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Thread: A/C not working

  1. Default A/C not working

    Hoping that the brain trust can find the hole in my logic, and save me from taking my dash apart.

    When I push the fan control to turn on the air conditioner, nothing happens. No light, no compressor, no change at all.

    I don’t think its fuse 11 or 12 because the interior fan works
    I don’t think it’s the ground because the interior fan works
    I don’t think it’s the thermostat, trinary switch or relay RR01 because the AC light does not come on.
    I fear it’s the switch itself, or the plug to the switch.

    The way I am reading the Heating ventilation air conditioning circuit, if fuse 11 and/or 12 is good and the ac switch is working, and the ground point is good, I should have a light at minimum.

    Hope there is something I am overlooking.
    Any Ideas?

    as Jeff said on removing the dash

    Quote Originally Posted by NobleM400 View Post
    All you need is 3 foot long, triple-jointed arms, eyes and lights embedded in your hands, and more patience than anybody I know. Jeff
    Future Reference. The HVAC dash control panel part # 95AB18C419BC HVAC Fan switch 6422008 from a Ford Escort Cosworth 1995-2001

    Search tags ac a/c air conditioner conditioning con
    Last edited by doug_porsche; 05-10-2016 at 03:49 PM.

  2. #2
    Join Date
    Feb 2014
    Rep Power


    Check for leaks in the system. If the pressure drops below certain level, the AC shuts down. At least that was my case.
    You can try refilling the system using an AC kit and see if it starts working.

  3. Default

    Thanks, but...

    If I am reading the schematic correctly (50/50 chance), high or low pressure would not trigger the trinary switch, which would not energize the relay (RR01) to turn on the compressor clutch.

    The light in the fan speed knob, which does not come on, is before the trinary switch.

    Summary: the Light in the fan speed knob should come on regardless of the system refrigerant charge.

  4. Default

    Well dang.
    I was trouble shooting.
    A/C light bulb in the switch is good
    Ground side of the A/C light to ground checks out.
    Then I dropped the little, long spring that goes behind the light bulb, into the heater control.

    Guess its time to go spring fishing.

  5. #5


    Not if this is helpful, but when my system was completely drained, my AC light would still come on. When the AC was low-charged, light would still work. I was testing my AC system with the honda drivetrain, so I was constantly pushing the AC on/off to verify signals/wiring.

    I'm willing to bet it's the bulb that is dead or the actual controls.

    good luck

  6. Default

    Driven, thanks for the reality check!!!

    As I was reading the schematic (US Build manual, Section 8, page 15), the lamp should come on regardless of the system pressure (measured by the trunary switch) and/or the thermostat (but having a second example is always good).

    According to my schematic power comes in via fuses 11 & 12, goes to the HVAC dash switch. I know this much of the circuit works as my heater fan works.
    The AC switch has an output, pin 6, that is tied to the input, pin 5, that goes though the lamp and then out, pin 31, to ground. I know my lamp socket to ground piece is good as I tested it today with the ohm meter. The Lamp also tested good via the ohm meter.

    Looks like I need to take the dash apart and test the actual HVAC switch.

  7. #7
    Join Date
    Jun 2015
    Charlotte, NC
    Rep Power


    Do fans come on in front when you turn A/C knob in and on? Those fans should always turn if A/c is on. If the freon level drops the a/c won't work and fans won't turn. Man I hope you don't have to tear things apart!

  8. Default

    They do not.

    Why I am not chasing the freon level yet is.

    If the the ac switch does not work (passing 12v to pin 6), the light will not come an & the ac will not be powered on.

    after I verify the by pushing the ac switch, 12v is going to pin 6, I will verify the pressures.

    Looks like my my dash is going to come apart.

  9. Default


    1) Seems to be its either a British car with random electrical issues
    2) The plug was slightly loose going into the dash switch (see 1).

  10. Default

    Update II

    AC works on the fresh air side of the switch, but not the re circulation side of the switch.

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