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Re-Charging an 89 Mazda 929

rmmagow on Tue May 20, 2008 1:12 PM User is offline

Year: 1989
Make: Mazda
Model: 929
Engine Size: 3.0
Refrigerant Type: R-12
Country of Origin: United States

Going to rescue the A/C in my old 929 and stay with R-12. I am planning to buy big-blue for leak detection, new washers/gaskets and Nylog lubricant for the washers and gaskets. Which Nylog - the CFC right? There is still some pressure in the system. My initial plan is to introduce enough r-12 to activate the low pressure switch that's located on the receiver/drier assembly, use the big-blue to see what I can find for leaks and fix 'em. I'll have the system professionally evacuated, fix the leaking areas, have it evacuated again. I've got a 609 so I can buy R-12 and I have a full set of charging manifolds. I'll recharge partially, leak test again and assuming all's fine charge the system thoroughly via the shop manual.
The system worked fine for 17 years but seems to have lost most of its charge due to sitting for a year. Based on "oiliness" I think the leak is where the system attaches to the compressor.
Question, how tight does one make the hose to hose connections, the hose to compressor connections? Lug-nut tight, spark-plug tight?
If big-blue doesn't indicate any significant leaks is it OK just to re-charge to factory specs without an evacuation?
Thanks Very Much.

94RX-7 on Tue May 20, 2008 5:03 PM User is offline

You should strongly consider replacing the dryer while you have the system open since it has 19 years worth of moisture in it. I would also encourage you to just go ahead and replace all the o-rings in the system since, again, they're 19 years old. As far as fitting tightness goes, it doesn't take a lot since there's an o-ring that's actually making the seal. You just need enough tightness to squish the o-ring down into place good. I looked in my RX-7 shop manuals (yes, I know, different car) and they indicated somewhere around 11-14 ft-lbs. Your shop manual doesn't have fitting torque information?

mk378 on Wed May 21, 2008 10:32 AM User is offline

The pressure not being enough to close the switch means there is almost no refrigerant left. Rather than put more R-12 into a leaky system, I suggest you start by recovering what remains and then temporarily put in some nitrogen or R-134a for "static" (compressor not running) leak testing. Do not run the compressor without a full charge of R-12. Do not exceed 150 psi with nitrogen or other non-condensible gas, the evaporator may burst. The big advantage of using R-134a for leak testing is it can be detected with an electronic leak detector.

The o-ring makes the seal. When you have a leaky fitting you'll have to take it apart and replace the o-ring, overtightening it will not help. The nut or bolt only has to be tight enough to bring the metal parts together and not vibrate loose. The o-rings on fittings between the compressor and condenser are more prone to harden and leak because that line runs hotter than any of the others.

Definitely put on a new drier. If you're going to put R-134a in for leak testing you should put a new drier on first because the old one may not be compatible.

If your car has a serpentine type condenser it's a pretty good candidate for conversion to R-134a.

Oil on the outside of the compressor could be coming from leaks at the compressor case seals and relief valve too.

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