Isobaric valve

Were the York components shared with Citroen-era Maseratis? If so, look up Dave Burnham and give his shop a call...?
- Art

 

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.

 

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.

 

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?

 

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.

 

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.

 

Fair enough!
Don't forget a NEW Expansion Valve.

Regards.