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  1. #1
    FEP Power Member fgross2006's Avatar
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    Default 84 LX 5.0 intermittent AC issues

    So i replaced the accumulator, the compressor with brand new not rebuilt one, new lines, LP switch and orifice tube around 4 summers ago. Worked fine every year till this one.

    First issue my mechanic found the refrigerant leaked out of the high pressure fitting so we replaced with new high and low pressure fittings, vacuumed and charged the system. After that I have been having issues where it will run ice cold for an hour or so then it will blow hot air. Sometimes after awhile cool, not cold air will trickle out. The problem is made worse by shutting off and restarting the car. Sometimes it will be working fine but after I shutoff the car and restart again it starts blowing hot air.

    At first my mechanic said he thought the low pressure switch was the issue so I swapped it twice, no change.

    The system is charged and not losing refrigerant. The other day I stopped by my mechanic when it was blowing cool, not cold and he checked voltage at the compressor plug and it was 10 volts. he says its too low. Should be no less than 12. So now I'm wondering if theres a relay between the low pressure switch and the compressor? I've read theres a WOT cutoff that cuts power the the compressor at WOT. I cant find it if an 84 has one. Could that be the issue and whee can I find it? Whats it look like?

  2. #2
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    You could try disconnecting the plug to the compressor and putting 12v directly from the battery to see if the clutch engages. That should give you cold air. Compare clutch action with 12v versus clutch action with the 10v of the plug hooked up.

    If the clutch engages fully with the plug connected, you might have a problem with the a/c / heater housing under the dash not routing air correctly.

  3. #3
    FEP Senior Member liv2roc's Avatar
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    The WOT switch is on the carb throttle linkage at the carb think it has 3 wires on it.

  4. #4
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by liv2roc View Post
    The WOT switch is on the carb throttle linkage at the carb think it has 3 wires on it.
    I have CFI, not a carb

  5. #5
    FEP Senior Member gt4494's Avatar
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    As long as the clutch is staying engaged and not slipping the voltage it should not be causing the problem. just make sure the center of the clutch (electro magnet) and the pulley (compressor drive) are both turning the same at all rpm.

    have you checked the vacuum controlled heater doors? if the door sticks open or partway you will get the ac and the heat coming out the same ducts. the heater always has hot water running through the core.
    "If you can't explain it simply, you don't understand it well enough."
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  6. #6
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by gt4494 View Post
    As long as the clutch is staying engaged and not slipping the voltage it should not be causing the problem. just make sure the center of the clutch (electro magnet) and the pulley (compressor drive) are both turning the same at all rpm.

    have you checked the vacuum controlled heater doors? if the door sticks open or partway you will get the ac and the heat coming out the same ducts. the heater always has hot water running through the core.
    Thats not an issue. When it fails I pop the hood and find the clutch not engaged. Its electrical im certain of it

  7. #7
    FEP Senior Member Tigger's Avatar
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    Maybe something is wrong with your clutch and the electromagnet? Mine would disengage half way home from work then the air would get hot. I’d have to stop and whack it with a 2x4 but that would only last a couple miles and then it would disengage again. It would work fine for the first 10-15 miles then it would cut out. I replaced my ac clutch and gave no more problems.
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  8. #8
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by Tigger View Post
    Maybe something is wrong with your clutch and the electromagnet? Mine would disengage half way home from work then the air would get hot. I’d have to stop and whack it with a 2x4 but that would only last a couple miles and then it would disengage again. It would work fine for the first 10-15 miles then it would cut out. I replaced my ac clutch and gave no more problems.
    I'd be very surprised since this was a brand new, not rebuilt compressor I put in just 3 summers ago. I still have my original since there was no core charge on it. Is the clutch even a replaceable part on this compressor?

  9. #9
    FEP Power Member fgross2006's Avatar
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    what I really want to check is there an AC relay on the 84 5.0? I cant find it and cant find a part number for it either. My research shows that on later model Mustangs, 86 - up, there's a relay between the low pressure switch and the AC clutch connector and its a failure point.

  10. #10
    FEP Power Member fgross2006's Avatar
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    I guess I'll answer my own question. the AC relay is behind the passenger strut tower. If not visible through wires and loom just nudge the loom to the side. I found it by tracing the wires from the LP cutoff switch. As I got near the relay just jiggling the wires made the clutch kick on, so I knew this was the source of my intermittent loss of power to the AC clutch. I picked up a Standard relay and swapped it out. So far its running consistently and running cold, not just cool. I rechecked voltage to the clutch connector and now its running at 11.4 volts. Last week it was at 10.4. I hope one volt extra makes the difference. Time will tell.

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    Also when tracing the AC wiring near the LP cutoff switch I found the wires also run though a Duraspark connector. The female end has dry rotted wire casing and exposed wires. i recall finding this when i was doing my motor swap 3 summers ago and at the time I was more concerned with getting my motor dropped in and reassembled so i tapped it up and intended to get back to it at a later time. Totally forgot about it till today. Luckily LMR has a Duraspark repair female connector for 16 bucks. I ordered it and will swap it out. Hopefully that will clean up the wiring problems.

    https://lmr.com/item/HDW-14289/83-85...repair-pigtail

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    Last edited by fgross2006; 07-31-2019 at 08:15 PM.

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