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A/C Compressor cuts off at 2000rpms or above 700 1990

posted by  '90 740GL on  Mon Aug 11 19:34 CST 2014
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last visit: Tue Aug 26 19:00 CST 2014
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Hey everybody!

I have a 1990 744 with an air conditioning issue. I have converted it over to R134a about 3 months ago, and it has been running great ever since. About a week ago, I noticed that my AC wasn't working on the interstate. After further driving and examination, my AC only works at 1900rpms or below. Above 2000 rpms it does not work. My compressor clutch wheel stops spinning above 2000 rpms, and will slowly turn with some slight screeching or grinding noise. I saw some fellow volvo owners tried the shim fix on their compressors with some success. The earliest model that I have read about that working on is an 850. I raised the rpms until the compressor clutch wheel started to lock up, then pushed on it with a broomstick to see if it was a shim spacing problem, but that did nothing.

Does anyone have any idea why my compressor locks up and slowly turns above 2000 rpms?

Thank you,

Ben








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    A/C Compressor cuts off at 2000rpms or above 700 1990

    uid 55's pic
    posted by  john sargent on  Wed Aug 13 18:53 CST 2014
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    last visit: Wed Oct 22 09:07 CST 2014
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    It could be with higher RPM the low pressure switch cuts the compressor out. The low pressure switch is in series with the compressor. It's design intent is to not allow the compressor to run if there is no refrigerant (and therefore no lube) in the system. Running a compressor with no lube will burn it up.

    You can use a test light to see of the low pressure switch opens above 2000 RPM. If the switch opens above 2000 RPM, just add some refrigerant.
    --
    john








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      A/C Compressor cuts off at 2000rpms or above 700 1990

      posted by  '90 740GL on  Thu Aug 14 17:40 CST 2014
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      last visit: Tue Aug 26 19:00 CST 2014
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      Thank you for the reply! I just took the connector off of the low pressure switch & ran a jumper wire across the connector's two contacts. That should override the low pressure switch & make the compressor stay on, correct?

      After that I revved the engine up & the compressor still locked up above 2000 rpms. I've now done this & pushed inward on the clutch wheel when it is locked up. No luck with either.

      Does anyone else have any ideas?

      Thank you,

      Ben








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        A/C Compressor cuts off at 2000rpms or above 700 1990

        posted by  Amarin on  Thu Aug 14 18:17 CST 2014
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        last visit: Thu Oct 23 22:42 CST 2014
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        Hello,

        There's an air gap between the clutch and the spinning compressor pulley. The gap should disappear when the clutch is on, pulled by magnetic force to stick with the spinning pulley. When this happen did the gap reappear or not?

        If the gap reappear then you may need to adjust the gap and/or clean the magnetic coil (compressor wiring) wiring contact so that full electrical power may be sent to the coil.

        If it does not (i.e. there's no gap when the clutch locks) then your compressor may have lubrication issue. As you've mentioned you just converted to R134a many months ago, the next question would be - did you or the AC shop use correct lubricant for the conversion?

        Plus, like aleekat mentioned, did the R134a was weighed in during recharging?

        Regards,
        Amarin.








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        A/C Compressor cuts off at 2000rpms or above 700 1990

        posted by  aleekat on  Thu Aug 14 18:11 CST 2014
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        last visit: Fri Oct 24 13:19 CST 2014
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        Did you actually measure how much 134 you put in? Unlike freon, you can overfill the 134 system.
        --
        Post Back. That's whats makes this forum work.








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          A/C Compressor cuts off at 2000rpms or above 700 1990

          posted by  '90 740GL on  Tue Aug 26 18:15 CST 2014
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          last visit: Tue Aug 26 19:00 CST 2014
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          Hi everybody! Thanks for the advice! The R134a was filled up to the correct amount. I fixed the problem the other day, and wanted to update everyone!

          Looking at my compressor, I found the ground wire connected to the rear tensioner bracket was loose. The rear bolt on the compressor tensioner had loosened up. I tightened it up & everything was good to go again! The compressor runs at all RPMs!

          Thank you for all of the suggestions!

          Thanks,
          Ben







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