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  • A/C questions ...

    One thing that I really don't have a good troubleshooting/repair understanding of is auto A/C systems. The BWB had the a/c light flashing on the control panel .... I reset that and it fired right up. It was cool out (highs 50's/ low 60's) when I did that .... air seemed cool.

    Today it's in the 80's, so I turned on the A/C. It worked good letting the truck run in the drive. I headed out, dropped Stewie at school and headed to the bank. As I was leaving the school, the A/c started blowing hot air. I got home and popped the hood, the compressor was not engaged. If I jump the connector at the pressure switch, the compressor will run but the A/C still blows hot.

    Is something plugged up?

    I have access to a dual gauge a/c manifold set, but what am I looking for when I hook it up?

    How do I tell if the system has already been converted to R134?

    Thanks guys ...
    Whiskey for my men ... and beer for their horses!

  • #2
    There are better A/C experts than me, but my two cents is it definitely sounds like a low charge. You can tell if it's been converted over to 134a by the fittings on it, sometimes only on the low pressure side. Only a true hack would install the larger 134a fittings and remove them after charging the system. The gauge set you have will either have 12 or 134a fittings. Probably 134a fittings, if it's used on newer vehicles then certainly 134a fittings. They won't fit on a 12 system, so you'll know if you have a 12 system.

    Personally, I'd vacuum the system and see if it holds. If it does, pump it full of freon and a bit of oil, maybe some dye, and try it out. I did this with my '87 Jeep by installing the 134a fitting over the 12 fitting on the low side, but I didn't do the vacuum part! The A/C worked good on it too for the following three years, and worked great the day I quit driving it.
    Escaped on a technicality.

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    • #3
      You have a low psi switch, if its to low it opens and kicks the comp out, look for leaks oil with dirt stuck to it.

      If the high side is way high, and the low side goes into a vac, you have a orfice tube or a expansion valve stuck closed, if you have both equal and the comp is running the expasion valve is stuck open. if the low side is slightly high and high side is real high then the condencer may need cleaned or the fan on it not working, it cant get rid of the heat. Its real easy to know if you have gauge readings and or a site glass.

      High pressure expands and takes on heat. Like spraying starting fluid on your arm. as it expands from the can it expands on your arm and cools by taking on heat

      the orfice tube or expansion valve control the ristriction and or expansion of the fluid taking on heat in the evaporator in the car, the comp moves it to the condencer to get rid of the heat it has taken on. Simple
      2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
      First to run in the .90s .80s and .70's in SBN/A
      2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
      2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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      • #4
        That I understand .... thanks Jeff.

        So what am I looking for as far as gauge readings? I would really like to learn from this, instead of just throwing parts at it and hoping something sticks. I do have a friend at a body shop that can vacuum it down and charge it for me.

        When the compressors shoot craps, do they usually make noise or will it still run quiet?

        Any thoughts on flushing the whole system?
        Whiskey for my men ... and beer for their horses!

        Comment


        • #5
          low pressure should be in the low to mid 30s 25 they kick out on the low side gauge and the high side is a result of the heat taken out 200-350 depending on the heat of the day.

          Comp shoot its breaks a shaft or the gauge reading will be off or leak fluids
          Last edited by JeffMcKC; May 10, 2012, 02:14 PM.
          2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
          First to run in the .90s .80s and .70's in SBN/A
          2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
          2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

          Comment


          • #6
            Two things, find the leak or the comp took a shit.........If the low side pressure is higher than 70 you probably have a clogged orifice tube, if the low side is equal to the high side pressure the comp took a shit.......
            Last edited by TC; May 10, 2012, 05:08 PM.

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            • #7
              80 degrees and needed AC. What a puss.LOL.Too many years spent in a cop car with the AC running and wasting taxpayers dollars.Toughen up ButterCup.LOL.BTW I changed my phone number and where I live. LMAO!

              Comment


              • #8
                While not the problem here, something to be aware of: the High pressure switch cuts the compressor off when the pressure gets too high. "too high" for R12 isn't high enough for 134a, and the gauges will tell you if the switch is cutting off the compressor too soon. I got 10 or 15 degrees cooler air by changing my switch.
                ... if someone will help me out here with the numbers. The mechanic who helped me with the A/C on the Blazer told me the numbers, but I can't remember them.

                Okay... maybe my mechanic was wrong or perhaps I am remembering it wrong, because I can't find anything to support what I just said up there about the pressures needing to be higher to work as well... but I did swap out the pressure switch and it stopped my compressor from cycling non-stop.

                This link, if correct information, should tell you about everything you want to know about automotive a/c systems. http://www.griffiths.com/achelp/achelp3.html
                Last edited by yellomalibu; May 10, 2012, 07:38 PM.

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                • #9
                  Originally posted by ksj2 View Post
                  I changed my phone number and where I live. LMAO!
                  It won't help Don .... the black helicopters were already dispatched!
                  Whiskey for my men ... and beer for their horses!

                  Comment


                  • #10
                    .... And I found this too: http://www.manexcorp.com/images/Bus_Guage_TS.pdf

                    It seems to break down what the gauge readings mean, and as yellow'bu said, if it's correct info.
                    Whiskey for my men ... and beer for their horses!

                    Comment


                    • #11
                      Got the gauges and hooked them up. Compressor cycles this morning w/out needing to bypass the switch. Al;so, it's only in the mid 50s today.

                      WITHOUT the engine/comp running, they read 65/low and 70/high

                      ENGINE/COMP RUNNING, 110/low and 140/high with the comp cycling off and on regularly

                      Sight glass is not full with bubbles steady and present

                      So from what I gather, its probably just low on refrigerant. No signs of leaks but then again, everytime I was the truck i spray off the engine. I'm thinking since it's an unknown system (it has been converted to 134 by the fittings) that maybe a flush and new o-rings are in order before the re-charge ....

                      thoughts?

                      EDIT: and now that I see what I posted, the high reading on the low side is all wrong .... correct?
                      Last edited by Bamfster; May 11, 2012, 10:20 AM.
                      Whiskey for my men ... and beer for their horses!

                      Comment


                      • #12
                        110 on the low ( suction side) ? if low on freon, the Low side will be very low when the Compressor is running.
                        Reading , Pa
                        Good Guys rodders rep.
                        "putting the seat down is women's work" Archie Bunker.
                        Ban low performance drivers not high performance cars .

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                        • #13
                          Yep^^^^^^ if its cycling how high does the high side get? It may have a high side switch and be over charged. If you need to jumper it to make it run long enough to see also test with the blower on next to high speed.
                          2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                          First to run in the .90s .80s and .70's in SBN/A
                          2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                          2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

                          Comment


                          • #14
                            Comp running .... switch jumpered...

                            Low side is 90-95

                            High side is right on 100

                            No noises coming from comp (I knopw that doesn't always mean anything)
                            Whiskey for my men ... and beer for their horses!

                            Comment


                            • #15
                              Does it have a expanision valve? if so it could be stuck open,

                              or the comp shaft is broken maybe. I would check the shaft first. With the engine off try to spin the front hub thats hooked to the shaft. Comp make some noise even quiet ones.
                              2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                              First to run in the .90s .80s and .70's in SBN/A
                              2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                              2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

                              Comment

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