Ok, I just found out that the poa elimanator is nothing but an open tube with adjustable pressure switch. The best anyone has been able to get is a vent temp of 50 degrees. The other option is have your old poa rebuilt which takes 6 weeks.
My question is will the later evaporator and accumulator for the orifice system fit in the earlier case? Same with condensor. Does someone make a tube to replace the dryer? Or do I have to replace the condensor? Any input by someone that has made the change would be appreciated.

 

That adjustable pressure switch is to change the system over to a pressure cycling system. You will also need to add an orifice valve. It just needs to right before but close to the evaporator. There are generic parts to do this, you do not need a specific vette part. Existing evaporator and condensor should work. A 50 degree vent temp probably means a heat soaked / too small condensor, which would be easy to verify with gauges and a IR temp gun. A parallel flow condensor almost always improves system hot weather performance. You really can not have too big of a condensor. Especially in an airflow restricted corvette.
https://www.ackits.com/

 

Is your current POA valve bad?

 

I recently rebuilt the orifice tube system on my 78, which I imagine would be very similar to rebuilding your system with a POA eliminator. I used a variable orifice tube, a standard condenser and R4 compressor and it's filled with R134a. Vent temps range between 40F and 45F depending on conditions. I think it could be even better with a parallel flow condenser and some insulation around the evaporator box which gets a lot of heat from the exhaust.

 

i have (had) the next newer version. the VIR. i was under the assumption the 68-72 POA "update" also replaced the expansion valve with an orifice setup. apparently this is not so?

 

as far as OP's question will the 78 evap fit, i put it into my 75 box. doing my own VIR eliminator. the orifice mounts in the inlet line of the evap unit. THE HOSE ENDS WERE BOTH DIFFERENT SIZES FROM ORIG! my suction-condenser hose combo was blown out so i just bought 78 hose set to match the 78 evap. universal type accumulator with several diff pipes made connection the suction side easier. but the liquid line from the condenser to the evap was also different. i tried to change ends and splice it. no workee so good. so if you want to change to 78 setup you will need suction hose and liquid lines. the suction hose is one of the main fail points in 50 year old AC unit so no great loss. the liquid line is about 100 bucks and a little irritating cuz it does not wear out. the condensor from the 75 took the same line ends as the later one. i believe also same as the 72 setup. but the condenser i bought does say 74-82 so it may require some more homework. and i do not see how leaving the drier and sight glass in the system would be a bad thing either.

 

OK let's try some pics:

Here is a really good video on POA valves:

Here is a POA eliminator kit that at least looks original:
https://www.ebay.com/itm/193877603112

It appears that these POA eliminators maintain the original expansion valve. That part is really just a mechanically controlled variable orifice and is actually superior to a fixed orifice, as long as dirt does not make it get "stuck". IMHO I would just pop a new one in if you want this modded system to work well.
https://www.zip-corvette.com/63-72-a...EaAon8EALw_wcB

The receiver/drier should be replaced anytime the AC system is open for a time, or on a switch from R12 to R134. It contains the dessicant, gets water saturated quickly, and the type of dessicant used on R12 will deteriorate with R134.
https://www.ecklerscorvette.com/1968...-103150-1.html
(on sale at Eklers today).

When you buy a POA eliminator kit (pressure bypass system), you must get one designed for either R12 or R134, or one with an adjustable pressure switch, because R12 needs to be set at 30psi and R134 needs to be set at 21psi. Yes it does just appear to be just an open tube. The POA valve has an extra line which will bypass the evaporator to keep it from freezing up, where a pressure switch will just turn off the compressor to accomplish the same thing, and is not as prone to getting stuck. (If you are switching to R134 you must replace the POA valve anyway to get the pressure setting correct.)

Here is a pic of a 1971 vette wreck from our shop, the top circle is the POA (pressure bypass) valve and the bottom circle is the expansion valve. (It's turned on it's side, normal up is to the right in this pic) These components are located on the left side and outside of the AC box on the car. They can both be accessed and/or replaced without opening the AC box. So I would not use later C3 parts, I would use the direct replacement POA eliminator kits) (You can see some remaining pieces of the fiberglass AC box.)


If "someone" was not able to get under 50 degree vent temps they did not do something correct. Most likely they used the 30psi pressure switch setting instead of the 21psi required for R134. That would keep the system from ever getting very cold. 2nd possibility is if it was cold when driving, but got warm in traffic or low airflow, then either the fans or the parallel condensor need to be upgraded. If the engine is not overheating the fans are not the problem, it would be the condensor. Their is NO reason for it not to be COLD if done properly. Their is zero reason to replace the evaporator radiator above, unless it is leaking. I recommend testing the system FIRST and see if it will hold vacuum for a long time.

I buy all my AC parts from one of these three huge AC outfits: Arizona Air, ACKits, or Original Air. You need their expertise to get it "right".

 

POA Valve Testing

 

Good advice here for sure.