My 90 Ranger developed an audible leak in the compressor discharge
hose (currently holding 65 psi wrapped with electrical tape). It's a
R-12 system. Now, when I pressurize the high side to 65 psi and
pull the low side to 26 inches of vacuum, the system stays that
way for hours. Would this indicate that the expansion valve is clogged
or could anything else cause this? Also, if I reverse the pressure
(high-side vacuum and low-side pressure) the low side loses pressure
slowly but the high-side holds its vacuum. The low side takes a while
to pressurize (more volume) while the high-side pressurizes quickly.

I had previously charged the system with R-134 cans with a U/V dye to
try to find the leak. Didn't need the dye, my ears found it. Could the
dye have clogged the valve? Or could the valve have been previously
clogged and that caused the high-side hose to leak?

If I replace the valve, is the special tool readily available? Or could I
just slot a metal tube and use that, and if so, does anyone know what
size tube/slot I would need?

 

I just tried one more thing. I shorted the pressure switch plug and ran the compreesor
for about 30 seconds. While running, the high side didn't budge from the 65 psi
previously charged and the low-side increased to 30 inches of vacuum. When shut off
the high-side still sits at 65 psi and the low-side dropped to 25 inches vacuum. Does
this indicate a possible compressor problem?

Also, if the vacuum holds for what looks like will be forever, does this indicate that
there is little to none water in the system (since evaporation would reduce the
vacuum)? I've got a new accumulator/drier so I'll replace it anyway but I wonder
if this was necessary.

 

I'm having trouble following all the low/high side stuff, but I think I get the jist of it (thread title). Here's what I would do:

1) Remove the orifice tube (I doubt it uses an exp valve) and check for blockage. But more importantly, look for signs of debris that would indicate a mechanical problem with the compressor. If no debris replace with a new orifice tube. They are dirt cheap. There is a different color tube for use with R12 and R134. If there is debris from a compressor failure, times get tough. You will have to thoroughly flush the system, replace the compressor, then prey that every speck of dirt is removed. The opening in the orifice tube is measured in thousandths of an inch; it doesn't take much of anything to plug it.

2) Repair the failed high side hose.

3) Replace the accumulator/dryer since they are also a filter.

4) Evacuate with a vacuum pump and, after pulling vacuum (about 29 inches on the gauge) watch the gauge for 30+ minutes for evidence of a leak.

5) Charge the system. If you have access to nitrogen you can pressurize the system with this and check for leaks. If it passes, evacuate again then charge with refrigerant.

Your compressor probably has a high pressure cutout to prevent blown hoses; you can see this by looking for the wiring on the compressor. On dye, that crap has a spotted history of clogging systems; I won't use it myself. I like soapy water instead, and if push comes to shove I'll borrow a sniffer from a buddy. One way to reduce the odds of a leak are to simply replace the o-rings when you have the system open. They are really cheap to buy. Since it sounds like you're doing a R12 to R134 conversion, address the orifice tube change as noted earlier, then look at the oil charge in a R134 conversion kit. You can buy the kit if you like, or instead buy the oil charge and required R134 individually. The correct oil is needed because a R134 molecule is smaller than a R12 molecule; the oil used with R12 (mineral oil) doesn't provide a good seal on the compressor shaft and may/will slowly leak.

*I think the biggest factor in determining the sequence of events for repair on this one will be determining if there is a mechanical probelm with the compressor and if the system is full of crud.

 

This is one for the books: the high-side schrader valve was bad. It was
dpressed but blocked solid, so my manifold was showing the pressure in
its own hose and not the A/C system.

I removed the threaded end of the liquid line from the evaporator and
removed the orifice tube, no tools needed to remove it; it sticks out
about 1/8" so I just used my fingers. There were a couple of small black
flakes on it and a silver sliver the size of a coase hair about 1/8" long but
otherwise it looked fine. At that point I though I was screwed with a blocked
condenser.
In trying to remove the spring connector end of the hose from the condenser
I just couldn't get it off. The spring appeared to be pushed back into the
housing. I went out and bought every removal tool I could find but still no
luck. It looked like the spring was riding up on the flange because I could
see part of the flange in front of the spring. Turns out it was the entire
flange. Some monkey hadn't gotten the spring over the flange so the only
thing holding that end of the hose on was friction. I guess it was too small
a diameter to build up enough force to blow the hose off. I ended up just
walking it out by hand with no tools. Everything looked clean so I pushed
the hose back over the o-rings and removed the hose from the other side
of the condenser with no trouble. Then I pressurized the accumulator and
got air flowing from both the the loose hose and the condenser.

So no apparent blockage anywhere, What's the deal? I tried pressuring
the loose hose and the guage showed 65 psi but nothing came out of the
hose. That led me to the schrader valve.

So at this point, I'll be replacing the compressor output hose, the liquid
hose, the accumulator and the orifice tube. All the new hoses sold today
are barrier type and everything comes with R-134a compatible o-rings.
I guess I could drain the compressor oil and switch over but I've got 8
cans of R-12 and a quart of mineral oil so I'm leaning toward just putting
everything back together and sticking with R-12.

Thanks for your help.