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no ac clutch in ac mode

Discussion in 'Technical Q&A' started by vonce45, Nov 23, 2013.

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  1. vonce45

    vonce45 Rookie

    Nov 23, 2013
    3
    #1 vonce45, Nov 23, 2013
    I am working on a 1990 testarossa and can not get the ac clutch to come in ac mode but it will come on in defrost like it is supposed to.I have replaced the blower res. and that is working but the temp. control in the console seem like it dosnt change anything the knob has no drag to it. Any ideas?
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,776
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Nov 23, 2013
    Do the "Sensor efficiency check" at the 6-pin connector of the AC ECU as described on pages H29-H30 in the TR WSM.

    PS You wrote "I have replaced the blower res. and..." -- did you mean that you replaced the blower Power Transistor?
     
  3. vonce45

    vonce45 Rookie

    Nov 23, 2013
    3
    #3 vonce45, Nov 24, 2013
    Yes Steve the power transistor.Thanks for the reply. I will check at the A/C ECU and will post what I find. Just so you know this car has been stored for 10 years and only has 7000 miles on it.....too much sitting I think. Have replaced the a/c compressor and drier and also flushed the system and recharged w/r134a pressures high and low are fine but no clutch or condenser fan in a/c. Have a/c clutch in defrost and condenser fan when pressure high side rises ill check that connector .
     
  4. vonce45

    vonce45 Rookie

    Nov 23, 2013
    3
    #4 vonce45, Nov 25, 2013
    Hello Steve I did the sensor check at the 6 pin connecter and both ohm out. The temp control knob ohms out 10.01 to 0.00. I removed all the white connecters from the fuse block and found no discoloring on the plugs. The only signal I am not getting is the one that trips the relay in the a/c control box. Checked the pressure switch on the new drier and it ohms out too. I gotta tell you this ones got me. Any more help ?
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,776
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Nov 29, 2013
    Not sure what you mean by "both" here. There are 5 resistance measurements to be made (while noting the ambient temperature):
    pin 1 to pin 2
    pin 1 to pin 3
    pin 1 to pin 4
    pin 1 to pin 5 (while turning the temp control knob)
    pin 1 to pin 6

    Can you post all the values?

    I realize that you probably just mistyped, but the resistance value should change from 0 to 10K Ohms (not 10 Ohms) between pin 1 and pin 5 when you turn the temp knob from full cold to full hot.

    Not a good sign for the AC ECU -- if all five resistance measurements are OK.

    Are you measuring for "the one that trips the relay in the a/c control box" at the CN (orange-black) wires connected to pin II of the 4-pin AC ECU or somewhere downstream? If downstream, then you bring some other connections into the picture.
     
  6. taneshaleo

    taneshaleo Rookie

    Dec 19, 2013
    5
    #6 taneshaleo, Jan 2, 2014
    If you have no voltage going to the clutch plug, check the A/C relay by plugging another relay known to be good.
     

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