under power it would switch to defrost because of the vacuum leaks at the switching station. YouTube is a wonderful thing!

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    Quote Originally Posted by Jonkaase View Post
    thanks, I will try a few tests. the clutch could be a problem as it has over 460,000 miles on it. I had the controller apart last night and replaced the o rings on all four of the vacuum solenoids that were leaking. under power it would switch to defrost because of the vacuum leaks at the switching station. YouTube is a wonderful thing!
    yes I would agree I know our shop would be lost without YouTube for sure!!! Many times if the clutch gap is too wide with a lot of wear it will separate when it gets hot. If that is the case you can easily adjust the air gap with out removing the compressor Just remove the nut on the shaft and pull the clutch outer disk no reason to remove the belt or any of that remove one or two spacer washers and reinstall the outer disk and nut.

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    I jumped the high pressure switch, no change. I did watch the clutch and it clicks off and you can see the gap when it is on low fan, but only when you give it some throttle. I just took some shim out and will try it on the way home. ... Thanks

  6. #6
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    C1008 is the relay for the Ac compressor, it is under the hood in the relay/fuse box. There is no relay as such for wide open throttle cut out, but I believe that is handled directly by the PCM. the clutch relay is a smaller relay. There are many more of those one is for fog lights and for trailer wiring. Simply switch with one of the others. There is also a diode in that box for the compressor clutch it is the center diode of three at far end of box, if relay doesn't do anything you could try that. Also may seem simple question but what temperature do you have the control head set at?? And also does the MAX air setting make a difference???

    The next thing and possibly the cause would be the AC cycling switch mounted on the top of the accumulator.

  7. #7
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    Thanks for all the help. The clutch adjustment may have fixed it. I drove 33 miles on low fan at 85 outside temp and it never cut off. Before it would have qiut 5 minutes in. Jon

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  9. #8
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    That' great, easy fix!!! seen that a few times on high mileage vehicles. The air gap gets too wide from wear and the magnetic coil gets week with age and heat and it just can't keep it engaged. Good work!!!!

    GOOD FOR ANOTHER 500,000 MILE!!!!

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