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A/C compressor's clutch doesn't engage 900

posted by  940 4ever on  Thu May 20 14:46 CST 2004
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last visit: Wed Apr 21 11:04 CST 2010
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Today I turned on my A/C and found that the compressor's clutch doesn't engage at all. Does anyone have any idea? Any simple fix that I can try first before bring my baby in to the shop? Thank you








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    A/C compressor's clutch doesn't engage 900

    posted by  Volvodad on  Thu May 20 18:43 CST 2004
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    last visit: Thu Oct 23 16:18 CST 2014
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    The dashboard control unit is a weak point. The solder board and/or little relay that sends current to the compressor (via the low-press switch as brownboy said) can fail. Check at the low-press switch connector for 12V with A/C "on". If no 12V present, suspect a bad control unit.
    --
    Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD; plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)








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      A/C compressor's clutch doesn't engage 900

      posted by  940 4ever on  Fri May 21 12:34 CST 2004
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      last visit: Wed Apr 21 11:04 CST 2010
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      thank you. Since i am just a weekend amateur mechanic so I got a stupid question. When you saying to test the voltage for the low pressure switch, do i test it on the connector side or the accumulator side? Similiar question, if i wanna bypass the low pressure switch, Do I put the metal paper clip on the accumulator side or the connector side? Thank you








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        A/C compressor's clutch doesn't engage 900

        posted by  Volvodad on  Fri May 21 16:32 CST 2004
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        last visit: Thu Oct 23 16:18 CST 2014
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        I don't know the whole story of how this operates, but - - the blower fan must be on (even the lowest setting) and this enables the MCC unit to send 12V into the Green/Red wire when you punch the A/C button. This goes first to the Low-P switch on the receiver/drier, and if it allows, to the high pressure switch below the condenser, and if IT allows, to the compressor clutch, which then engages.

        So just probe the contacts in the Low-P connector with blower on low and A/C selected at the MCC panel. One of those contacts has to show 12V if the MCC is OK. If so, that's the wire from the MCC panel. The other wire will show 12V if the Low-P switch is operating OK and is not open-circuit because of inadequate refrigerant charge. And on it goes.
        --
        Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD; plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)








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    A/C compressor's clutch doesn't engage 900

    posted by  brownboy on  Thu May 20 15:53 CST 2004
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    last visit: Fri Jan 1 14:31 CST 2010
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    Look for the low pressure swich on the accumlator (on the passenger's side firewall, a silver cylinder shaped object with a/c hoses coming out of it); the low pressure switch is to the left rear. Take the connector off and use an unbent paper clip or a wire to bypass the switch. See if that turns on the compressor when the a/c is on. If so, you either have a bad low pressure switch or the system is very low on freon. If low on freon, fill the system and plug the switch harness back in and see if it runs. If the freon level is Ok then replace the switch.

    Hope that this helps.

    Mike
    --
    Mike Brown Greenville, NC 1996 965 105K 1994 940 135K 1986 244 137K








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      A/C compressor's clutch doesn't engage 900

      posted by  940 4ever on  Thu May 20 16:12 CST 2004
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      last visit: Wed Apr 21 11:04 CST 2010
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      Thank you for ur info. I got one more A/C question. I saw some oil stain near the color connector at the bottom of the radiator on the passenger side. Is it an indication of a Freon leak?







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