AC help

Discussion in 'Import Vehicles' started by JThompson, Jun 25, 2017.

  1. JThompson

    JThompson Newbie

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    2004 Chevrolet trailblazer LS
    4.2 engine

    I replaced fan clutch and the only way to make the ac work is to jump the relay and it cools fine. I also bypassed the low pressure switch and did nothing. What am I missing
     
  2. kev2

    kev2 wrench

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    STOP jumping switches! It may not be the low pressure switch*, and computers do not like elec shorts.

    Scan for codes - yes even if CEL/SES is off. Some codes will have PCM restrict AC operation.

    Do you have gauges low and high pressure? The 'transducer'* will need to see a minimum/max static refrigerant pressure to permit AC operation.

    I suggest you check for codes first.

    let us know manual HVAC or AUTOMATIC HVAC....
     
  3. billr

    billr wrench Staff Member

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    Did the A/C work OK just before the fan clutch replacement? To me, a "fan clutch" is a viscous drive between the water pump and radiator fan; a purely mechanical device. Is that what you are referring to?
     
  4. JThompson

    JThompson Newbie

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    NO it did not but the fan was spinning very slowly and I was told it had a speed sensor that may have something to do with compressor kicking on.

    LIke I said if I jump the relay it blows really cold.
     
  5. JThompson

    JThompson Newbie

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    THe codes said to replace fan clutch.

    I did discover hot air blowing out of the passenger side vents

    45 low pressure and 200 high pressure and that show right base on ambient temp
     
  6. kev2

    kev2 wrench

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    OK we will help get it fixed let us know the code P0xxx?

    FYI or TMI-
    Jumping the relay removes all sensors and modules from system operation, an easy test but not much more. Yes there is a Hall effect 'sensor' reading fan speed which is controlled by the PCM.
    If the fan speed is lower than the PCM requests a fan code would set and PCM would restrict AC - logic would be - there is a cooling problem so why add to workload...
    The code is the first step here.

    A money saving tip - there is NO code that says replace a part.
     
    Last edited: Jun 25, 2017
  7. JThompson

    JThompson Newbie

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    I will get the code number and get back to you

    THanks so much for helping
     
  8. kev2

    kev2 wrench

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    have you tried a different relay? swap a like relay for testing....
     
  9. JThompson

    JThompson Newbie

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    I switched the relays and that did not make any difference
     
  10. JThompson

    JThompson Newbie

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    I switched relays and it did not make any difference
     
  11. kev2

    kev2 wrench

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    THen we are back to codes post ALL codes.


    Other ideas
    Do you have a scanner - live data, bi directional capabilities?
    Any recent work modifications or added devices?
     

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