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A/C problems no more! 900

posted by  turboman on  Fri Oct 29 13:19 CST 2004
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last visit: Sun Jul 15 02:38 CST 2007
[RELATED]

A couple of times in the past month I have aske for help with my A/C compressor cycling very rapidly. I had replaced the low pressure switch (pressostat), because the original one had failed causing the compressor not to come on at all. The new switch allowed the compressor to engage but cycle at a fast rate. I had the vendor send me anouther new (volvo oem) switch. It did the same thing as the first one.

After checking all leads and following all advise, I found and ordered an aftermarket switch not connected with volvo in any way.

IT WORKS! What are the odds that I got two bad pressure switches? I'll be making a nice call to the first vendor Monday mornnig.

Good weekend,
Chris








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    A/C problems no more! 900

    posted by  someone claiming to be sredwine on  Mon Nov 1 06:26 CST 2004 [RELATED]

    Turboman,it seems highly unlikely that you got two bad switches.You probably have the wrong pressure (too low on 'low side'-low refrigerant).The factory switches will not allow operation at too low a pressure-your aftermarket one may be set to allow a lower pressure.Running the syetem low on refrigerant (AND oil) can damage your compressor!Get it checked.You can buy a cheap recharge/pressure test kit at most auto parts stores for around 20 bucks.Let us know whay happens-good luck! sredwine 94 940T 151K








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      A/C problems no more! 900

      posted by  turboman on  Mon Nov 1 06:49 CST 2004
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      last visit: Sun Jul 15 02:38 CST 2007
      [RELATED]

      Thanks for the comments. I had been fighting this thing for more than a month. I evacuated and recharged the system to ensure the charge was perfect to the ounce of factory fill. Both Volvo OEM switches would cycle off on low pressure (cool day, fast idle) at around 25-30 psi, then they would cycle on and off again at essentially the same pressure of about 32 psi. There is no deadband built into those switches.

      The pressure range on the aftermarket switch is engraved on the side of the switch: Off at 1.7 kg/cm2 and on at 3.1 kg/cm2. This corresponds to about 24 and 44 psi. My gauges confirm this. It cycles the compressor off at around 25psi and then back on at around 45 psi just like it should.

      The place where I got the first two switches either sent me the wrong switch twice or there is a bad batch of Volvo pressostats running around. I'm not having a good time trying to tell the seller (previously reputable) all this either.

      Chris







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