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  1. #1
    Sr. Mechanic poncho62's Avatar
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    Sep 2013
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    Hanover, Ont, Canada
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    Default Air conditioning question

    Last summer I had work done on my AC system...97 GMC...New compressor, dryer. , top pipe and valves....Had it charged. Worked good. Today, while waiting for the wife in the store, I thought I would crank it up to circulate the compressor etc. The compressor wouldnt kick on. It is about freezing here (32F). When I got home, I bypassed the pressure switch on the dryer and it would kick on. I am thinking that my system has leaked the refrigerant out.
    I tried my wifes van and her compressor isnt kicking in either.
    Question....Is it because its too cold out or do I have a problem in the spring when I need it.

    [B]1997 GMC

  2. #2

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    what are your pressures with the compressor clutch disengaged? generally that is not cold enough to keep it from kicking on in a properly charged/ working system.

  3. #3
    Sr. Mechanic poncho62's Avatar
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    Default

    Dont know...I havent any gauges to check it.

    I have been told that it should also cycle with the defroster on in colder weather, which it is not. More evidence that it may be low?

    [B]1997 GMC

  4. #4

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    Even a fully charged system there may not be enough pressure in the closed loop system at 32*F. Since this is the first winter since the rebuild and it's been very cold, a fitting may have leaked in the extreme cold due to contraction. You'll need to wait until it gets to about 65*F before you can get an accurate pressure reading and any good A/C tech usually wait for warmer weather to "top" off the refrigerant. At cooler temps they'll put in enough to get the system to work because too much and the first hot day the pressures can get too high, cause damage and the high pressure switch (if there is one) will open the circuit to the compressor.

  5. #5

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    Do you have a heated, or underground, public parking garage that you could leave it in for a couple of hours. Let it warm up and then test it.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  6. #6

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    If memory serves correctly, the low pressure cutoff switch is set for about 25 psig (40 psia). The vapor pressure of 134A is 40 psia at about 40 F, according to engineering toolbox: http://www.engineeringtoolbox.com/re...rt-d_1683.html I would expect below 40 F that there is not enough pressure in the system to engage the compressor clutch. If you feel you need to test the system, you will probably want to warm it to 50+F at least.
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    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

  7. #7
    Sr. Mechanic poncho62's Avatar
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    Default

    Thanks guys...I will wait until spring to check it out...no heated shop and its -20c (0f) here these days

    [B]1997 GMC

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