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Isobaric valve

Discussion in 'Maserati' started by thecarnut, Jan 16, 2020.

  1. thecarnut

    thecarnut Formula 3

    Apr 22, 2006
    2,328
    Atlanta
    Full Name:
    The Car Nut
    York A/C compressors on most Maseratis were fitted with an isobaric valve that somehow was designed to protect the system if the pressure got too high. Does anyone know how to bench test these valves? At what pressure does the electric switch close?

    Ivan

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  2. 71Satisfaction

    71Satisfaction Formula Junior

    Jul 15, 2012
    709
    New York and Norway
    Full Name:
    Art
    Were the York components shared with Citroen-era Maseratis? If so, look up Dave Burnham and give his shop a call...?
    - Art
     
  3. boralogist

    boralogist Formula Junior

    Jun 21, 2005
    461
    According to Maserati the isobaric valve works almost like an invertor NOT a binary switch---except in cases of a fatal gas leak:

    The Isobaric valve replaces the pressure regulator, fitted on all conventional systems ; its main function is to avoid that pressure grows to a dangerous point as a result of particular heat exchanging conditions .While the function of the pressure regulator was to disengage the compressor via an electromagnetic coupling , should the system pressure exceed the value of 18 Atm. ,the isobaric valve reduces progressively the efficiency of the compressor.This isobaric valve is installed right on the compressor replacing a cock and connected to the line that leads to the evaporator, its shutter being directly controlled by the compressor’s delivery pressure. Therefore, higher the temperature, lower will be the quantity of circulating Freon. This means that even in the worst various heat exchanging conditions, the compressor will continue to work and the conditioning system will flow out a quantity of cold air proportionate to the warm air eliminated by the compressor. The valve is equipped with a pressure switch disengages the compressor, should the pressure drop because of a leak.

    Regards.
     
  4. thecarnut

    thecarnut Formula 3

    Apr 22, 2006
    2,328
    Atlanta
    Full Name:
    The Car Nut
    "The Isobaric valve replaces the pressure regulator, fitted on all conventional systems "

    This statement is confusing since I have never seen an AC system with a pressure regulator. Most have a binary switch which turn the compressor off if the pressure is too low or too high. Still do not know how to bench test the isobaric valve and I can see how this valve could be a failure point. I am inclined in eliminating the valve and using a binary switch.

    Ivan
     
  5. boralogist

    boralogist Formula Junior

    Jun 21, 2005
    461
    Hello---

    I think Maserati is referring to this internal compressor component which Maserati replaced with the external Isobaric valve unit in our cars:

    Evaporator Pressure Regulator (EPR)
    The evaporator pressure regulator valve, a fully automatic suction pressure control device, is used in certain automotive air conditioning systems. It is located inside the compressor and just under the suction side service valve.
    The valve maintains the evaporator pressure between 152 kPa to 179 kPa and thus its temperature is just above freezing. Inside the valve, the control spring pressure and the evaporator refrigerant pressure maintain a balance. A diaphragm seals the chamber and prevents refrigerant leakage. An increase of evaporator pressure causes the control spring to move the valve away from the seated position and as a result there is an increase in the refrigerant flow from the evaporator to the compressor. Similarly, a decrease in evaporator pressure restricts the flow of refrigerant from the evaporator so that the evaporator pressure increases until the evaporator pressure regulator valve opens. Opening and closing of the valve continues until a balance is established between the evaporator pressure and the spring tension. The valve then remains in a constant position unless the evaporator heat load or the compressor speed changes, and a new balance of pressure is required. Any malfunction of the valve requires replacement as it cannot be repaired.

    Regards.
     
  6. thecarnut

    thecarnut Formula 3

    Apr 22, 2006
    2,328
    Atlanta
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    The Car Nut
    Uhmm .... never heard of Maserati modifying the York compressor. Most likely the valve is in addition to what York provides internally. As we know, if there is a blockage or the system works without proper condenser ventilation the system pressure can increase to unsafe pressures. Normally a binary switch is used. The isobaric valve sounds like a good idea if everything is working properly. The question remains; how to bench test this valve?

    Ivan
     
  7. boralogist

    boralogist Formula Junior

    Jun 21, 2005
    461
    My Bora has gone through 3 compressors etc etc in 33 years of ownership---but the isobaric valve has never been an issue.
    What symptoms have led you to question the health of the isobaric valve?
     
  8. boralogist

    boralogist Formula Junior

    Jun 21, 2005
    461
    PS---I would also suggest you talk to Stuart at MIE---from time to time they have rebuilt isobaric valves for sale on their website.
    Obviously they have a source that rebuilds these valves---would be worth talking to him!

    Regards.
     
  9. staatsof

    staatsof Six Time F1 World Champ
    Silver Subscribed

    Mar 13, 2005
    66,157
    Fuggetaboutitland
    Full Name:
    Bob
    My Bora didn't come with one of these and indeed it's also not in the parts catalog either. But I do have one on my Espada which came with an Italian knockoff from the day of the Tecumseh compressor and I have not tried to get the AC working on that car as yet. I will be replacing it with a Sanden and using the high/low switches to limit the compressor. I see no reason to try and use it except for this ...

    The one on my Espada has integral turn off valves to seal the rest of the system if you need to replace the compressor or pull the engine out and you don't want to crack open the entire system again.
    I don't know if the one Maserati allows for this but I can think of times when I wished I had this option. Especially now that recovery of old refrigerant is mandated. If your compressor failed then you probably need to evacuate, flush and test the entire system anyway. But for systems recently restored perhaps not.
     
  10. thecarnut

    thecarnut Formula 3

    Apr 22, 2006
    2,328
    Atlanta
    Full Name:
    The Car Nut
    This is on a Kyalami that does not have any refrigerant. The system is holding vacuum but I have no idea as to the condition of its components. I plan to flush the lines, replace the compressor oil with ester oil, replace the drier, charge it up and see what happens. Still inclined to get rid of the isobaric valve and use a binary switch on the drier.

    Ivan
     
  11. boralogist

    boralogist Formula Junior

    Jun 21, 2005
    461
    Fair enough!
    Don't forget a NEW Expansion Valve.

    Regards.
     

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