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Odd A/C Problem

Discussion in 'Stock 2002 - 2005 Explorers' started by TechGuru, June 7, 2018.

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    1. TechGuru

      TechGuru Well-Known Member

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      I'm usually the A/C guru around here but this has me stumped, I've never experienced this on anything before.

      The a/c is perfectly cold, most of the time, I've noticed lately my compressor cycles a lot while cruising down the highway and and creating enough load to feel it in the vehicle movement.

      I hooked up my gauges and the low side is normal but the high side is hitting 450psi at 2800rpm.

      Normally I would think clogged orifice tube but when I've experienced those on the past the low side was low. This is acting more like a over charge, but it was last charged 2 years ago when I replaced the compressor and it was fine the last 2 summers and nothing has been added since.

      Condenser fan roars at cold start up and after sitting running in the heat for a while so I'm pretty sure the fan clutch is good.

      As I said before it's cold "most of the time" there are 1 minute periods where it starts to get warm I'm guessing once the high cut out switch has been triggered and it takes a min for the pressure to go down enough to come back on...

      I looked it up, high cut off is at 430psi and cut on is at 285psi. Just in case anyone coming across this thread would like to know, the low cut off is 25psi and the low cut on is 44psi.


      According to this http://www.chiltonlibrary.com/content/images/Ford/S3N/S3NC0007.pdf that high of PSI is normal if it's 120 degrees out. It was about 100 degrees when I tested.
       
      Last edited: June 7, 2018
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    3. blabla

      blabla New Member

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      Too much oil? (Just a wag)
       
    4. TechGuru

      TechGuru Well-Known Member

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      But how would that just now be a problem? The system has not been opened (caps not removed for anything) in two years...

      I did notice something weird, as I revved it up to 2800rpm the low side went down as it should but then it rose some then went back down, that makes me wonder if someone installed one of them variable orifice tubes in it.
       
    5. blabla

      blabla New Member

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      Just another wag: what if the condenser is partially plugged? The pressure would rise above the cutoff before adequate refrigerant had been cycled - essentially reducing the capacity of the system. I think the net result would be increased cycling. Like I said, just a wag as AC systems are not my forte.
       
    6. Joe in NY

      Joe in NY Active Member

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      Could just be the compressor retiring and clogging the orifice strainer or condenser..
       
    7. BrooklynBay

      BrooklynBay Moderator & long time member. Staff Member Moderator Elite Explorer

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    8. plasticseng

      plasticseng Active Member

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      Is there plenty of airflow across the condenser? Too little airflow will result in high pressure on the high side with somewhat normal low side pressure.
       
    9. Donystoy

      Donystoy Active Member

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      Was the refrigerant properly weighed into the system when it was worked on two years ago. If it has worked fine until now, and you have no mechanical noise my gut feeling is that there is an issue with the compressor again. Not sure on the type of valving used on these type of compressors. I know that r134a does run at higher pressures than r12 did but am not familiar with expected head pressures. With automotive there are a lot more variables involved so 450 pounds at 2800 rpm might be acceptable. I remember the old Chrysler V twin compressors back in the 70's use to run at a lot higher head pressures than other types at that time. From having worked on A/C and refrigeration systems for many years before I retired, when encountering sudden pressure changes it was generally caused by an issue with the valving or unloaders in the compressor. Have never seen a metering device cause a sudden change in pressure either. Even if one of the fans were to stop the change should be more gradual.
      Also could you have an issue with the dampers? Have you checked to make sure the hot water valve is off and there is no flow. Not sure where the water rad is located with respect to the evaporator but could be also an area to investigate.
       
    10. TechGuru

      TechGuru Well-Known Member

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      These use scroll compressors, no valving that I know of in them, they create a pulsed output.

      I may need to do the folded magazine test on the fan.

      It's perfectly cold when sitting parked at idle for even a hour. Then when I start going non-stop I can tell the compressor shuts off and the air starts to get a little warm then about a min later the compressor will come back on and it will be freezing cold.
       
    11. Donystoy

      Donystoy Active Member

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      Might be a tough one to diagnose. Not sure if these compressors are of the variable displacement type or not. If it is it will have an unloader valve assembly. Still is puzzling why it only happens while going non-stop. One would think that stop start traffic would create more overall heat.
       
    12. TechGuru

      TechGuru Well-Known Member

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      Scrolls are not variable displacement as far as I know.
       
      Last edited: June 13, 2018 at 12:24 PM
    13. Donystoy

      Donystoy Active Member

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      There are scroll compressors on some vehicles that do have variable displacement. In fact some do not even have a clutch so the compressor runs all the time and just bypasses when no cooling is required. Probably another attempt to cut weight and improve mileage. I am sure not crazy about that type as I like to be able to electrically switch off the compressor especially if it is starting to fail. I tried to do a Google search on our compressors to see if they were variable displacement but could not find any info. I do not believe that they are. Good luck solving your issue.

      My A/C has not worked for a couple of years. I have dry eyes and the cool air irritates me but I hope to get back to trying to get it operational again considering that it is suppose to be a long hot summer.
       
    14. TechGuru

      TechGuru Well-Known Member

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      Try putting your cool air on floor instead of the vents blowing it in your eyes...
       

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