Expansion Valve and 'Front or Rear'

[Nxcoupe]

Looking for a new Expansion Valve for my 66 Coronet 500 361 V8 with factory air and they say Front or Rear, which makes no sense to me. Anyone care to 'splain it to me? I want to get a new one as my pressures weren't far enough apart, low to high side, figured the valve is stuck. I'm looking on Rock Auto.
Thanks!

 

[69Bee]

My money is on "They don't know what the hell they are talking about", just like autozone counter people... Your car only has one expansion valve because it isn't a minivan with a "Dual Zone AC"!!

 

[Nxcoupe]

A picture is worth a thousand words......

 

[69Bee]

So, looking at the pictures, and my past experiences with my AC, this is my best "Edumigated Guess":

Both expansion valves attach to the same spot, BUT where the sensing tube/bulb determines valve operation at different points.

1) Front has just a closed tube (Capillary tube) and is attached with tape and/or a putty to the aluminum part of the freon hose to the compressor to determine expansion valve operation.
2) Rear has the "Sensing Bulb" which is attached to the evaporator to sense temp to determine expansion valve opertion.

You need to establish which valve you have by locating the sensing Tube/Bulb to determine which valve you have.

Dave

 

[Nxcoupe]

So, looking at the pictures, and my past experiences with my AC, this is my best "Edumigated Guess":

Both expansion valves attach to the same spot, BUT where the sensing tube/bulb determines valve operation at different points.

1) Front has just a closed tube (Capillary tube) and is attached with tape and/or a putty to the aluminum part of the freon hose to the compressor to determine expansion valve operation.
2) Rear has the "Sensing Bulb" which is attached to the evaporator to sense temp to determine expansion valve opertion.

You need to establish which valve you have by locating the sensing Tube/Bulb to determine which valve you have.

Dave

Makes perfect sense! Thanks! I will look in the morning.

 

[69Bee]

My '74 Charger had the front tube that went into a hole in/on the aluminum part of the hose in the engine compartment, and my '69 Bee had the tube that went to the evaporator in the unit. Your pic and I went to RA to study the pics and they shook the dust off some OLD memories of things I had seen in the past. Good luck with it.

 

[1 Wild R/T]

Seriously on a Mopar using the RV2 compressor before jumping to any conclusions let's talk about the STV or EPR valve & where you are reading the pressures at...

There's more than one port on the low side of Mopars.. One is reading the evaporator pressure & one is reading the true low side after the STV/EPR valve.... The evaporator pressure isn't gonna read as low as the true low side...

STV is the Suction Throttling Valve
EPR is Evaporator Pressure Regulator

They both do the same thing, just in a slightly different way... Engineers like to try different stuff... They maintain the evaporator pressure when the system is undercharged to prevent the evaporator freezing...

The true low side port is on the passenger side head of the compressor, the Evaporator Pressure Port is on the manifold bolted to the back of the compressor...

THE STV/EPR is located in the suction port of the compressor, it's just slid into the port and captured by the manifold... Remove the two allen bolts & pull the manifold... When the EPR/STV fails it'll read like a bad Expansion valve

I doubt you can find a new STV/EPR valve but you can simply take it out & the system will work like a typical A/C system...

 

[Nxcoupe]

Seriously on a Mopar using the RV2 compressor before jumping to any conclusions let's talk about the STV or EPR valve & where you are reading the pressures at...

There's more than one port on the low side of Mopars.. One is reading the evaporator pressure & one is reading the true low side after the STV/EPR valve.... The evaporator pressure isn't gonna read as low as the true low side...

STV is the Suction Throttling Valve
EPR is Evaporator Pressure Regulator

They both do the same thing, just in a slightly different way... Engineers like to try different stuff... They maintain the evaporator pressure when the system is undercharged to prevent the evaporator freezing...

The true low side port is on the passenger side head of the compressor, the Evaporator Pressure Port is on the manifold bolted to the back of the compressor...

THE STV/EPR is located in the suction port of the compressor, it's just slid into the port and captured by the manifold... Remove the two allen bolts & pull the manifold... When the EPR/STV fails it'll read like a bad Expansion valve

I doubt you can find a new STV/EPR valve but you can simply take it out & the system will work like a typical A/C system...

View attachment 1705440

Great info. So does this valve just slide in and out or screw into the inlet port? It's wierd, because when I initially charged it last year or so, everything read as it should. I topped it off this year and it was reading 60 to 70 on the low side, and 200 on the high. With the temp being what it was that day, it should have been around 30 to 40 in low side and 275 on the high. It still would chill beer inside but with all the mopars I've charged this one is not behaving normally.
I'll get pics under the hood of the compressor and expansion valve.

