I decided to get back to work on the AC project.
Here is my to do list:
- Adjust POA valve
- Flush evaporator and POA valve
- Install o-rings throughout
- Install hi pressure switch
- Add PAG oil
- Wire compressor and fan relay
- Install compressor belt
- Evacuate and charge
Starting with the POA valve, I recently picked up the 1970 chassis service manual which has all kinds of great info on how the AC system works as well as diagnostics and repair. Per the service manual, the valve setpoint from the factory was 29.5psig at sea level and that appears to be where mine was adjusted. To get roughly the same evaporator temperature from R134a as I would have had with R12, I would need to adjust the POA down to about 27psig, however after a little discussion and reading up here on the auto ac forum I've decided to target a lower pressure of 26psig. This will give a freon temperature of about -1C or 30F which is technically below the freezing point of water, but with warmer air flowing over the evaporator it's still very unlikely to ice up and should give better cooling performance.
Here is a video explaining the POA adjustment. I used a 3/8" socket to loosen the lock nut and a 7/32" socket to adjust the setscrew.
It was really hard to see the gauge or line up the camera phone while taking video, so I went back and snapped a photo to show it indeed was set at 26psi.
Satisfied with the POA adjustment, I took it off the system and got setup to flush the evaporator. Flushing removes any residuals of the old lubricant and R12 residuals that may not play well with the new R134a, as well as cleans out any debris that may have accumulated while the system has been unsealed for the last twenty years. I used an aerosol flush called A/C Pro "Power Clean and Flush". Below is a photo showing how I set it up. The flush is fed into the outlet of the evaporator and I used clear poly tubing at the evaporator inlet to a plastic container under the car. That allowed me to monitor the color/cleanliness of fluid coming out. Once I ran all the flush through, I blew it out with compressed air.
Below is a video showing some of the process. When I went to air blow the system, some of the flush was forced out of the small oil bypass line so I added another tube to route that down to my collection container. The function of the oil bypass line is to make sure oil in the system is always allowed to circulate back to the compressor even if the POA valve is mostly closed.
Here is my collection container showing the amount of flush that went through the system and the resulting color. The amber color of the fluid is mostly from the first few seconds of flushing when the flush came out pretty dark.
Not photographed, I also flushed the POA valve on the bench into a bucket.
Can anyone advise me on what amount of compressor oil to put into this system?
Since it has all custom hoses, a 14"x24" parallel flow condenser, and a different compressor (Denso 10S17) from the factory system, I'm not sure if the factory oil amount is appropriate. The compressor is used but the oil has been drained from it. The evaporator and the POA valve are original to the car. The drier, condenser, TXV, and hoses are all new.