Where there manual A/C along with ATC

[CBODY67]

You mean "ATC 1" in "Slabs" and "Fusies"???

The first time I walked into a BAP-GEON parts store and saw one of the (obsolete) Chrysler controllers hanging on the wall, I HAD to askCBODY "Why", respectfully. That's when I found out it was also a Mercedes part use. I smiled! Not concerned about ATC 1 or ATC 2, back then. Just the fact that Mercedes found a Chrysler part they liked. But then they also used some ACDelco stuff for memory seats and such later on, too, I believe. Or what that Porsche/Audi back then?

CBODY67

 

[CBODY67]

Go to www.imperialclub.org . Click on the "Literature" icon, then follow the clicks to get to the Chrysler Master Tech Conference page. Scroll down to "1968" and you'll find the Auto-Temp training booklet/film strip. #244, I believe. Continue scrolling down to "1971" and you'll find the similar Auto-Temp II training information.

This is ONE bookmark every Mopar enthusiast needs to have in their Favorites Bar! Kind of hokey with the old filmstrip series format, but that doesn't make the information dated, though. Some of the information might seem a little general, but this information with a factory service manual can be very neat stuff to discover what made Chrysler products so great!

Great reading during the cooler months of the year!

CBODY67

 

[kwf340]

Here's the deal on them for the 21'st century:

Most of the EPR valves ever made are now shot and don't work anymore, with the exception of some that were in cars where the A/C was always serviced and kept alive. A few years ago I was helping a friend get the A/C up and running in his Challenger and his EPR valve was stuck. I ordered three NOS valves, one for him, and two to put in inventory, and they were all bad. The thermal wax inside them just doesn't last forever.

Hi everyone - first post here.

I'm doing some troubleshooting on my AC system and I suspect the EPR or the TXV. Can someone explain to me how the RV2 EPR valve works? What is confusing me is reference above to “thermal wax”. Based on my understanding, the ports open/close based on pressure conditions, not thermal conditions. With that in mind, wouldn’t the valve have some sort of spring to hold the ports closed when suction is low and allows the ports to open when suction is high? What does thermal wax have anything to do with the properties of the ports opening or closing?

Some similar info here (post #4) Forums / General Tech / I'm at the R12/134A crossroads.... - C-Body DryDock

So if its pressure-based as I suspect, wouldn't the ports be closed when out of the system (which would equate to low suction pressure) regardless of the temperature?

 

[Davea Lux]

The EPR valve or Evaporator Pressure Regulator functions to keep refrigerant pressure in the evaporator from dropping too low and icing up the evaporator. It also functions to keep a more or less constant pressure in the evaporator. A constant pressure results in a more or less consistent temperature of the chilled air coming off the evaporator. This allows the blend doors in the evaporator unit to keep the desired temperature that has been set on the unit thermostat. The blending system requires chilled air within a fairly narrow range to function properly. (think of the EPR valve as a thermostat, it works on the same principle).

The purpose of the "thermal wax" is to provide a lubricant of sorts for the internal parts of the valve actuating mechanism and the melting of the wax pellet provides mechanical energy in a pressurized tube to open and close the EPR valve. An R-12 system that has been left discharged or disconnected for an extended period of time allows moisture to get into the A/C system. Moisture degrades the refrigerant oil and eventually by corrosion the thermal wax. This results in the EPR valve becoming seized and non functional. The EPR valve is a non servicable component, so if it is seized, it has to be replaced. They also can go bad if they sit long enough as the wax and its enclosure will deteriorate over time, which is why NOS units are often non working out of the box.

For even more good news, if you are changing refrigerants from R-12 to R-134a, the valve will need to be replaced to one that is rated for R-134a, the refrigerant R-134a does not play well with the thermal wax compound used on the R-12 valve due to different temperature and pressure characteristics of the R-134a. And if the valve was not seized already, it probably will be in short order after the conversion. When a lot of these units were being converted, the replacement valves were available, but now, these units are pretty rare and parts are hard to come by as they are now obsolete and no longer stocked.

Good luck

Dave

I edited this post to make it more clear

 

[kwf340]

Thanks Dave. So the "thermal wax" is (more or less) just a lubricant and has nothing to do with when the ports open/close. That makes sense.

