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Pressurize AC System to check for Leaks?

RandyJ on Sat June 30, 2012 10:32 AM User is offline

Year: 89
Make: GMC
Model: Sierra
Engine Size: 350
Refrigerant Type: R134a
Ambient Temp: 99
Pressure Low: 0
Pressure High: 0
Country of Origin: United States

I just put a retro kit on my 89 GMC. The AC has been blowing warm air for a couple years due to a small leak and no freon was left in the system. I pulled a vacuum but after 30 minutes, I could see it had a leak since it wasn't holding the vacuum. It is a small leak.

Can I pressurize the system with air from an air compressor then check all the fittings/connections with soapy water and look for bubbles or will this harm the system? I have read on other forum that people have pressurized with nitrogen to perform this procedure but I don't have those resources but I do have an air compressor. Anybody ever done that before?

iceman2555 on Sat June 30, 2012 12:12 PM User is offlineView users profile

Why not simply add a bit of 134a to the system and test for leaks. Air will not always indicate a leak....molecules are larger.....use refrigerant....a few oz should produce sufficient pressures to enable leak testing....if a good leak detector is used...soap bubbles is not an acceptable method....old time procedure than may not reveal leaks....the leak could be so slight that air escaping would on result in a positive test.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

RandyJ on Sat June 30, 2012 2:40 PM User is offline

RandyJ on Sat June 30, 2012 2:58 PM User is offline

I figured if it was drawing air in (under vacuum) then it will certainly blow air out (under pressure). I realize that there are a whole lot of better options and fancy equipment out there that can do the job but I don't have any of that. My budget is limited and I can't spring a few hundred dollars for a leak detector that I will probably only use one time.

I am trying to accomplish this using the resources I have available if possible. The soap bubble method may be old school but if it works then that is all I am looking for. My main concern is: Will pressurizing the system with air from a standard garage air compressor ruin or damage the system? If it will, then I won't do it. If it won't then I'm going to try it first. I do have a great 2 stage vacuum pump and can pull a vacuum down and hold it down for as long as I want to in order to pull all the air back out.

mk378 on Sat June 30, 2012 4:41 PM User is offline

Use R-134a like Iceman said. It only takes a couple of oz. If you have any sort of TIG welding gas (CO2//helium/argon or either one alone) that can be used as an inert gas similar to nitrogen. Do NOT use oxygen or acetylene! Use a regulator on any high pressure gas bottle.

In the summertime when you open an air hose, actual drops of water will often come out. You do not want that in your system.

It should also be noted that the conversion kit in a box ("death kit") is not a proper conversion. And that the late 80's 1500 GM trucks do not convert well.

Edited: Sat June 30, 2012 at 4:43 PM by mk378

jglanham on Sat June 30, 2012 5:06 PM User is offline

Why not buy a can of 134a that has UV dye in it? Most auto parts stores have inexpensive UV flashlights (the led type). If the flashlight isn't strong enough to see in daylight, wait until
nighttime. Keep in mind that you probably won't be able to see a leak in the evaporator unless the system is charged enough for condensation to drip on the floor. The condensation will show green if the evaporator is leaking. Good luck!


RandyJ on Sat June 30, 2012 8:01 PM User is offline

Thanks for the replies. Looks like 12oz can of 134 with the uv dye and a uv light kit is the way to go. That's what I am going to do.

mk378 on Sat June 30, 2012 9:56 PM User is offline

Dye really only works with the system fully charged and running -- it needs to circulate with the oil. When not running the refrigerant tends to escape as clear gas.

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