AC Pressure Switch | FerrariChat

AC Pressure Switch

Discussion in '308/328' started by CL308GTB, Apr 26, 2019.

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  1. CL308GTB

    CL308GTB Rookie

    Jan 23, 2019
    25
    Full Name:
    C L
    Quick question for the 308 AC experts over here...

    When I turn on the AC on my car, the clutch of the AC compressor does not engage. I have checked the power going to the compressor clutch and realized that I have no power at all. I note however that the right motor fan (the one dedicated to the AC) goes on so it means that if there is something wrong, it is between the AC relay and the AC compressor.

    I also note that, between the AC relay and AC compressor, there are two pressure switches which roles are to stop the Compressor in case the pressure in the system is too low or too high.

    In my case, It's probably been more than two years since the last recharge of the system, so here are my questions:

    1. Is it possible that the pressure in the system (since the last charge) dropped so low that the low AC pressure switch prevent the compressor from turning on?

    2. Where is located this low AC pressure switch on the car? I have found the high AC pressure switch (#107213 or 16. on the exploded view: https://www.eurospares.co.uk/parts/ferrari/308-quattrovalvole-1985/cooling-heating/air-conditioning-system-38812) but can't find the low one​

    Before recharging the AC system, or investigating any leak in the system, as the case maybe, I would like to make sure that these switches are working properly.

    Thanks in advance
     
  2. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    1. Yes.
    2. The pressure switch on the dryer is the only one I'm familiar with. If you put a jumper wire on the connector, you'll hear the compressor clutch 'click' if the clutch is functional. If you hear the click, then system pressure is your next place to correct.
     
  3. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,753
    Shreveport, LA
    From my limited experience:

    1. Yes, and is likely. Have a jumper wire to bypass the switch to turn the compressor on.

    2. In my car, '88 328 there is only one switch that has a high and low2 pressure cutoff function.
     
  4. CL308GTB

    CL308GTB Rookie

    Jan 23, 2019
    25
    Full Name:
    C L
    Thank you both. This is very helpful.

    Next step now: I will bypass the switch as you suggest and check whether my compressor clutch is functional.
     
  5. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,753
    Shreveport, LA
    Find a 12v source. Battery is pretty far away but a good source, run a wire from the Pos side and briefly touch it to the compressor wire, you will hear a clank.
     
  6. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,753
    Shreveport, LA
  7. Martin308GTB

    Martin308GTB F1 Rookie

    Jan 22, 2003
    4,212
    Black Forest Germany
    Full Name:
    Martin N.
    When replacing the switch, check the threads. The original Ferrari switch had a thread M10x1. At least on the 308 applications. The widely available replacement switches have an 3/8"-24UNF-thread. They are close and one can screw the parts together, but I would not rely on a connection with an UNF-male into a metric female thread.
    I went through this recently and made an adaptor.

    Image Unavailable, Please Login

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    Best from Germany
    Martin
     
    CL308GTB likes this.
  8. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,753
    Shreveport, LA
    Hmm... VERY GOOD to know Martin! I can check my original easily enough.

    Thanks!

    Lester
     
  9. schelle_pelle

    schelle_pelle Karting

    Oct 22, 2021
    161
    Berlin, Germany
    Is there another cross reference available? Maybe from TGK?
     
  10. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
    1,109
    Mansfield, TX
    Full Name:
    Ron
    If you have the original AC hoses it has probably leaked. Especially, if using R-134a.
     
  11. schelle_pelle

    schelle_pelle Karting

    Oct 22, 2021
    161
    Berlin, Germany
    Thanks. I have no leak issue. I just want to acquire a pressure switch. ;-)
     
  12. Sergio Tavares

    Sergio Tavares Formula Junior

    Nov 15, 2018
    841
    Full Name:
    Sergio Tavares
    This is a normale binary pressure switch with standard threads $32 USD.
    https://www.napaonline.com/en/p/TEM207792
    You can use any but pressure choice must be correct one for chemical refrigerant you use. If you use R12 switch for R-134a then the pressure cutoff too early and R-134a misses optimal pressure because R-134a must operate higher pressure
     
  13. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    Before I messed with it I would check the A/C pressure. If its too low the compressor won't engage. I think the normal pressure with the engine off is 125 to 150 psi. If you change the pressure switch you will probably have to recharge it anyway. I changed mine to r134 a while ago but didn't realize it needed a different pressure switch. Guess that's next on my list.
     
  14. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    BTW my 78 GTS A/C is all original with the exception of the drier and O rings and with R134 it has held pressure for 2 years.
     
  15. Sergio Tavares

    Sergio Tavares Formula Junior

    Nov 15, 2018
    841
    Full Name:
    Sergio Tavares
    '

    Switch high pressure cutoff is only 1 bar difference so not super important as AC still runs OK, just not super optimum
     
  16. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    Yup. My AC works pretty well. One of my projects is to change the cabin fan to the higher capacity SPAL unit and since I will have to recharge it anyways I will change to the higher pressure switch.
     
  17. Sergio Tavares

    Sergio Tavares Formula Junior

    Nov 15, 2018
    841
    Full Name:
    Sergio Tavares
    yes only 15psi so a little longer time but is OK
     

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