Is there anyway to test the EPR when out of the system? I know the service manual says to not handle the valve more than necessary, which implies they are delicate/easily damaged.

Ken

 

[Davea Lux]

Thanks Dave. So the "thermal wax" is (more or less) just a lubricant and has nothing to do with when the ports open/close. That makes sense.

Is there anyway to test the EPR when out of the system? I know the service manual says to not handle the valve more than necessary, which implies they are delicate/easily damaged.

Ken

The thermal wax is both a lubricant (It keeps the metal parts that power the valve from chafing) and it also powers the valve to open and close. The wax is contained usually inside of a capillary of some sort. As the wax melts from an increase in temperature, pressure inside the capillary increases, the increase in pressure is used to power the valve usually by means of a sealed bellows of some sort, some systems also use a small piston. The type used with the Mopar ATC and standard air is fragile and not really designed to be handled. (the capillary will break off or spring a leak) Most of the time when the valve is stuck, it is because the capillary has been breached by corrosion or physical damage to where the wax vents out of the capillary when heated. The best way to test the valve is with it installed on the system. If it is stuck, the head pressure on the compressor will rise to the point that the limit switch for high pressure will shut down the compressor or the compressor will shut down on low head pressure, this is call a short cycle. This assumes the system is fully charged. Service manual gives detailed pressure checks for a working or non working valve.

Dave

 

[5wndwcpe]

Okay, so now I'm a bit confused. I thought the EPR ( evaporator pressure regulator) was used on the manual system and modulated the refrigerant flow whereas the ETR (evaporator temperature regulator) was used on the ATC system and started and stopped refrigerant flow via a solenoid.

If the valve is considered suspect, the service manual directs you to apply 12vdc to the wire connected to the ETR and listen for the audible solenoid action.

 

[Davea Lux]

Okay, so now I'm a bit confused. I thought the EPR ( evaporator pressure regulator) was used on the manual system and modulated the refrigerant flow whereas the ETR (evaporator temperature regulator) was used on the ATC system and started and stopped refrigerant flow via a solenoid.

If the valve is considered suspect, the service manual directs you to apply 12vdc to the wire connected to the ETR and listen for the audible solenoid action.

Both systems use an EPR valve or TXV (Expansion valve) can't have functioning A/C without one. The ETR valve is a small electric solenoid that hooks to the back of the A/C compressor and it is only used with Automatic Temperature control. Your test methodology for this valve is correct, the valve should click if 12V is momentarily applied to the valve pin. A solenoid operates the valve which turns off or turns on the refrigerant flow at the compressor to gain better control of the suction gas coming off the evaporator.

Dave

 

[Davea Lux]

Thanks Dave. So the "thermal wax" is (more or less) just a lubricant and has nothing to do with when the ports open/close. That makes sense.

Is there anyway to test the EPR when out of the system? I know the service manual says to not handle the valve more than necessary, which implies they are delicate/easily damaged.

Ken

If you are planning to remove the EPR or TXV, be very careful when doing so. After 40-50 years, a lot of them have seized mounting threads which can ruin the evaporator if you get too rough with it. Sometimes necessary to take a propane torch to the nut holding the valve on to free it up. BE SURE THE SYSTEM IS DISCHARGED FIRST!
It is possible to test the valve off the car. Put a small block of dry ice on the end two or 3 inches of the capillary, this should make the valve close up. Remove the dry ice and let the capillary warm up, the valve should reopen after a short while.

If you have a charged system, another cause for the valve failing to function is moisture contamination. Water in the system will freeze as it goes thru the expansion valve and either make it stick or plug it up tight. If that is the case, the system will need to be evacuated, a new charge of oil installed and a new filter dryer installed before you can proceed further.

Dave

 

[5wndwcpe]

If you are planning to remove the EPR, be very careful when doing so. After 40-50 years, a lot of them have seized mounting threads which can ruin the evaporator if you get too rough with it.

I think you mean the TXV, no ?

The EPR should be in the RV2.

 

[Davea Lux]

I think you mean the TXV, no ?

The EPR should be in the RV2.

