Air compressor to r12/134 fitting


Staff member
Dec 14, 2002
New Jersey
Trying to sort out a car that I can’t tell if it has a badly leaking evaporator or a bad joint someplace.

I pulled a hard vacuum but it wouldn’t hold.

I tried some es-12a refrigerant. Normal process should be bone dry nitrogen laced with r-22 and to use a sniffer. I don’t have that gas mix and am not interested in procuring it. I installed the es-12a (8oz) and it got to a low pressure that kicked the compressor on, then after a short time the pressure was gone. When running a high side leak occurred at the coupler. I can’t tell if it was the actual 134a female coupler not being on tight, or something else. I don’t want to try yet with another can of es-12a.

When I sniffed with a combustible gas detector I got a good result at the high side fitting, a minor result at a threaded joint on the low pressure hose, and a result at the evaporator box. I have no reason to think the evaporator is leak free, but I don’t have reason to believe it is all in the evaporator. No combustible gas or smell in the cabin, which I would assume would be present if the evaporator was leaking.

Anyway, I’m not concerned about moisture in the system, so I’d like to diagnose with 90psi shop air (static system, will NOT turn on ac compressor) to scout for leaks especially at the high side coupler.

I think I need an NPT to 1/2” acme thread but I’m not sure. Can anyone recommend what I need to couple my gauges to an air compressor line? I could cut a refrigerant line and install a barb fitting, but I figure there must be a better way.

With a big leak, do a static test. Admit a small amount of the test gas, literally just enough to move the needle on the gauge, and sniff for it. It is fine to use HC gas with a flammable gas detector. It is also legal to use a few oz of straight R-134a and a refrigerant detector for leak detection. Do not run the engine. If you use a lot of test gas you'll just fill up the garage and cause false alarms everywhere.

Everyone thinks that their shrader valves are the leak but that's usually not the main problem. There's always traces of refrigerant around when you take the coupler off.
Look for refrigerant oil-it will usually come out with the leaking refrigerant. Look closely at hoses, compressor clutch, etc., you’ll usually see it. Unless you’re unlucky like me & the evaporator is leaking! It’s OK to add a couple ounces of refrigerant & pump it up with nitrogen, poke around with the leak detector. Refrigerant is heavier than air, wave the wand underneath all connections. And under the evaporator condensate outlet…:rolleyes:
Put dye in the system-it's available at almost any parts store. You can get it with the light that highlights it or get it separate for around $10.

Turns out HD has a flare to NPT fitting. So this should work…

Also, I wouldn’t use shop compressed air to leak test-both the compressor oil vapor & moisture are bad for an A/C or refrigeration system.

The receiver dryer is going to have to be replaced regardless. I’m going to troubleshoot with ES-12a (propane/butane), which don’t care about moisture.

It’s going to be a long time and much flushing before the system ever sees 134a, if it ever does.
I also made my own air compressor piece for testing purposes. Yeah I ran my AC on like that for less than a minute just to make sure that it otherwise worked.
So, I think my high side adapter is suspect. Or else the way it seals to the OE high side port.

Like yesterday when applying es-12a, as I pressurized the system with compressed air, it started to leak. There is still a lot of oil and dye there from yesterday.


As I pressurized the system it started to leak fast and loud. Even after I adjusted it, there was a bit of seepage until I got it “just right”.

I filled it to ~90, and will check again in a while.


If it holds 90 overnight then I’ll test with more dye, oil, and Es-12a. I’ll be relieved if I find that it was just the hose blowoff and a bad seal.
It didn’t hold at 90 after I removed the gauges. I still think the quick connects are suspect. More investigation when I have time…
No luck finding it. I tried air, and also tried more ES-12a. Even if the ports are suspect, I smell the refrigeration oil smell after running the system a while with Ed-12a then shutting down. The charge is lost fast after shutdown.

The one thing I kept running into that I thought was odd was that while pressures were always ok, the high side adapter would keep popping off and leaking refrigerant out.

These cars are known to leak from the evaporator and I suspect that’s it.