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ac low pressure switch won't cycle - 98 explorer

Discussion in 'Stock 1995 - 2001 Explorers' started by ddeen, June 13, 2010.

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    1. ddeen

      ddeen New Member

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      Can somebody help point me to a thread that addresses subject concern if it has already been covered. Just recharged my ac system because clutch was not cycling. Charge levels look to be correct now but compressor clutch still does not engage. I jumped the low pressure switch and the clutch engages. I thought it was the switch so I replaced it with a new one but it did not fix the problem. Any ideas on what is wrong ? Thanks.
       
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    3. safn1949

      safn1949 Active Member

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      Check the AC pressure at the switch port and if it is good and the AC works correctly with the switch jumped you have a bad switch,just because it's new doesn't mean it's any good.

      When you jump it does the AC blow cold,are the pressures correct? Post your high and low side pressures sitting and running.:D
       
    4. ddeen

      ddeen New Member

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      safn1949, thanks. Just checked the low side port and pressure = 39 PSI and does not change if engine is running with AC on. Jumped the low side switch again and the air blowing inside is not cold. Now I am completely stumped. I don't have a tool to measure high side pressure.
       
    5. ranger7ltr

      ranger7ltr Elite Explorer

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      39 psi static pressure is not enough...

      Are you measuring system pressure with the compressor off? If so, that is static pressure...When you jumpered the low pressure switch, did the compressor actually engage? If it did engage, there is not enough refrigerant in the system to start the cooling process...

      Even with whatever gauge you are using, if the compressor kicks in, what is the pressure reading at that point? To actually start the cooling process [and close the low pressure switch]the system would need approx. 70-100 psi static pressure...And you really need to monitor the high side pressures to know the charge level before the pressures go too high and get to the level of blowing stuff up...Since jumpering the low pressure switch engaged the clutch, the electrical system for the a/c is working and you just need to get the system pressure high enough to close the switch...

      Your high side should be 2.2-2.7x ambient temp and anything higher than that tells you the cooling of the condensor is not sufficient or there is a problem inside the system...
       
    6. safn1949

      safn1949 Active Member

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      Yep,sounds like a low charge.I spent all my years with R-12 but running with the AC on and cold the low side should be around 35 psi with 134A I think.But I know someone who fools with 134 will correct me if I'm wrong.:D
       
    7. ddeen

      ddeen New Member

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      Thanks. I have borrowed and better guage from work. I can now check low pressure and high pressure side. I will also check static v.s dynamic pressure. Will know more tonight.
       
    8. ranger7ltr

      ranger7ltr Elite Explorer

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      Static pressures are the same...Running or dynamic pressures will vary...

      Since R-134A runs at higher pressures what you can expect is for the high side pressures to follow the 2.2-2.7x ambient temp guideline...The low side pressures still reflect the approx. evaporator temps...

      One other difference is that an R-134a system charge is more critical to being under or over charged...Where you could "top off" an R-12 charge and be close to correct, R-134a is best charged into a vacuum by weight and then not adjusted...Of course people do this and they will usually find the cooling is ok but not as cold as they would like...It does take more finesse to top off a R-134a system and not over charge it...
       
    9. ddeen

      ddeen New Member

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      Thank you all for all the good advice. The guages I borrowed from work were used and abused and leaked. I had to go to plan B. I could only measure the low pressure side. I filled it up to as much as my one can could fill. It measured to about 65PSI static and 15 PSI dynamic. The compressor now engages intermitently. At this point I really think it is just undercharged. I am satisfied with what I have done and learned and will take it to a AC shop and get it evap/filled properly.
       
    10. safn1949

      safn1949 Active Member

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      Yep,way too low on the low side.I have a slow leak in my 94 so I just top it off every year,but I also live in Minnesota so it's not as critical.I might use it 6 times a year.For example it's June 14th and 66 F outside.:D
       
    11. ddeen

      ddeen New Member

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      quick update. I bought a 19oz can and got it to fully load. low pressure is running at around 34PSI. Fixed the problem. System is running good. Thought I would post an update to help folks that are going through the same problem. Saved a couple $ trouble shooting this myself.
       
    12. Drew_Rymer

      Drew_Rymer New Member

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      98 Explorer AC is Not Blowing out Cold air Please Help

      I'm having a similar problem with my AC for my 98 Explorer. The AC is working just not blowing out cold air and when I set the AC on Max AC and then accelerate it stops blowing air out of the vents and starts blowing air up out of the defroster vents...I Don't know why maybe the AC Clutch??

      I purchased one of those shitty recharge kits w/ a gauge and when I attach it to my Low Pressure Port the PSI goes from the green (not sure what PSI exactly I think about 20 - 30 PSI) to over 100 - 120 PSI (The Red) then the compressor engages and it goes back down to about 20 - 30 PSI (the Green on the gauge) and it just keeps idling back and forth while the engine is running. So how the hell do I know if I can recharge the system w/o possibly damaging one of the hoses and sending myself up shit creek w/o a paddle? I live in Sacramento CA and luckily it's not hot for now but it will get back up to the 90's and 100's soon. Any tips or suggestions would be much appreciated. Thanks :roll:
       

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