Low pressure switch ?

Tony Tee · Jun 6, 2021

69 dodge charger question? Does the receiver drier low pressure switch get wired between the bulkhead connector and the a/c compressor? I can't find info in my factory service manual. Plus the manual shows a receiver drier without the pressure switch, that has a window/viewport... My receiver drier has a switch with the window.
Do I have the wrong receiver/drier? And don't need the switch?

pnora · Jun 6, 2021

Yes. Power passes through the bulkhead to the low pressure switch. Then from the low pressure switch to the compressor clutch.

kramer · Jun 6, 2021

I don't believe the 69 Charger has a low pressure switch on the filter drier nor do does it have a low pressure switch since that system uses an (EPR valve) evaperative pressure relief valve inside the compressor that regulates the pressure instead of cycling the clutch to do it. I believe the only systems in those years that use a low pressure switch is the A Bodys since they don't use the EPR valve.

pnora · Jun 6, 2021

I might not be correct on the wiring. 69 may not of had a low pressure switch.

pnora · Jun 6, 2021

To the poster. Is this a factory system or a add on aftermarket kit?

R413 · Jun 6, 2021

Your 1969 car never had a low pressure switch, that’s why you can’t find it in the diagram.

Tony Tee · Jun 6, 2021

pnora said:
To the poster. Is this a factory system or a add on aftermarket kit?

It's a factory a/c system that has a semi truck compressor that supposed to have a built in EPR Valve. I can't remember the brand of compressor right now. But It's not a sanden for sure.

Tony Tee · Jun 6, 2021

R413 said:
Your 1969 car never had a low pressure switch, that’s why you can’t find it in the diagram.

Thanks! This is all starting to make sense now.

RJRENTON · Jun 7, 2021

kramer said:
I don't believe the 69 Charger has a low pressure switch on the filter drier nor do does it have a low pressure switch since that system uses an (EPR valve) evaperative pressure relief valve inside the compressor that regulates the pressure instead of cycling the clutch to do it. I believe the only systems in those years that use a low pressure switch is the A Bodys since they don't use the EPR valve.

Not exactly correct.....the EPR valve (Evaporator Pressure Regulator) controls the suction pressure of the evaporator by throttling the compressor's inlet pressure to a value of 35-38 psi of the evaporator to prevent freezing of the collected condensate on the air side of the evaporator. Used in conjunction with the thermostatic expansion valve on the evaporator's inlet side to maximize cooling, without icing, by controlling the superheat temperatures. In the old systems, the pressure switch on the receiver/dryer was a normally closed switch, that opened to break clutch coil current, if pressure got too high. Later, the switch was changed to a normally open switch, held closed if there wss sufficient refrigerant in the system; it opened if refrigerant was lost due to a leak. I believe that ALL Chrysler A/C systems using the RV-2 compressor used the EPR valve and TXV valve to regulate refrigerant flow. Perhaps aftermarket A/C systems (dealer installed) were different.
BOB RENTON

Demonic · Jun 20, 2021

Kramer was mostly correct, except about the abbreviation of EPR, which Bob is correct about.

But yes, in short, no low pressure switch 69 and earlier B body. This can have the unfortunate side effect of pulling the low side into a vacuum. If there's a leak, the system can introduce air into itself. A minute amount usually, but remember air and moisture is bad inside the system. Clean and dry is the word. You could wire in the switch, most have a sufficient deadband to prevent short-cycling. The real question is, can the switch handle the current draw of the electromagnet clutch? The FSM has the current draw figures.

Tony Tee · Jun 20, 2021

I have a v5 Harrison compressor . Its supposed to have a built in EPR valve of some sort .Semi truck application. The mounting ears are similar to the sanden compressor. And it fits great! and the double pulley belts align up nice. Been trying to find another compressor just like it but I think it's a one of a kind compressor. Any experts on the V5? Will I need the low pressure switch with the V5 ?

RJRENTON · Jun 21, 2021

Tony Tee said:
I have a v5 Harrison compressor . Its supposed to have a built in EPR valve of some sort .Semi truck application. The mounting ears are similar to the sanden compressor. And it fits great! and the double pulley belts align up nice. Been trying to find another compressor just like it but I think it's a one of a kind compressor. Any experts on the V5? Will I need the low pressure switch with the V5 ? View attachment 1127285

I had an Oldsmobile with automatic temperature control system....set a temp and the system will hest or cool to maintain the set point temp. The system used the Harrison V-5 compressor. This compressor is a 5 cylinder double acting design (the -5 number) and the V signifies a VARIABLE DISPLACEMENT DESIGN, using a swash plate to vary the piston stroke as the swash plate rotated. The variable device was a sort of the equilivant to the EPR valve which conttolled the swash plate angle and compressor's displacement, adjusting the suction pressure to maximize the cooling by keeping the superheat temperature at the optimal value and preventing evaporator icing. The system performed very well. As system demand changed, the compressor's swash plate angle seamless changed the displacement....IOM, a great design.....but then along came R-134A refrigerant.....and the rest is history.....
BOB RENTON

Low pressure switch ?

Tony Tee

Well-Known Member

pnora

FBBO Gold Member

kramer

Well-Known Member

pnora

FBBO Gold Member

pnora

FBBO Gold Member

R413

Well-Known Member

Tony Tee

Well-Known Member

Tony Tee

Well-Known Member

RJRENTON

FBBO Gold Member

Demonic

Well-Known Member

Tony Tee

Well-Known Member

RJRENTON

FBBO Gold Member

Similar threads