A/C no workee

Discussion in '1994 - 1995 Specific Tech' started by Blackened302, Sep 27, 2005.


  1. Blackened302

    Blackened302 New Member

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    when i got the car, the a/c wasn't working--turns out all it needed was a new pressure switch. i replaced it about a month ago and it started working fine, even did a coolant recharge. a/c stopped working a couple days ago, though--all it does is blow hot air.

    question is how do i jump the pressure switch to test it and see if it's gone bad? there arn't any leaks--checked the hoses w/ the guage the coolant recharge kit comes with. i'm hoping it's just the switch, but why would it go bad so soon? any suggestions welcome, thanks guys.
  2. mo_dingo

    mo_dingo Well-Known Member

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    Just remove the pressure switch connector and jump the 2 terminals. The a/c should kick on. If it blows cold, your switch is bad. If it still blows hot, you are out of refridgerant.

    But the safe way is to check the pressure at the low side port with a gauge (az stocks them), which runs along the drivers side of the upper intake and the port is kinda under the STB, so you will need to remove it for better access.

    Scott
  3. Blackened302

    Blackened302 New Member

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    jumped the switch and no dice--seems like the switch is still good. as i mentioned, i refilled the coolant when i changed the switch, so only thing i can think of is i have a leak, even though the gauge reads there's pressure. suggestions?
  4. 94_Teal_GT

    94_Teal_GT Founding Member

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    Depends on which pressure switch he's referring to. The high side switch(near air filter) has 4 wires. That one has a red, black, green/orange, and a blue/yellow wire. I don't recommend shorting the wires together.

    Just check the pins IN the switch for resistance using a ohmmeter with the KEY OFF. Take note of which wires were where before you unplug it. The pins where the blue/yel and grn/org should show no resistance between them. These are the wires that control the low speed fan and the compressor. I believe the other 2(red one and black one) control the high speed fan.

    It's possible that whichever switch you didn't replace has now crapped out:shrug: The low pressure switch is mounted on the top of the accumulator? near the firewall on the passenger side. I think the wires are purple and blue. The switch should also show no resistance(if system has refrigerant in it) with KEY OFF. If the low pressure switch doesn't read 'shorted' then it's bad. Your A/C pressure gauge should read well over 100psi on the low side if the compressor is OFF. The low side switch 'opens' if the psi is below 25psi.
  5. Blackened302

    Blackened302 New Member

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    perhaps you're right, 94_Teal, the only switched i replaced was the low pressure switch that's mounted on top of the accumulator near the firewall on the passenger side--the wires are purple and blue.

    could you better explain the location of the other switch? the high side switch w/ 4 wires, please? thanks.
  6. 94_Teal_GT

    94_Teal_GT Founding Member

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    Sure thing, it's the switch that is nearly touching the very front right of the housing for your air cleaner, right behind the core support, near the radiator on passenger side, screwed right into a hard A/C line. The factory switch is goldish metal and a teal plastic color.

    Inspect the wires while you are there, the insulation fell off mine, so I had to replace some sections of the wires.
  7. Blackened302

    Blackened302 New Member

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    ah, i see which you're talking about. i'll check it out tomorrow and get back to you. thanks a lot for the responses.
  8. Blackened302

    Blackened302 New Member

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    checked the other switch today and it looked fine. i just replaced the low-pressure switch (one one top of comp--blue/purple wired one) and still nothing. a buddy's bringing his coolant guage again so we can double check that. i also checked all the fuses and no dice.
  9. mo_dingo

    mo_dingo Well-Known Member

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    Ok, so you jumped both the high and low pressure connectors and the a/c clutch did not engage?

    If so, do this. Take a multimeter and see if you have 12V at one of the terminals at the pressure sensor. If you don't, that means the sensor is not being told to activate, thus your a/c switch inside the car iis bad or some wiring inbetween.
    Scott
  10. 94_Teal_GT

    94_Teal_GT Founding Member

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    Does the low speed fan come on, when you switch on the A/C? It should start even if the motor is cold.

    While I don't condone this, I did it because I was told the system was fried(by a Ford Dealer) and didn't think there was much to lose. I jumped the blue/yellow to the green/orange at the high pressure switch with engine running and A/C switched on. This made the low speed fan come on, then about 5-10 seconds later the compressor switched on. But when I pulled the jumper, and plugged the harness back in, nothing. Don't mix the wires up and don't mess with the red and black wires.

