A/C clutch problem ( i think ... )

Discussion in 'Technical' started by acme, Jun 5, 2019.

  1. acme

    acme Member

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    Hello
    I have a problem with the A/C system on my 70 Maverick.
    My A/C clutch won't engage when I put it on with the control panel. However, I have 12.4v ( mesured engine at idle )
    But, when I connect the clutch directly on the batterry ( 14v at idle ) it engage…..
    What do you think? What can be the problem?
    It is the stock clutch. Is it to old?

    Thanks for your hlep

    Stéphane from France
     
  2. 71gold

    71gold Frank Cooper Supporting Member

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    if it runs by jumping the switch,,,sounds like switch is bad or loose connection.
     
    Last edited: Jun 6, 2019
  3. Krazy Comet

    Krazy Comet Tom

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    Likely if clutch were problem, it would not engage with power from battery. BUT if you have 12.4v at clutch when fed from switch, it should engage. I'm assuming this is a late/modern compressor? Possibly the air gap between clutch and plate is too wide? That'd account for higher voltage operating clutch.

    IF everything to/from sw is OK, I'd connect a relay direct from battery for clutch power and operate the relay coil with the switch wiring. Sort of like adding a relay to headlight, horn circuit etc.
     
  4. acme

    acme Member

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    Thanks for your answers

    Yesterday, I connected the clutch directly to the battery whith engine off ( 12.4v mesured ) and Clic, the clutch engage….
    Engine off but ignition on, I mesured 10.6v on the wire from the control pannel.

    So, 12.4v with the battery, clutch engage .
    12.4v ( engine on ) with the wire from the control pannel, cluth don't engage….

    All the A/C système is stock from 1970..... Cluth, compressor, etc.…

    I'm a little bit confused….. ????????
     
  5. Krazy Comet

    Krazy Comet Tom

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    Was the 10.6v measured with clutch powered(connected) or disconnected?

    Due to size of wiring used, there will be voltage drop when a load such as compressor clutch is activated. The question, is approx 2v drop normal? I'd guess so. At least that's the case in headlight circuits & reason addition of relays are popular. The extra 2v gives brighter lights.

    Have you tried to engage clutch with engine running? In that case battery voltage should be around 14.4v, so 2 v drop in wiring would give a bit over 12v.
     
  6. acme

    acme Member

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    All the measure from the control panel wire were made with clutch disconnected. 10.6v with just ignition on and 12.4v with engine running.

    Yesterday, I tried to measure this wire voltage with the clutch connected.
    The voltage dropped to almost 0v ( engine running or not...same thing…)

    It means that something on the wire drain the voltage, right?
    An idea?
     
  7. Krazy Comet

    Krazy Comet Tom

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    Ahhhh now we have the whole story.

    If something were connected to wire dragged down the voltage to almost zero, it would have blown a fuse or smoked.

    What you have is a high resistance(poor) connection, probably in A/C switch. To troubleshoot, leave compressor connected and measure voltage at switch, probably will have voltage entering switch but not coming out. If it isn't switch, check the various connections in wiring to and from switch. The bulkhead connector is another possibility, though I believe power out of A/C switch feeds to A/C plenum and through firewall.

    BTW the relay I mentioned will not fix this issue, apparently there isn't enough current available to operate the relay coil.
     
  8. acme

    acme Member

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    Sorry for not having answer earlier

    Thanks for your help. Now I know where I have to look at...
    It would be a good thing to fix this problem before summer…..

    Thanks a lot
     
  9. Doug

    Doug Member

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    I have found when measuring power you show enough power but hook up a test light and it won't light . Also clutches need a lot of power to engage . You might need a relay to power your clutch . Just my 2 cents
     
  10. 71gold

    71gold Frank Cooper Supporting Member

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    have you gotten this straightened out yet...:huh:
     

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