 

[1 Wild R/T]

Like I mentioned, it's just slid into the port and captured by the manifold... And as it turns out I was wrong, they can be found....
The Part Guy - A/C Valves (Suction Throttle, POA, VIR, Expansion Valve)

 

[Krooser]

Mopar offered "rear air" on certain Monaco, Polara and Chrysler station wagons.

I was an A/C tech at a Dodge dealer '68-'69.

That option was popular with people with show dogs that were crated in the back of the wagon. Summer heat, especially in the South and Southwest was brutal on the cargo area of those wagons.

We also had a couple customers that used their wagons for flower deliveries, some food deliveries, etc. They had rear a/c, too.

A rare option.

I was servicing a black Monaco wagon with dual air that had a freon leak. My stalls were close to the service writers desk and the managers office.

I got this wagon jacked up high on the right side to check for leaks in the hoses that ran alongside the right rocker panel.

Just as I got my head under the rockers the high pressure line exploded!

Sounded like a bomb!

My service manager dove under his desk...the shop cleared out. I crawled out from under the car covered with refrigerant oil.

Seeing my manager, who was a ringer for Superman, crawl out from under his desk was priceless!

 

[gtx6970]

Imo. Try to find an nos mopar epr valve if needed

Most of the aftermkt ones either don't work.....or don't last long

 

[gtx6970]

Otherwise.i used one of these with no issues

 

[Nxcoupe]

Here are pics of my set up.

 

[RJRENTON]

Like I mentioned, it's just slid into the port and captured by the manifold... And as it turns out I was wrong, they can be found....
The Part Guy - A/C Valves (Suction Throttle, POA, VIR, Expansion Valve

EXCELLENT SOURCE OF PARTS. IMO....the Mopar Thermostatic expansion valve (TXV) controls the liquid refrigerant entering the Evaporator while at the time is looking at the exiting evaporator refrigerant temperature , to try and maintain constant evaporator conditions...enough refrigerant volume to provide adequate cooling; the pressure function helps to prevent excessive refrigerant flow at highway speeds by throttling the refrigerant flow to prevent icing. This is equates to a pressure/temperature balanced valve. The EPR VALVE (Evaporator Pressure Regulator) in the compressors suction port helps to maintain a relatively constant evaporator pressure with varying rpms and helps to prevent evaporator icing. Remember the lower the suction pressure, usually results in evaporator icing (assuming an adequate refrigerant charge initially). I usually charged the system, following FSM procedures using the Schrader valve on the RV2 head and not the EPR connection and charge to a clear sight glass on the dryer. ......just my opinion of course.....
BOB RENTON

 

[Nxcoupe]

EXCELLENT SOURCE OF PARTS. IMO....the Mopar Thermostatic expansion valve (TXV) controls the liquid refrigerant entering the Evaporator while at the time is looking at the exiting evaporator refrigerant temperature , to try and maintain constant evaporator conditions...enough refrigerant volume to provide adequate cooling; the pressure function helps to prevent excessive refrigerant flow at highway speeds by throttling the refrigerant flow to prevent icing. This is equates to a pressure/temperature balanced valve. The EPR VALVE (Evaporator Pressure Regulator) in the compressors suction port helps to maintain a relatively constant evaporator pressure with varying rpms and helps to prevent evaporator icing. Remember the lower the suction pressure, usually results in evaporator icing (assuming an adequate refrigerant charge initially). I usually charged the system, following FSM procedures using the Schrader valve on the RV2 head and not the EPR connection and charge to a clear sight glass on the dryer. ......just my opinion of course.....
BOB RENTON

All opinions are welcome. I appreciate your input. I am always hesitant to charge to the head port as it can easily break the compressor if liquid gets into it.
I have been using my old R12 gauges to charge it, but I believe I am going to get R134 fittings and use those gauges because of the excessive loss of refrigerant when unscrewing the gauges from the ports. I want to be able to remove the 134 fittings afterwards and keep that original look to the system.

 

[RJRENTON]

All opinions are welcome. I appreciate your input. I am always hesitant to charge to the head port as it can easily break the compressor if liquid gets into it.
I have been using my old R12 gauges to charge it, but I believe I am going to get R134 fittings and use those gauges because of the excessive loss of refrigerant when unscrewing the gauges from the ports. I want to be able to remove the 134 fittings afterwards and keep that original look to the system.

I've ALWAYS GAS CHARGED the RV2 thru the head port. The EPR valve will close down slowing the charge time. My gauge/charge set has a expansion chamber to extract liquid from the tank and meter it slowly into the charge port preventing slugging of the compressor...
BOB RENTON