    When I probed the switch on mine, everything checked out too, but it still didn't work. I ended up using my Dremel and a wire brush to clean the prongs inside the switch, after that the fan and compressor started working again, for now.
  11. Blackened302

    Blackened302 New Member

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    luckily the clutch did engage when we jumped it. we just didn't have the guage on us to check the level of coolant in the system. my buddy thinks it's not engaging 'cause it's low on coolant, so we're checking the level tomorrow w/ the guage and hopefully it's just that it needs a recharge. i also replaced the low pressure switch, i think i may have shorted it out trying to jump it. i'll try and get a hold of a multimeter to check for the 12v at the switch terminals. i should check the voltage at both the low and high switches, correct? if it turns out to be the interior a/c switches, will one off another stang work? direct swap, yes?

    the low speed fan does come on and the a/c compressor does turn, only the air doesn't blow cool inside. i checked teh terminals for any corrosion and such, and cleaned them out a bit with electrical contact cleaner i had left over from when i cleaned my MAF.

    as i said, i hope that it just nees a refill. i really appreciate the help, guys, thanks. i need my a/c... the car turned into my daily driver and it sucks riding around in 100+ degree weather.
  12. Blackened302

    Blackened302 New Member

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    why the hell do they call them "O-rings"? isn't a ring an O? that **** makes no sense... is there, like, an R-ring? anyhow, both o-rings were missing on the high and low pressure valves. you could see where both valves were leaking, so i'm gonna have to replace those. the compressor wasn't spinning cause there was little to no pressure, so a coolant refill did it. even though it'll leak and only last a few weeks, that gives me enough time to get the replacement valves. thanks for the help, guys, i really appreciate it.
  13. 94_Teal_GT

    94_Teal_GT Founding Member

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    Glad to hear you've tracked down the problem. :banana:
  14. Blackened302

    Blackened302 New Member

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    damnet, i hate having to ressurect this thread 'cause it means i'm still having problems w/ the a/c. i just refilled the coolant with yet another can 'cause i didn't have enough with the one last time. i imagine it's gonna work for a while, maybe, then crap out on me again, so here's what i'm thinking of doing: wiring a switch to the power wire of the compressor.

    do you guys think this is ok? safe? should i run a fuse, too? if so, how many amps--20? any suggestions/ideas on the power source i should use?

    again, i hate having to bug you all about this same old crap, but man, i need my a/c!!! thanks, guys.
  15. BlownFiveLiter

    BlownFiveLiter have car, will race....wait, it doesn't run

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    I wouldn't recommend it, speaking from experience (running jumper wires to the compressor with a switch). I had a fun experience on New Year's day where my car actually caught on fire because of a bad low pressure switch allowing my compressor to run, while the system was empty. Mine was hopefully an isolated incident where the switch actually worked, just not as intended. That being said, bypassing the safeguards in the system to allow it to run can be catastrophic. Once it goes empty, it gets very hot, very quickly. To me it sounds as though you've still got a leak somewhere, so I'd start looking in that direction.
  16. 94_Teal_GT

    94_Teal_GT Founding Member

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    :stupid:

    I agree with StangGT1995, running a jumper is an ok way to eliminate a sensor/switch as a problem, it's a bad idea to leave it that way.:nonono:

    Did you get the refrigerant with leak stopper/leak detector in it? If so, get a black light and shine it around the system at night. The dye shows up under ultra violet light. Check the low pressure valve, it seems mine may be leaking. I heard a quick pressure release, when I pulled the plastic cap off my low pressure side. I also found dye around the line going into the accumulator.
  17. Blackened302

    Blackened302 New Member

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    alright, looks like the idea for the switch is a strong no-no, heh. both bottles of coolant i used had the sealant and the detector in them, so i'll try and get a blacklight asap. thanks for the suggestions.
  18. mo_dingo

    mo_dingo Well-Known Member

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    yup, you are right on track......let us know.
    Scott
  19. Blackened302

    Blackened302 New Member

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    resurection!!! hehe, you can definately tell it's summer w/ all these A/C threads.

    NEW QUESTION: how do you jump the high-pressure switch!? this is the only part of the system i have yet to check. i see 4 wires...which goes to which?

    the low-pressure switch was simple because it was just 2 wries.

    when i started the car w/ a/c on max, i read 0 pressure. after about half a bottle of coolant, it read over 100 psi. why? thanks, guys.
  20. Synned

    Synned took tubgirl on a date and got banned

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