I attempted charging my AC system (1970 SS factory air converted to 134) and came up with a few more questions:

I connected a set of manifold gauges and vacuumed the system to over 29" for about 30 minutes after testing to make sure the system held a vacuum. My high pressure hose had an R12 fitting on it so I used a brass adapter that came with the gauges. I noticed the high side gauge never moved. Is this normal?

Next I charged with about 4 1/2 12 oz cans of R134 through the low side with the AC on high. I got a pressure of about 35 on the low side but the high side guage never moved. The AC temp at the vents felt cool but was only about 55 degrees.

Half way through I noticed the hgh side adapter was slightly loose. I tightened it and kept going.

I finished charging as the car began to overheat. I think it overheated due to a combination of defective fan clutch and hot condensor. The high side needle still never moved.

My questions are:

1. WHy did the high side gauge never move? Do I need a different adapter for the R12 fitting?

2. Would the overheating condition affect the ability to properly charge the system?

3. What ballpark pressure reading sshould I have gotten on the high and low sides?

4. Each can seemed to have a small amount of refrigerant left when I unhooked it. How long should each can take to empty into the system and should it empty entirely?

Thanks in advance, Kevin

1. Check your high side hose for a schrader valve in the end, maybe the adapter isn't depressing the plunger on the valve.

2.Yes, the overheating condition will effect the state of charge with R134.

3.The high side should be about 2.2 times the ambient air temperature, the low side should be in the mid 20's with R134, if you are using the stock system with a POA valve it probably won't go below 30ish.

4.There is always a small amount of pressure left in the can when I disconnect them.

Your system may be overcharged, I would not run it until you can get an accurate high side reading.

Yes I do have a schrader valve in the high side fitting and my adapter is not depressing that valve. I picked up an adapter that has a schrader valve in it. Should I remove the R12 schrader valve and screw on the adapter or do I leave the R12 schrader valve intact and screw the adapter right over it?

If I have to remove the R12 schrader this means I'll be letting the R134 out. Then I'll have to vacuum it down and recharge. Im sure some oil will come out in the process. How do I determine how much oil to add back?

Thanks, Kevin

Recover the R134 and remove the original Schrader valve cores on both the low and high side connections and reinstall the R134 adapters, reevacuate and recharge. I found that about 90% of what the R12 charge would have been works for R134a.

Thanks, Will I have to add oil after I reevacuate? Initially I put 11 oz into the compressor. Kevin

A couple of thoughts. It seeme to me, if memory serves me right , that the center piece of those brass adaptors can be adjusted for depth. I mean the part that would be depressing the schrader valve stem. I have had to both adjust or replace them in the past to get them to properly depress Schrader valve stems. They screw in or out just like the Schrader valve and I think you can use the same tool(tire valve tool). You should be able to buy them at your local auto store if you are missing one.

Obviously this would also be true of your manifold gauge set. Any missing parts there would also cause you to have no hi side reading.

Hope that helps! smile.gif

Thanks guys