1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

AC Not Cycling

Discussion in '80-Series Tech' started by AppleTech, Aug 12, 2017.

  1. AppleTech

    AppleTech

    Messages:
    838
    Likes Received:
    28
    Joined:
    Nov 11, 2007
    Location:
    Nashville, TN
    So my truck (1996) was low on R134a - it has a slow leak. Just started getting hot from a charge up about 2 -3 years ago so I have put off fixing it.

    I started refilling it today and was aiming for 28-35 PSI on the low side per the manual. I was on my way up to 35 around 32 PSI (I was stopping the fill to check intermittently) when all the sudden the AC compressor locked up and the belt spun around. During the fill process, it never clicked off once. I evacuated enough that the AC ran normally (feels good and no lockup) and at 1500RPM I'm seeing upper 20's for PSI on the low side. Not quite where it should be but its blowing cold so I'm not going to fuss with it.

    The question I have is shouldn't the compressor be cycling on and off? And shouldn't the overpressure switch be shutting the clutch off when it gets too full? I kept adding because the compressor never cycled. It is old and probably original so I'm considering that I may just need to replace it, but is that overpressure switch internal to the compressor? Also am I wrong in my thinking and approach to troubleshooting?
     
  2. Brandon98

    Brandon98

    Messages:
    123
    Likes Received:
    114
    Joined:
    Aug 2, 2014
    Location:
    The Savannah River Valley
    How much refrigerant did you put in? Any chance you slugged the compressor with a hit of liquid 134 instead of gaseous? In all likelyhood, the compressor's seen better days. Get a Denso from Rock Auto, new receiver dryer, and get to work. In addition, your evaporator is probably nasty and the TXV is tired. The evaporator only takes about 2 hours to get in and out. Go with Denso. Avoid Four Seasons. 7 oz of PAG-46 oil, as I recall.
     
  3. kruisinkid

    kruisinkid topless dorkel SILVER Star

    Messages:
    1,507
    Likes Received:
    179
    Joined:
    Jul 23, 2013
    Location:
    BK/PA
    pressure switch is all the way over by the battery and sight glass. without knowing weight of 134 you probably have to troubleshoot with the sightglass. adding an ounce of oil or 2 prob wouldnt hurt
     
  4. AppleTech

    AppleTech

    Messages:
    838
    Likes Received:
    28
    Joined:
    Nov 11, 2007
    Location:
    Nashville, TN
    How would one give it liquid R134? I just have the canisters you tap from the local auto parts store going into my gauge set's center line.
     
  5. SUMMIT CRUISERS

    SUMMIT CRUISERS SILVER Star

    Messages:
    1,791
    Likes Received:
    409
    Joined:
    Mar 25, 2005
    Location:
    Edmond, Oklahoma
    If you turned the can upside down you would get liquid.
     
  6. AppleTech

    AppleTech

    Messages:
    838
    Likes Received:
    28
    Joined:
    Nov 11, 2007
    Location:
    Nashville, TN
    Ahah so that may be it then - someone had told me to shake the can around and try and get everything out of it but it sounds like that is a bad idea! So really my low PSI reading is correct even though I've got icy AC? Should I try and add some more in without tipping the cans until I get to the correct PSI and then the compressor would actually cycle?
     
  7. SUMMIT CRUISERS

    SUMMIT CRUISERS SILVER Star

    Messages:
    1,791
    Likes Received:
    409
    Joined:
    Mar 25, 2005
    Location:
    Edmond, Oklahoma
    As far as shaking the cans, most cans I've seen have directions to twist between 12:00 and 3:00. If your AC is icy, sounds like you're good. How cold is it with a temp gauge in the vent? The vent temp needs to read somewhere between 34 and 40 before the compressor shuts off.
     
  8. flintknapper

    flintknapper

    Messages:
    3,583
    Likes Received:
    680
    Joined:
    May 22, 2004
    Location:
    Deep East Texas
    ^^^^^^^^ Expand above