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Chris, if your A/C R12 system in your MK2 is intact, usually a can or 2 of oil conditioner will restore the system for a daily driver... I have performed this maintenance on at least 4-6 Mk2 will great results...
 

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Hi All, new to this board. Have Had 2 MK 2's and 2 Mk 3's, Currently have a MK2 1984 Automatic. 86000 miles. Just bought it. Had no working ac when I bought it. I have just finished installing A new Expansion Valve, Receiver /Drier with sight glass, EPR, green o rings on all fittings, I flushed system with a flush kit backwards and forwards, pulled compressor to flush separately, flushed all lines when I had them apart to install o rings. When I was sure it was all clean inside, and there was no oil in the compressor, receiver, evaporator, or condensor, I pulled a vacuum to 28 for 4 hours, and let it sit overnight. No Pressure loss, so I filled with fresh Mineral oil 7.5 oz, and 1.7 lb new R12. Sight glass shows clear at 1000Rpm,s and mostly clear at idle about 650 rpm's. Just a slight waver off and on in the glass at idle. At the center vent I am getting about 45 degrees on a 90 degree day. I kinda felt it should be a bit colder like around 38 degrees at the vent. I read Jims article a few times, and in it he states that the epr is adjustable, but I can not find any way to adjust the epr in the tsrm. Does anyone here know anything about adjusting the epr.
Thanks for Listening. Semper FI
 

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I read Jims article a few times, and in it he states that the epr is adjustable, but I can not find any way to adjust the epr in the tsrm. Does anyone here know anything about adjusting the epr.
Thanks for Listening. Semper FI
I would like more details on operation of the EPR as well. From my limited understanding, it appears that this is a back pressure regulator that opens or closes based upon feedback from the Expansion Valve feedback line.


Expansion Valve - The capped brass nut is the pressure feedback that goes into the EPR.

The system as used on the supra does not monitor the Evaporator temperature, rather it monitors the pressure at the Evaporator. If the pressure at the expansion nozzle starts to increase, the pressure will exert pressure on the diaphragm of the EPR which will override a preset coil spring tension to close the EPR outlet. This reduces the flow of the gaseous gas running through the suction line back to the inlet of the compressor. As the volume of gas is reduced, there is less gas to convert back to liquid and the pressure of the high side liquid is reduced. As a result the supply pressure to the expansion valve is reduced, the amount of cooling is reduced.


This is a negative feedback loop that constantly adjusts the pressure to maintain a constant (or maximum value).


Close up of the EPR Valve

EPR Pressure Adjustment Screw.jpg
Adjustment screw on the end of the EPR.

The spring which is factory adjusted to a preset pressure is adjustable. If you look at the end of the housing, there is a straight blade adjustment screw with red thread locker and a jamb nut.

The screw adds or removes spring preload. If you thread the screw in clockwise, you are increasing the spring preload. This spring holds a diaphragm and plunger open. When the Evaporator pressure starts to equal the value of the spring, it starts to push the diaphragm shut which moves the plunger into an orifice, reducing the orifice cross section which effectively plugs the return line. Adding preload means more pressure is required to force the plunger shut. Removing preload means that less pressure is required to push the plunger into the orifice to reduce gas flow.

I don't think you want to change the preload much. You could easily cause the Evaporator to freeze if you go too far.

Having said all this, I have never had an EPR apart. Take this all with a grain of salt. This is how most back pressure regulators work.
I would love to see an EPR disassembled.

Dale
 

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Having a chance to think about this a little more, I would like to highlight something that JDK mentioned.

As you increase the High Pressure-side pressure, the increased pressure at the Expansion Valve orifice causes increased gas expansion and therefore a larger temperature drop. If the temperature at the valve drops too much, moisture in the Evaporator could freeze, blocking the refrigerant flow in the nozzle. I assume that the receiver-drier should remove moisture in the system, but I guess that over time it becomes less effective and should be changed.

If this happens, either the refrigerant flow is blocked by the frozen orifice itself, or to prevent an over pressure situation, the EPR closes to reduce the flow of refrigerant returning to the compressor. If this continues, the compressor lubricating oil which is carried in the refrigerant will be reduced, damaging the compressor itself.

The point being, if you increase the EPR pressure too much you risk damaging other components.

Adjust this valve carefully!
 

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Hi all, thanks for the info. Now i understand the tsrm expansion valve check procedure. Will have to recheck my pressures at 2000rpm’s. Using the epr adjustment you can fine tune pressures for max evap core temps. I’ll have to look closer for the adjusting screw. Try to get 30-35 psi low side with 185 - 213 psi on high side at 2000 rpm’s, With R12. Other refrigerants will be different. May wind up with lower than 30-35 psi on low, but need to keep it out of the freeze pressures.
Thanks again. Semper Fi
 

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Supy, Those temp #s are pretty dang good!! I would look into modding the condenser fan better CFMs, cleaning out and sealing the air ducting inside the cabin areas!!

Nice discussion Sir!!
 

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AC temps

Supy, Those temp #s are pretty dang good!! I would look into modding the condenser fan better CFMs, cleaning out and sealing the air ducting inside the cabin areas!!

Nice discussion Sir!!
Thanks AJ, I did a bit more work on it today, tweaked the pressures a bit, and was finally getting 37 degrees at the center vent, it was 94 degrees and humid here today, so I feel like the Condenser is probably doing all it was designed to. Cond fan was going on and off as it was supposed to depending on whether I was moving or at idle. So I am fairly well satisfied that the car is performing just like I remember my 83 did back in 83 when I bought it new. It was designed for R12, and it is now running great back on R12. Whoever had it before me, really mucked it up, by adding 134a, magic freeze, dye pack and a sealer, oh and 10 oz ester oil. No wonder it didn’t get cold. And they never really converted anything over to run on any of those refrigerants. That is why I made doubly sure that the system was clean inside all the components, and replaced certain components before putting the right stuff back in. All that being said, Even though I am getting great airflow through the vents, I suspect you may have a point about looking into the ductwork, as you could hang meat in the glovebox, after an hour of driving with the ac on. I may have to pull that down again, and have a better look at the ductwork near it.
Thanks again—-Semper Fi. Leave no Brother Behind...
 

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Supy, agree 100% R12 is the best to stay with with our generation of Supras...R12 compressor really isn't designed for 134a IMO...

Glad to be of assistance anytime!! PM me or email if needed [email protected]...
 

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Chris here's the link to the A/C tune up FAQ I posted a while back...

Here's my quick A/C tune up I wrote up a few yrs ago...cheap way to see if the R12 system is operational...
https://www.celicasupra.com/forums/s...il+conditioner
Arch,

Dang it, I don't know if it's just me and my abysmal computer skills, or if the link you posted is dead, but is this the link you are referring to?

https://www.celicasupra.com/forums/showthread.php?40622-A-C-Tune-up

This is really useful.

Thank you

Dale
 

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