strange A/C issue

Discussion in '80-Series Tech' started by Stecz, May 16, 2018.

  1. Stecz

    Stecz

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    This weekend, I drove my '97 LX (with 285k miles) about 1900 miles and noticed a strange issue with the A/C. On my normal commute (rush hour, stop and go, etc) , in the afternoon sun and 97 degrees, I keep the thermostat on the A/C above 65 degrees, otherwise, the A/C is uncomfortably cold.

    However, returning home this weekend, after driving for 7 hours or so at 75ish, the AC started to get uncomfortably warm, even though it was sunny and 83 degrees. The air coming out of the vents was definitely colder than ambient, but I had the AC on full cold max fan and it wasn't cooling that well. We stopped for a break for maybe 30 minutes and after the break, the AC cooled much better.

    Any thoughts on where to look? I guess I need to start with checking the A/C coolant pressure to make sure it's up to spec.

    thanks,

    John S
    97 LX450
     
  2. flintknapper

    flintknapper

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    TXV probably freezing up. When it thaws out the system will cool again, then when it freezes again....it won't.

    That is my first guess. Moisture in the system, most likely cause.

    Could be a number of other things as well. But yes, put a set of gauges on it and see what you have high and low side.
     
  3. Stecz

    Stecz

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    with water in the system, I assume it's an evacuate, replace dryer, add coolant back in type of operation?
     
  4. graham5david

    graham5david

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    80s have a AC compressor cut off switch that will shut off the compressor if the vehicle starts to slightly overheat .Sensor that activates the switch could be getting old . Or it may have got a little warm. However I would have expected it to get warm in the 97 degree heat not the 83. But it may be worth checking out especially since the temp guage on the 80 really doesn't move much even when it's overheating.
     
  5. graham5david

    graham5david

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    Were you traveling up a slight grade oulr pulling a load or pushing a strong headwind on the way home . That could be enough to get the temp to creep up enough to shut off the AC compressor.
     
  6. flintknapper

    flintknapper

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    Yes, IF that is your problem.

    As mentioned by others the A/C will cut out when coolant temps reach a certain level (about 226° F). So its possible you could be overheating OR that your coolant temperature sensor is faulty or a poor connection, resistance.
     
  7. secretasiansam

    secretasiansam

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    You can get a obd2 reader and see if high engine temps are cutting off the compressor. My guess is the expansion valve like flintknapper said. They are known to go bad/freeze up on high mileage 80s.
     
  8. ZackR

    ZackR

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    Sounds like an expansion valve issue or moisture in the system. I had a similar issue last year after repairing a broken AC line and recharging the system only to find out it would cool intermittently then warm back up. I installed a new expansion valve, cleaned the evaporator and vacuumed/refilled the system and it's nice and cold now.
     
  9. Stecz

    Stecz

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    overheating... could be... I was on pretty flat ground, temp gauge sat in it's usual spot (agreed that it's not real accurate, so I'll hook up my OBDII reader) but the a/c not working was a long term issue. It wasn't OFF, it was just not cooling as usual. After it sat at a late lunch, it worked well for another 400 miles, in warmer ambient temps, driving just as fast (80 max) and we had to actually turn it down at one point because we were uncomfortably cool....
     
  10. flintknapper

    flintknapper

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    If the system never actually 'cut off' and you still had cooler than ambient air from the vents...then we are looking for an issue that causes diminished performance and not temperature related shutdown.

    I would start by putting a set of gauges on it to check pressures (read refrigerant charge) and also look for restrictions. It's not a bad idea to check system pressure every few years even if it seems to be cooling O.K. most of the time. An undercharged system (Low on refrigerant) can cause the evaporator to freeze up (TXV too).

    Moisture in the system is another thing that can freeze at the TXV. Both of these conditions would manifest as the symptoms you are experiencing.

    Of course, there are other things that could be your trouble as well. (Faulty thermistor(s), blend door sticking, intermittent A/C amp)...the list goes on. I'd start with the basics and check the most 'likely' areas.
     
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  11. Stecz

    Stecz

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    Thanks for all of the suggestions, this gives me a direction to start on.
     
  12. lumbee1

    lumbee1 Native American

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    When driving out west (I'm from the east coast) I noticed our AC performed just OK until we hit a rainstorm. When the rain hit the condensor, the air conditioning got really cold and we either had to at least turn it down or turn it off completely.
     
  13. flintknapper

    flintknapper

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    ^^^^^ Normal for the system.
     
  14. Tools R Us

    Tools R Us

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    Yep, dry air makes cooling significantly more challenging.
     
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