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jeep AC banging!!

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  • jeep AC banging!!

    2002 grand cherokee4.0 engine,i tried the ac a few days ago and it was really low so i added some 134,the cooling improved some ,BUT it sounds like a machine gun going off,im thinking its in the ex valve as it will continue for a short while after i shut the car off,its bad enough that it shakes the suction hose!,ive read a couple places where a new ex valve cured their problem like this,,and no its not overfilled !!
    anyone else have this problem?

  • #2
    Welcome. Still need some info like pressures before and after adding refrigerant. Just why did you think or "know" it was a low charge and now "no" it's not overcharged? If it leaks as most would have or an elusive one where is it leaking.

    These were known for weak evaporators almost want to ask when it was done if you know or just did?

    Where is this banging if you know? Chances are the compressor is the moving part it's that. Next is why still to find out but pressures first at what temp and RPMs please,
    Tom
    MetroWest, Boston

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    • #3
      the reason i know its not over filled is at idle its shows about 30# on the low side,when its reved up the pressure drops to around 20# and the compressor kicks out like normal,when you shut the car off the banging continues for a while even after the compressor has long stopped turning,also if you switch the compressor off it will continue for a short while,it sounds like a machine gun going off,i didnt hook up the high side gauge!,which might raise some questions??,this doesnt sound like a compressor noise to me,its really loud

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      • #4
        Could you be describing refrigerant popping out the high pressure relief valve? Some compressors have these valves to protect the system.

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        • #5
          i have a Dakota i changed over to 134,it was popping the relief valve,this sounds different than that did,,its strong enough that the suction hose vibrates when it happens

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          • #6
            Start over there's no info saying this isn't grossly overcharged the only way is evacuate all refrigerant and fill to spec. My chart (they can be wrong check for spec under the hood) for a Grand Cherokee is just 27oz of 134a. So easy to add and blow relief valves you didn't know it needed any at all did you?

            It's not just some color gauge of what it should be for pressures rather the complete algorithm of the RPM at what temp and what load on the system. Temp coming in thru the grille and temps out center vents of dash.

            134a is very unforgiving to be off in this 2.7oz or 10% if spec is accurate would begin the failures.

            Converted system more of a rethink don't compare that at all.

            Again, start from a well held vacuum and charge the exact weight. Then and only then at the assorted loads, temps are the pressures credible and should match with expected performance.

            One more: If this has blow oil all over the place now have to consider this may be quite low on oil can't know exactly without starting from then a total flush out but if seen and not known when any if any was added is guessing only. Guessing either of these too far off can and will just destroy the system quickly or soon after messing with it and it seem it's been messed with enough,
            Tom
            MetroWest, Boston

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            • #7
              im gonna pull a vacuum 2moro and see what i see!!,stay tuned!!

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              • #8
                We've lost easy archives above on some pattern failures some by brand of vehicle. Basic rules of charging I'll post a link it's a mile long just to read is the crude basics. Start from a well held vacuum and know it! Charge (purge air out of hoses!!) the exact weight if know. Shocking how many system can just snap to working with just that. LINK HERE > http://autoforums.carjunky.com/Autom...YSTEMS_P45460/ <

                Not said there is if it doesn't last take note of how long it took to leak down is the #1 reason still for the first problems. Finding leaks is another whole game on this just put your finger under the drain tube or Q-Tip it. If oily you know it's the common evaporator leak but too old now it should have already failed long ago maybe just me but don't hear of a second one as weak as OE ones were,
                Last edited by Tom Greenleaf; 05-24-2019, 12:52 AM.
                Tom
                MetroWest, Boston

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                • #9
                  I have been trying to think what would fit all of the symptoms reported, The hard one to fit is the continuation once the vehicle is shut down. I am leaning toward a serious over charge, with liquid refrigerant entering the compressor. Once it hits the hot compressor, rapidly expanding into gas. It is the only thing that would continue after shutdown. Still it doesn't explain everything.
                  The banging can be a clutch or belt momentarily slipping when the compressor is "slugged" with liquid.
                  Still, there is plenty of room to discount my reasoning. More info and perhaps a video of the system in operation with a gauge manifold attached would help
                  Last edited by Cornbinder89; 05-24-2019, 01:58 PM. Reason: spelling

