AC Positive Pressure test to find leaks?

[BlueTankRanger97]

I have a 97, 4.0 4x4 and the AC Sye=stem is empty. I would love to find the leak myself so I have a better understanding of what repairs need to be made. I have a set of AC gauges, a vacuum pump. When I put a vacuum on it it looses it in seconds. I do not want to invest in a N2 system so I am curious about using shop air. I would like to find a fitting that allows me to connect a shop air hose to the yellow hose so I can spend some time with a stethoscope and soapy water to find my leak(s). I suspect the fitting to the compressor. I pray it is not the exchanger in the dash. Is there a way to assemble an air hose fitting to the vacuum hose on the gauges set. I know the dryer needs replacing. I know the clutch works, but with NO freon in the system it is a bitch to find the cause. Thanks in advance.

 

[franklin2]

It's not recommended, but I have done it 3 different times on different systems with no ill affects.

I never throw anything away, and I had some old r134a cans that have the built in hose, gauge and 134a fitting on the end. I took and cut the hose near the empty can, put a barb 1/4 fitting on it with a hose clamp, and then screwed in the air quick connect fitting that I use in my shop (the common Harbor freight quick connect). I then put what my shop compressor has on it, about 125 psi on the system. Works great, if you have that large of a leak you can usually hear it.

When you are done and get it sealed up, I usually hook the vacuum pump up and let it run most of the day. Besides pulling the air out, you are boiling the moisture out of the system. Water will boil at room temperature if you put a vacuum on it. So you let it sit there and let any moisture that you introduced with the shop air get turned into a vapor and pulled out with the pump.

 

[19Walt93]

Why not just charge it up with some dye and check for leaks after you run it for a while? It sounds like your leak is bad enough to produce a stain in just minutes.

 

[lil_Blue_Ford]

So, I muddled over this problem for a bit. I didn’t really want to use shop air because of moisture concerns but I do have a couple tanks of CO2 for welding and home brewing so I just used one of those. They are standard JIC/AN type fittings same as the gauge set uses on the regulator setups so I was able to just screw it on the gauges where the yellow hose is and put 40 psi into the system. Sprayed everything down with soapy water and found the leak from the center seam in the pump.

 

[superj]

i use shop air and than the pump to burn the moisture off. but i also run propane in my older ac systems too which has some moisture in it too.

 

[BlueTankRanger97]

It's not recommended, but I have done it 3 different times on different systems with no ill affects.

I never throw anything away, and I had some old r134a cans that have the built in hose, gauge and 134a fitting on the end. I took and cut the hose near the empty can, put a barb 1/4 fitting on it with a hose clamp, and then screwed in the air quick connect fitting that I use in my shop (the common Harbor freight quick connect). I then put what my shop compressor has on it, about 125 psi on the system. Works great, if you have that large of a leak you can usually hear it.

When you are done and get it sealed up, I usually hook the vacuum pump up and let it run most of the day. Besides pulling the air out, you are boiling the moisture out of the system. Water will boil at room temperature if you put a vacuum on it. So you let it sit there and let any moisture that you introduced with the shop air get turned into a vapor and pulled out with the pump.

Actually it is kind of recommended in my case. Shop air on a completely dead freon free system is cost effective, safe for the environment, which I really am not interested in getting into a "global Warming" debate, cuz it is all BS, and repeatable. Seeing as how I KNOW i have a leak somewhere and will need at least new rings, a Complete and serious flush and a new accumulator as well as a new O Tube, More than likely a new compressor also, it makes sense to use shop air. I only wish I had kept a recharging can and hose from a while back use on another car. Saving that hose is genius!

 

[BlueTankRanger97]

So, I muddled over this problem for a bit. I didn’t really want to use shop air because of moisture concerns but I do have a couple tanks of CO2 for welding and home brewing so I just used one of those. They are standard JIC/AN type fittings same as the gauge set uses on the regulator setups so I was able to just screw it on the gauges where the yellow hose is and put 40 psi into the system. Sprayed everything down with soapy water and found the leak from the center seam in the pump.

I too have a couple of CO2 bottles from the same type of endeavor. As stated above in a previous reply, I will probably go the shop air route since the system is completely empty and a leak is obvious. Just not sure where. I am suspecting the hose manifold tie-in on the back of the compressor. Since it is contaminated anyway i am gonna try the shop air route and not waste my small bottle of CO2. Shop air is cost effective and repeatable. Also since there is NO freon, oil or dye in the system I will want to try with higher pressure to really make is sing. I just hope it is where I suspect and NOT the evaporator. Rear of the compressor is dirty so I am suspecting that manifold is leaking. Thinking I can steal some fittings off the CO2 stuff..... good idea.

 

[BlueTankRanger97]

Why not just charge it up with some dye and check for leaks after you run it for a while? It sounds like your leak is bad enough to produce a stain in just minutes.

How do I "Charge it up" with dye if the system has absolutely nothing in it at all. ZERO static pressure on the gauges. Clutch does trip with 12 volts applied. Charging it up with freon is a big waste of money, not to mention pisses off the treehuggers in the group.

 

[pjtoledo]

speaking strictly of charging it up, the entire system will pressurize equally. the pump just puts more pressure on one side of it.

 

[lil_Blue_Ford]

I too have a couple of CO2 bottles from the same type of endeavor. As stated above in a previous reply, I will probably go the shop air route since the system is completely empty and a leak is obvious. Just not sure where. I am suspecting the hose manifold tie-in on the back of the compressor. Since it is contaminated anyway i am gonna try the shop air route and not waste my small bottle of CO2. Shop air is cost effective and repeatable. Also since there is NO freon, oil or dye in the system I will want to try with higher pressure to really make is sing. I just hope it is where I suspect and NOT the evaporator. Rear of the compressor is dirty so I am suspecting that manifold is leaking. Thinking I can steal some fittings off the CO2 stuff..... good idea.

So, in my case I had new everything except the pump. I hoped it was an o-ring. I wasn’t worried about spending the little bit in CO2.

Also, the low side of the system is supposed to be in the 25-50 psi range typically. So blowing it up to 100 psi with shop air is arguably not wise.

 

[alwaysFlOoReD]

I know next to nothing about AC, but isn't the low side and high side seperated by the pump and a small oriface? So if the pump isn't turning both sides would equalize thru that small oriface? In that case I don't think pressure up to the high side limit would hurt...

 

[Uncle Gump]

When it's 90 degrees ambient... 134a will show over 100lbs pressure

 

[Uncle Gump]

When the system is sitting static... pressure is equalized on both sides.

 

[BlueTankRanger97]

So, in my case I had new everything except the pump. I hoped it was an o-ring. I wasn’t worried about spending the little bit in CO2.

Also, the low side of the system is supposed to be in the 25-50 psi range typically. So blowing it up to 100 psi with shop air is arguably not wise.

The 25-50 psi is not quite true, from what i am finding in my research. Static pressure alone should be in-line with ambient temp and close to equal on both sides, high and low side as it will equalize when the system is off or static. In my case i have zero across the board. So I know i have a bad leak(s). just gotta find em. The system is capable of taking a lot higher pressure on both sides that 25-50 psi. IF i have a weak part and I blow it out at 100 psi, then I would love to find it now when I need to re-do the system rather than wait a few weeks and have to do it all again.... just sayin'. So mild stress testing sounds like a smart thing to me.

 

[BlueTankRanger97]

speaking strictly of charging it up, the entire system will pressurize equally. the pump just puts more pressure on one side of it.

That part I understand. But if I have a leaking system that has evacuated itself and NO idea where it is leaking from, how else can i "Charge up" the system to find the leak(s)?