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AC cooling ok but intermittently..recently recharged

Discussion in 'General Chevy & GM Tech Questions' started by So Cal 1999 Silverado, Aug 31, 2013.

  1. I have a 1999 Silverado LS I am the original owner. . Recently the AC would stop blowing real cold air, after first turning it on, but would blow cool-ish air. If I shut off the AC for a few mins., and then turn it back on, it would blow cold but eventually back to only cool. I did this on the recent trip for 2 hours of freeway driving. I took it to tire and repair shop and they recharged it. It seemed to work ok for one day and now it was back to the same old thing. I don't recall ever recharging it since I owned it brand new. It seems to be worse at freeway speeds. There is more but let me start from here. Any help?
     
  2. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    When you turn the AC on, does the compressor clutch engage?

    If it does not engage, the next step will be to check the refigerant pressure to see if it is where it should be.

    If the compressor does engage, the next step will again be to check the pressures to see what kind of pressures you have.

    While most professionals will have a nice manifold pressure kit that will allow them to monitor both high and low side pressure simultaneously, you can (or at least could a few years ago) get an inexpensive 134A pressure gauge from a parts store like Autozone that would allow to check these pressures. If you are serious about diagnosing AC by yourself, you will need a pressure gauge/gauges at some point.

    Here's a decent chart with expected high and low pressures for a typical auto AC system. http://idqusa.com/faqs/r-134a-system-pressure-chart/
     
  3. Thanks Mr. Shorty. The AC was recharged and the tech said all pressures OK.

    I had the system recharged and he said he put in a dye to test for leaks. He also said all of the pressures were good but I did not ask for a measurement. The clutch does engage when you first turn the AC on. I don't know if the clutch is engaged when the AC is not blowing cold. I did not check for this while at idle or parked.
     
  4. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    The dye will cause any leaks to show up under a black light. If there is a leak, this will hopefully help locate it.

    If the compressor comes on when you first turn the AC on, that means there is some pressure in the system. Low pressure cut off is typically around 25 psi. So it looks like the next step is to see if the compressor runs continuously or intermittently, and what the pressures are doing.
     
  5. dedmon27

    dedmon27 Rockstar 100 Posts

    Thanks for the pressure chart link shorty that solved my problem. My high side was 425 low side was 125. I just replaced my accumilator, orffice tube and compressor, took it to my mechanic at work to recharge. The shroud said 1.8lbs but on the machine he put 2.25lbs so I'm assuming that was the problem. I'll have to call him and tell him. He wants me to put a condensor in it but when you blow thru it with shop air it is fine. Plus according to that chart if it was blocked it would be reading to low on the low side right?
     

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