The ETR is the one in the RV2 yeah it sounds *** backwards, but that is where it is. Evaporator Temperature Regulator measures the suction line temp and regulates the flow based on how hot or cold the return gas is coming into the compressor. Evaporator Pressure Regulator or TXV (Thermal Expansion Valve, EPR are the same thing, just different terminology, Mopar calls it an EPR, everyone else calls it a TXV ) is located next to the evaporator.

Dave

 

[5wndwcpe]

You then install a universal temp sensing switch on the evaporator that cycles the compressor when needed.

Jeff, do you have a source for these ?

 

[5wndwcpe]

I was curious as to why they choose to use two different valves (EPR/ETR) and came across this in a 1970 fsm.


This E T R (evaporator temperature regulator)


control was chosen for the Auto-Temp system because


the E P R used on Standard A / C cars would not


prevent coil freeze-up at the lower ambient temperatures


at which the compressor is required to operate.

 

[commando1]

This thread is making my brain cells bleed.

What is this? ETR, correct? And it's used where??

But then I found this pic which effed me up even more

 

[5wndwcpe]

The top picture is the ETR gasket which sits between the low pressure line and the RV2. Notice also the spade terminal for the electrical connection to activate/deactivate the solenoid. Here is a picture of an ETR valve, p/n 2837402, pirated from eBay.

 

[kwf340]

Yeah I’m confused too. It seems that the EPR (evaporator pressure regulator) valve and TXV (expansion valve) are being referred to as one in the same, which I don't get from the service manual. Based on my understanding, the EPR valve is located in the suction port of the RV2, not next to the evaporator. The pic in the previous post (called an ETR) is what my EPR valve looks like. The service manual shows it like this (there are variations of the design but they have the same general shape).

This pic from the service manual shows the EPR valve in the RV2 suction port (red text added to clarify).

And this pic from the service manual shows the EPR valve being removed from the suction port of the RV2.

The expansion valve (TXV, which is different from the EPR valve) is located next to the evaporator and is connected between the liquid line and the inlet of the evaporator.

So from what I see the TXV and EPR are different. Am I missing something?

 

[Davea Lux]

Yeah I’m confused too. It seems that the EPR (evaporator pressure regulator) valve and TXV (expansion valve) are being referred to as one in the same, which I don't get from the service manual. Based on my understanding, the EPR valve is located in the suction port of the RV2, not next to the evaporator. The pic in the previous post (called an ETR) is what my EPR valve looks like. The service manual shows it like this (there are variations of the design but they have the same general shape).
View attachment 191569

This pic from the service manual shows the EPR valve in the RV2 suction port (red text added to clarify).

View attachment 191570

And this pic from the service manual shows the EPR valve being removed from the suction port of the RV2.

View attachment 191571

The expansion valve (TXV, which is different from the EPR valve) is located next to the evaporator and is connected between the liquid line and the inlet of the evaporator.

View attachment 191572

So from what I see the TXV and EPR are different. Am I missing something?

 

[Davea Lux]

The '70 Chrysler service manual refers to the same valve as an ETR (section 24-62) I don't know which one is right, might be a misprint in one manual or the other. I am getting a headache. Looking at some of the other literature from online, I am inclined to agree that the proper terminology is EPR. Sorry about the confusion.

Dave

 

[commando1]

I knew it.
It wasn't me.

 

[kwf340]

The '70 Chrysler service manual refers to the same valve as an ETR (section 24-62) I don't know which one is right, might be a misprint in one manual or the other. I am getting a headache. Looking at some of the other literature from online, I am inclined to agree that the proper terminology is EPR. Sorry about the confusion.

Dave

Yeah I see it now. For auto temp systems one section of the manual refers to an ETR valve at the evaporator and another section of the manual refers to an "ETR" valve at the compressor (non-auto temp systems refer to only an "EPR" valve in the compressor). The manual also describes testing the ETR valve (the one in the compressor) by applying 12 volts to it - which makes me think that while both the EPR and the ETR control suction pressure, they do so in somewhat different ways.

So revisiting my original questions about the "thermal wax" (post 23), how does the EPR valve (in the compressor) operate? Is it strictly controlled based on pressure or is there a thermal component (thermal wax)? Is there any way to test the EPR valve out of the system?

Thanks and sorry for any confusion i may have created.