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                  • #10
                    ok,heres the latest,i pulled a vacuum overnite with my robinair dual stage pump,then i added two 12 oz cans,and part of another can,the high side will get to around 150 when the engine is revved up,the low side will drop below 30 to around 20 and the compressor will cycle off till the low side comes back to around30-40 ,the suction hose sweats clear to the compressor,the lowest the cabin air will get is around 50 if its revved up sitting still,the high side hose/pipe at the accumulator,is NOT hot,the outside temp is around high 70's with really high humidity,the banging is gone!!!im thinking its compressor time,along with a ex valve and accumulator,however what AC skills i had have mostly been forgotten over the years of non use,,SO HELP!!

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                    • #11
                      Tom says the spec is 27 oz, so if you trust the cans, which is not a good idea, two cans plus 1/4 of a can would be close to the 27 oz. I would say you were way over-charged and were "slugging" the compressor with liquid refrigerant. You are lucky to not have done serious damage to the compressor.
                      Pressure DOES NOT tell you if it is correctly charged, it tells you the temp of the refrigerant at the point measured.
                      150 psi high side = about 112 deg or around 35 degs over ambient temp passing thru the condenser, so not bad and with in what would be considered acceptable.
                      Low side cycling and sweating to the compressor indicates that the refrigerant is leaving the evaporator at close to freezing, and the compressor is cycling off to prevent evaporator from freezing.
                      Until proved otherwise, I would assume that the system is charged close to the correct amount, and any lack of cooling is cause by the air handling, either air is bypassing the evaporator, or a air door or coolant (heater) control is not working properly and allow heat back into the air stream.
                      I don't believe you have a compressor problem, nor any other refrigerant related problem.
                      Strap a thermometer or a IR thermometer on the suction pipe from the evaporator as close to the evaporator as possible, I think you will find it plenty cool, but for some reason, it is not cooling the air going to the vents,

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                      • #12
                        these jeeps are known to have a blend door problem,and the air doesnt seem to blow as hard as i think it should,i have it set on recirculate and havent looked to see if all the doors are working correctly,thanks for all the help!!,ill let you know if i get it fixed,im NOT going to pull the dash to get to the evap core!!,way to old and fat for that!!

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                        • #13
                          I know how you feel, that is why I stopped working on cars 20 years ago. Most older big trucks are easier to work on, the new ones not so much!
                          If Jeeps are known for blend door problems, that would be my 1st place to look. Your not getting the heat into the refrigerant
                          Unless you have a leak at the evaporator, I see no indication that it is at fault, Not much other than leaks to go wrong with an evaporator.

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                          • #14
                            ? Doesn't blow air as strong. Sure a blend door not fully moving you might be able to see the actuator for it under-dash. Other is plain dirty some with easy blower motors just go in there see the garbage all built up clean depending on what type of what. OIL wouldn't be nice. If it blows well without A/C and does that slowly that's a strong clue it's icing up. If any performance worth a dang A/C should drip to the ground. If not but works just not so great look for a huge puddle when parked that was the iceberg it was making.

                            I doubt it but oh my - check if this has the cabin filter? I plain don't know if offered or not some of these are luxo-boats just might have one. Some folks choose to just take those out being nasty to do. Can't know that one look in owner's manual should cover possible features like that,
                            Tom
                            MetroWest, Boston

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                            • #15
                              My Cab-over trucks have a filter before the evaporator, like a house type filter 12x10x1! To get to it you have to pull the air suspended passenger seat, as the seat base is the top of heater box.
                              I think looking into air delivery is the correct action to take, regardless if it is a clogged filter, bad blower or blend door, it is all part of air delivery and for now, we can leave the refrigerant side alone.

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