A/C Compressor not cycling off

Discussion in 'Fox 5.0 Mustang Tech' started by FullOutPwr, Aug 18, 2011.


  1. FullOutPwr

    FullOutPwr Founding Member

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    A/c blows cold, but the compressor clutch will not cycle off. I've searched and some have mentioned a cycling pressure switch and maybe it needs to be adjusted, but I can't find instructions or other info on how to. Any ideas?

    I only have a low side gauge at the moment, but it's showing 38 psi dynamic pressure and obviously as the clutch will engage, its not low on pressure and the low side switch is working. High side issue or?
     
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  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    The pre 94 Mustangs had no compressor shutoff that was linked to a thermostat. The cold air temp was adjusted by the center mixing knob and the vent shutoff butterflies.

    There is a low pressure cutoff switch which will turn of the A/C compressor when the refrigerant level gets below the safe operating point. That keeps the compressor form being damaged for lack of circulating oil. The oil in an A/C system circulates with the refrigerant, and low refrigerant means low oil supply.
     
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  3. FullOutPwr

    FullOutPwr Founding Member

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    Well, currently no issues with getting the compressor on. The clutch will engage when I turn on the a/c and will get cold, however the compressor will not cycle on/off as is usual but is on 100% of the time until i turn the a/c off via the knob inside the vehicle if that makes sense.

    So i guess the question becomes what makes the a/c compressor cycle on/off to regulate temperature etc and to ensure none of the a/c lines freeze? Compressor constantly on to get cold a/c cant be good for the compressor or for my gas mileage with a constant load
     
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  4. drexelsteve

    drexelsteve Member

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    Sounds normal to me
     
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    The A/C suction line will frost over on the outside depending on the temp and outside humidity: that's normal. There isn't supposed to be any moisture inside the A/C lines because that makes acid that destroys the A/C system. That's one reason the A/C system gets vacuumed down when it is opened up and all the refrigerant is drained out. The vacuum removes the air and moisture that can damage the A/C system.

    The A/C compressor is designed to run constantly when the A/C or defrost is turned on. Yes, it does cause drag when it is running and that reduces gas mileage a little.
     
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  6. FullOutPwr

    FullOutPwr Founding Member

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  7. JungleJoe

    JungleJoe Member

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    Never heard of this. . . .Damn!
     
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