Automotive Air Conditioning Information Forum

I have read a few posts here and can't seem to find one that is similar to my situation.

1983 Toyota Celica Supra, converted to 134a.
Recently got my A/C system up and running after many years sitting with no refrigerant in the system. Replaced all the o-rings. Noticed some gunk on the connections and inside the pipes. I cleaned them as best I could though I don't think I got all of the gunk off. Condenser is stock and meant for R-12. Compressor is for R134a after I swapped out the engine. Evaporator, dryer, EPR, expansion valve and all soft lines are new.
Vacuumed the system and it held vac over a multi day period. Held 90psi of pressure for a couple of days as well.
Charged the system with 24oz of 134a. Conversion chart of R12 (26oz) to R134a said I should only use 18-20oz of R134a.
When I charged close to 18oz the high side never really got above 175psi @65F or so and I decided to charge more until the high side reached closer to 250 @65F and that was when the charge bottle was empty. Also, when initially charging the system it took a few minutes, ~3min, to build any sort of pressure on the high side.

Now my current situation is:
Air out the vents is only slightly cool with fan speed on hi.
Ambient Temp~65F
With system off static press is about 55psi
System on engine idling at ~700rpm:
Low side pretty steady at 45-50psi
High side fan off will climb to ~250psi before the trinary switch kicks the fan on (Drier/HP side lines/condenser are hot to the touch) The pressure will steadily drop and the trinary switch kicks the fan off ~175psi (Drier/HP side lines/condenser are hot to the touch) and climb again to ~250psi. This is with only a 10" pusher fan. When my radiator fans (2 - 11" SPAL puller fans) kick on the pressure will drop down to equalize with the low side pressure (Drier/HP side lines/condenser are just warm to the touch). When the dual fans kick off it takes a few seconds (~10 to 20 sec) for the pressure to start to climb and start the whole cycle again as pressure climbs back to ~250psi when the condenser fan kicks on. Radiator fans cycle less frequently than condenser fan.
When the high side has pressure there is a large temperature difference at the evaporator lines. Low side is cold and high side is hot. This is the same at the compressor. Didn't feel the lines with the hi side at the lower pressure value.

Though all of my searching I cannot find anything that is related. The static pressure indicates proper pressure. The inability of to build pressure indicates a worn/bad compressor but since it still builds pressure it should be ok.
Any thoughts as to what the issue may be?
Using the typical charge charts they say Hi Side pressure should be such and such. Is this with the fan running or not?
Is the high side pressure fluctuation normal?
Does oil need to be added each time the system is placed under a vacuum? I put in 30oz (oops, meant 30cc) of PAG46 oil when I first charged it after holding a vacuum for a couple of days. 20cc were because of a new dryer.

Thank you.

Darrow wrote:Does oil need to be added each time the system is placed under a vacuum?

NO

Darrow wrote: I put in 30oz of PAG46 oil when I first charged it after holding a vacuum for a couple of days. 20 oz were because of a new dryer.

Wow, that's a @#$%^&*%$#@$&&$#@$^&^#@ sh*tload of oil !!!! Big issue.

Sorry not oz. 30cc

You mention an EPR valve. What pressure is the EPR calibrated to?

Where did you get the idea that you need 250 psi on the high side @ 65f ambient?

I am not sure what the value of the EPR is set to. Most likely a value that works with R12. I can't find any documentation on it.
I am looking at the charge chart for 134a and I miss read kPa for the PSI value. Should be close to 150 on high side. So the system is over charged?

Looking into the EPR valve. It looks like changing the setting on the spring takes a degree in HVAC that I don't have.
Is it possible to adjust the spring pressure to get it to work with R134a. I am assuming so since they do make them for 134a applications. Am I looking to reduce the spring pressure or increase the spring pressure? I am thinking what ever causes the EPR to open more is what I want to do. Is this correct?
Some reading on retrofitting older systems is to remove the EPR valve entirely and use a thermostatic switch to control the compressor. I can find a lot of thermostatic switches for home 120v ac systems but very few for a car application. Anyone have recommendations for a good thermostatic switch out there?
Thanks for the help.

Or, you could just leave it R12 like you should have.

Originally that car had a viscous clutch mechanical fan, that passed air over the condenser all the time. That sounds like it is missing.

Is the compressor new or rebuilt? Did it have any oil in it when delivered?

.

Viscous clutch fan is missing because the engine has been swapped. The new engine only has electric fans not option for a mechanical fan.
The compressor came with the engine. It was running and working when the project began a few years ago. The ports were blocked off at that time.
There is no noise coming from the compressor.

Well, you should have the condenser fan and one puller fan come up on the compressor clutch circuit. That will fix the condenser airflow issue.

Correct the charge level, that overcharge is not helping.

Is the new compressor close to the displacement of the original? Or is this an LS swap?

Mismatched system components can be a challenge.

Once you get the charge level corrected, you can do a full load test & record the pressures / ambient temperature / vent temperature

Cooling at idle near 700 rpm is near non existent. Kinda sorta feel some cooling but not much. When driving, so rpm is higher usually above 1500rpm, the air out of the vents is cool, not cold just cool. Higher the rpm the cooler the air gets to a point. Charge weight is what it should be when looking at the conversion from R12 to R134a. 26oz r12 to 20oz r134a. Could this mean I have a bad/weak compressor?

Compressors look about the same size but I cannot find displacement of the condensers.

For the pressures: Should they be measured with the fan on or off?
Should I always have one radiator fan on when the A/C is on and have the booster fan trigger when the pressure gets higher?