A/C Clutch will not engage, but air will blow.

Discussion in 'Fox 5.0 Mustang Tech' started by Dbeck002, Dec 25, 2006.


  1. Dbeck002

    Dbeck002 New Member

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    Not too long ago i had my A/C fixed, it was working fine. Just the other day i turned it on and the fans inside the car would blow but the A/C clutch to the compressor would not engage. I probed the connector going to the A/C clutch and it shows around 8 volts when the car is on. Is there a fuse that may have blown? My AC compressor pulley (the actual pulley, not just the idler) turns easily by hand but the magnetic clutch will not engage when i turn it on.

    Please help,

    Thanks.
    #1
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    If the compressor won’t run with the A/C switch in the A/C on position, then the system is
    likely to be low on refrigerant. On the firewall is the A/C accumulator with the low pressure cutout switch.
    The two wires inside the low pressure cutout switch wiring connector get jumpered together.
    That bypasses the switch and turns on the compressor when the refrigerant level is low.
    Don't run the system very long, because low refrigerant also means low oil. The refrigerant
    causes the oil to circulate though the system and lubricate the compressor.

    Diagram courtesy of Tmoss & Stang&2birds
    [​IMG]

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagra
    #2
  3. Dbeck002

    Dbeck002 New Member

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    Thanks Jrichker, helpful as always.

    Im going to jump the two terminals on the canister and see if that helps.

    BRB.
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  4. Dbeck002

    Dbeck002 New Member

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    I just did the test and i heard the AC clutch click on. Looks like my system was low, i guess there is a leak somewhere.

    At least it wont be as costly to fix now that i know its just refiregerant, thanks again.
    #4
  5. glowstang93

    glowstang93 Member

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    Joe, I jumped my low pressure switch and clutch is still not engaging. I checked the voltage from wire to wire at the compressor plug and I got 6 volts. What should the reading be at that point?

    I have the electrical type clutch, not the stock one, been in car for 7 years, if this makes a difference in diagnosing.
    #5
  6. BYRDPE

    BYRDPE Founding Member

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    just checking to make sure you had the system turned on during the test. i know i didn't the first time i tried it. :)
    #6
  7. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Air conditioning electrical troubleshooting 87-93 Mustangs.

    Diagrams courtesy of Tmoss & Stang&2birds
    [​IMG]

    Check out TMoss's diagram I posted. Anytime the clutch is energized, the black/yellow clutch power wire should show 12 volts or whatever the battery voltage is measured at the battery.

    Make sure the black ground wire is good, and that it connects to a clean bare metal place on the engine. Measure the voltage between the black/yellow wire and the battery ground cable. Good 12 volts, then you have a bad ground. The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges

    No 12 volts on the black/yellow wire, check voltage at the pink/blue wire on the WOT relay: it should be 12 volts. The WOT relay is located under the Mass air meter on the passenger side.

    Good 12 volts on the pink/blue wire on the WOT relay, ground the orange/lt blue wire on the WOT relay. Recheck for 12 volts on black/yellow wire. No 12 volts on the black/yellow wire, recheck your ground for the orange/lt blue wire. If it is good, replace the WOT relay.

    No 12 volts on the pink/blue wire on the WOT relay, check out the low pressure cutout switch. Look for 12 volts on the green/purple wire.

    No 12 volts on the green/purple wire, the A/C control switch is bad or the power to the switch is bad.


    The next step is valid only if you are sure there is sufficient refrigerant change to make the system operate. The low pressure switch is supposed to shut off the compressor if the refrigerant charge is low. It does this to protect the compressor, since the refrigerant helps to circulate the oil that lubricates the compressor.

    If there is good 12 volts at the green/purple wire, measure the voltage drop across the low pressure cutout switch. With the switch connected, probe the back of the switch connector. Use a pair of paper clips or safety pins to measure the voltage between the green/purple wire & pink/blue wire. Do not connect the voltmeter to ground, just the two wires. This measures the voltage drop across the low pressure cutout switch. You should see less than .75 volts. Less voltage drop is always good, but more voltage drop is bad. More than .75 volts, replace the low pressure cutout switch. It unscrews without draining the system or causing more than a short PIFF of gas escaping. The local auto parts store should have a replacement switch. Inspect the low pressure cutout switch wiring harness contacts before replacing the switch. A replacement pigtail is also available at the local auto parts store.



    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
    (website host) for help on 86-95 5.0 Mustang wiring Mustang FAQ - Engine Information Everyone should bookmark this site.


    Ignition switch wiring
    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    Fuel, alternator, A/C and ignition wiring
    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    Complete computer, actuator & sensor wiring diagram for 88-91 5.0 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Complete computer, actuator & sensor wiring diagram for 91-93 5.0 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

    Complete computer, actuator & sensor wiring diagram for 94-95 5.0 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

    Vacuum diagram 89-93 Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

    HVAC vacuum diagram
    http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

    TFI module differences & pinout
    http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

    Fuse box layout
    http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif
    #7
  8. glowstang93

    glowstang93 Member

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    Thanks Joe, I think that answers my question that 6 volts is not good at the compressor plug. Any change you have a pic of the WOT relay? I'll probably just follow the wires back from the plug, should lead me to there. Will do some more investigating tomorrow.
    #8
  9. BYRDPE

    BYRDPE Founding Member

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    it's ~ 8-10" below the stock MAF.
    #9
  10. glowstang93

    glowstang93 Member

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    I really need some help finding the WOT. I went out and looked at it today. I started her up and the a/c blew cold with compressor clutch working. Then when I revved her up, it stopped working. Can notice some roughness to the engine, but not too bad. Remember its a 2.3, so it may be in a diff location, but if i knew what it looked like it would help... Any clue who would have one, any parts store? under what name?

    Thanks
    #10
  11. glowstang93

    glowstang93 Member

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    I think i found it, the ircm, integrated relay control module. Can you check it to make sure its bad or what? Guess it being a 93 is not as easy to fix
    #11
  12. glowstang93

    glowstang93 Member

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