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Fixing an old R12 System

rmmagow on Fri April 25, 2008 4:23 PM User is offline

Year: 1989
Make: Mazda
Model: 929
Engine Size: 3.0
Refrigerant Type: R12
Country of Origin: United States

I'm going to try to fix the A/C on my old Mazda 929. The R12 refrigerant mostly leaked out due to the car having to sit for nearly a year waiting for other work. Prior to the sitting the A/C was bone-crushing cold. I do have my 609 certificate and have been able to source 5 small cans of R12. I have a manifold set too, but that is about it. I will be buying a Vacuum pump from here as well as whatever comes out of this for a leak detection kit. I did not open the system and the A/C compressor still spins freely (electrically disconnected for now).
My questions. Where do I begin to look for leaking? The A/C compressor has a lot of oily looking deposits on top as if the lines leading in might be leaking. How would I use a leak detection dye or kit? Do I need to put a charge into the system first? I did put some r12 in and the A/C started working but quit after a couple of days. From sitting, where is the system most likely to have developed a leak? A/C compressor seals? Receiver/Dryer? Should I just go through and replace all the o-rings I can find or spend my time looking for the leak and leave well enough alone? How tight do I make the connections when replacing the o-rings, spark-plug tight, lug-nut tight other? Do vacuum pumps just hook up to the charging hose on the manifold gauges? Since I'm only taking care of my personal vehicles and time doesn't matter would a small vacuum pump be OK, like a 1.5 or 3 CFM?
I don't want to do 134a in this car and no-one will do r12. The system actually still has pressure in it so it can't be too bad a leak. If A/C kits people see this maybe you can build me a list of things to order to get started, I'll contact you anyway once I get going. This car has a pretty nice basic A/C system. I have another 89 929 and it's nice and cold even at 90 +.

Thanks Very Much

mk378 on Fri April 25, 2008 4:39 PM User is offline

While you still have pressure you can check for leaks with a sniffer. It's apparently a pretty big leak. I think that compressor has 2 case seals and an oil plug that could be leaking and putting oil near the back.

rmmagow on Fri April 25, 2008 9:51 PM User is offline

Actually whatever pressure is left has been in there for a long time, at least the past 6 or 8 months. So I'm thinking it's a leak sensitive to high pressure but once the pressure drops low enough it stops. There's a low pressure switch on the receiver dryer which I jumpered for a minute and the compressor then kicks in and turns without a lot of noise. I may just dump in a can of r12 and dye and see what I can see. If the compressor seals leak should I bother with rebuilt or just go new? Will r12 sealant fix a compressor leak or it that stuff mainly meant for small holes. I'm not real hot to use the crap anyway.
Thanks for the reply.

NickD on Sat April 26, 2008 8:30 AM User is offline

Do you have positive pressure? All MVAC systems leak and less than one ounce per year is considered very good, we are talking about 19 years here so do the math. Odds are in your favor if you still have positive pressure, your leak is very small and it just may need topped off, but stuff happens. My 88 Supra still has the original charge in it, well knock on wood, another spring and I didn't check it yet this year, still too cold. Japanese did a very good job in the 80's, yeah, they have gone to hell like everyone else.

If you have positive pressure, can risk a can of R-12 and find out, just run your engine at 2,000 rpm, AC on, 80*F day or above, blower at max, doors open and top it off observing the sight glass to see if that foam goes away, leave some bubbles in the glass and watch it, if after a couple of week the amount of bubbles does not increase, you are okay.

mk378 on Sat April 26, 2008 9:18 PM User is offline

Once the switch cuts out (at about 50 psi) there is only a few oz of refrigerant left. There is no liquid refrigerant at all. If you charged once and lost it in a few days it is essential to spend some time finding the leak.

Use UV dye, not the red dye that is found in some old cans of R-12 with dye (If you have one of those cans, you can still use the R-12 out of it by holding the can right side up so the red dye stays in the bottom of the can.) Dye of any sort will only leak out while the system is fully charged and running. That's because the oil carries the dye. When stopped, the oil sits still and only clear gas refrigerant will escape from leaks.

If you're going to fully charge the system with R-12 to look for leaks, you need to have access to a recovery machine so you can remove the R-12 while making repairs and then reuse it.

Leak sealant is worse than useless. Never use it. It very rarely seals leaks. Far more often it hardens in the wrong place and causes major problems. The whole system (every part that carries refrigerant) needs to be replaced to get rid of it.

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