All,
I have a 1970 Cutlass SX Convertible that I did a frame off restore/rebuild. I've not been able to get the A/C to cool correctly since rebuilding. I've replaced the compressor with a re-built A6 pump, replaced the condenser, dryer, expansion valve, sent out the POA valve to have re-built and calibrated for R-34A refrigerant. It has alll new A/C lines on it. It seems like I can never get the adequate amount of R-34 in before my pressures on the high side reach their maximum for the temperature (Usually about 28 oz of refrigerant.). Low side pressure runs about 24-25 psi. The bypass line for the expansion valve to the POA covers with frost, so it seems it is bypassing too much refrigerant, the line top line off the evaporator is only cool to touch, it never gets cold. Could my evaporator be partially plugged? before re-assembly, i had the evaporator pressure tested but not any boil out or flow testing done. I've replaced the expansion valve once thinking maybe there was something wrong with that, but new replacement expansion valve displayed the same results. Any ideas???
Al

 

Are you sure you don’t need a different condensor for the R134A? It didn’t exist when the factory built your car.

I’m still using Freon in my ‘66, who knows for how much longer. Frankly I’m shocked that these old components work as well as they do.

From what I’ve learned, if the system isn’t balanced between condensor, evaporator and demand, the evaporator can get too cold, plug up with ice and not work right. Sounds like the cooling part is working. I wonder if it’s “too good”?

Respectfully, a rank A/c amateur,
cf

 

When doing this do you have a fan blowing across the radiator/condenser so there is adequate air flow?

 

what is the pressure on the high side? Once you start the system, how long before it gets too high or kicks out?

 

Actually, I did originally recharge with r-12, and had similar result. I switched to r-34 as the costs of troubleshooting with R-12 are prohibitive, (I don't have a collection system to recycle it). I don't think it is icing up, as it never gets cold, just cool on the output of the evaporator line, but I suppose it is possible that something like that could be happening. I'm reaching out as my next step is to remove the evaporator coil, which is very difficult on a car with a 455 ci engine. thanks for your input

 

Kenneth,
I have the factory fan/clutch which are working as expected. I don't believe it is a condenser cooling issue, as I have the same result if I drive 60 mph, which should provide plenty of cooling air. Thanks for your reply, it is appreciated!
Al

 

Pressure on high side runs about 175 PSI at 80 degree F ambient temp. since this is a POA system, there is no "kick out" due to high pressure, it just gets released through the POA valve to maintain low side pressure. Any thoughts/ideas appreciated.
Al

 

134a high side pressures get really high. Just part of the game. The humidity/temp/discharge/pressure table is only for a point of reference. I find it mostly useful to know whether or not my discharge temp and low side pressure are in the ballpark. I don't find the high side pressure in that table to be useful.

I've started tracking superheat and subcool when charging odd systems. Best thing is to get the system running, get all the temps and pressures equalized, shoot in another 4oz. If high side pressure is going up and subcool is getting bigger, but outlet temps and low side aren't changing, then it's full. Probably.

Converting to a parallel flow condensor is a really good idea for 134a - and there are direct fit ones available now!!! - but not strictly necessary.

If you have a mostly stock system - A6 compressor, big muffler on the discharge line, stock or near-stock sized condensor - then I usually do ~50 oz of 134a. I expect you're still very undercharged.


My current system - with an R4, no mufflers, parallel flow condensor - takes about 32 oz.

 

Ok, I'll try to put more refrigerant in. what still concerns me is the by pass line, anyways frosty while the evaporator exhaust just cool, don't you find that odd? I'll let you know how things work out with additional R-34

 

Have you readjusted your POA valve to more like 28PSI? There are a lot of threads on how to do that, or you can buy one already set up for 134a from many suppliers.

 

It was in the original post:
And I gotta say, the continued use of R-34A is killing me. It's R-134A.

 

And somewhere back there I thought that I saw an R-34. All these refrigerants are confusing me.

 

I have adjusted it down from about 28 PSI. As I understand it, the higher the PSI the less cooling you have (higher low side PSI = higher back pressure) This is correct thinking for a POA A/C system, isn't it?

 

you are correct, sorry about the confusion.