AF: A/C compressor not cycling off (but only on max/recirc setting) | Allpar Forums
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A/C compressor not cycling off (but only on max/recirc setting)

Discussion in 'EEK! - Every Extended-K Car' started by twankowski, Apr 28, 2020.

  1. twankowski

    twankowski Active Member

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    Just finished a ton of work on my boy's '89 Sundance 2.5NA. Along the way, noticed a visible leak (light oil plus dye) where the suction line meets the compressor. Anyway, re-sealed and vacuum tested the system, then evacuated, then added 30.5 ounces of R-134a, as I've done lots of times in the past.

    Pressures are good (45 and 200 low/high) on this cool-ish 70-degree day; dash outlet temps are steady at 45-46 degrees F. So here's the kicker...

    While I'm getting nice long cycle times on the compressor (roughly 45-50 seconds on, 10 seconds off) in normal mode, if I put the system on recirculate the compressor does not turn off.

    I watched it run for 10 minutes straight, which was enough time for a light coat of ice to form on all metal parts of the suction line, all the way to the expansion valve.

    If I pull the harness for the low-pressure cutoff, it naturally cuts off.

    Bottom line is this: "normal" A/C is great, "recirc" mode keeps the compressor on all the time to the point of ice forming on the suction line.

    Never seen this one before. Any ideas? Thanks!
     
  2. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    IMO, you overcharged the system. R134a conversion is supposed to be 80-85% of the amount of the original R12 fill. You're over that amount, and 200 psi is high for a 70F day. 45 psi is also too high with compressor engaged.

    If it's icing up, it's possible that the thermocouple embedded in the evaporator has failed. Its job is to cycle the compressor off several degrees above freezing temperature.
     
  3. AllanC

    AllanC Well-Known Member

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    If the suction pressure is 45 psi, that equates to refrigerant temperature of 49 degrees. So I would not suspect icing of the evaporator to occur.

    Try this test. Let the engine idle and run the A C with outside air ( no recirculation) and determine the suction and discharge pressure when the compressor cycles off and then when it cycles on again.

    Repeat the same test but with the recirculation enabled and watch the suction and discharge pressure over a period of a few minutes. If the system does not cycle the suction pressure should keep decreasing to below 20 psi possibly. Report your findings.
     
  4. ImperialCrown

    ImperialCrown Moderator
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    The compressor should still cycle as needed in Recirc.
    Selecting Recirc will close the fresh air door, so that only interior air is drawn in.
    A water valve in the heater hose should close off the heater core coolant circulation completely.
    If the line from the evaporator back to the suction side of the compressor is icing, then the evaporator may also be icing up and blocking cooled air flow.
     
  5. twankowski

    twankowski Active Member

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    Thanks all. Will re-check all and report back. Got very caught up in my normal job the last few days, so should get to it soon.

    Don't think it's overfilled. Factory R-12 fills on all of my cars (Daytona, Reliant and Sundance) is 38oz. I have carefully measured out 30.5oz for every R134 conversion and has served me well thus far.

    I'll hook up the gauges and post as soon as I can.
     
  6. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Interesting. All of my Daytonas had 32 oz factory fill.
     
  7. AllanC

    AllanC Well-Known Member

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    I checked a reference I found a number of years ago published by Four Seasons, supplier of A C components for the automotive trade. Up through year 1990, the Shadow / Sundance twins used 38 oz of R12 refrigerant. 1991 - 93 models used 32 oz of R12 refrigerant. I think the difference was that in 1991 Chrysler started changing equipment installed on vehicles from C171 compressor to the Nippondenso compressor and parallel flow condensers from serial flow condensers. This was in anticipation of adoption of R134a refrigerant. In the process the mass requirement of refrigerant was decreased.

    This is the reference link.

    https://www.4s.com/media/5421/four-seasons-capacity-guide.pdf
     
    #7 AllanC, May 1, 2020
    Last edited: May 1, 2020
    Bob Lincoln likes this.

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