Stick with R12 or do the R134a conversion?

pete_89t2 on Sun July 10, 2011 4:51 PM

Year: 1989
Make: Mazda
Model: RX-7 Turbo
Engine Size: 1.3BT
Refrigerant Type: R12
Ambient Temp: 85*F
Pressure Low: 6 psig
Pressure High: 100 psig
Country of Origin: Japan

Hi, 1st post from a new member, hoping to get some good advice here. I've got an '89 Mazda RX-7 Turbo that recently started having an A/C problem. With the A/C on max, the air blowing out the vents is barely any cooler than ambient temp. I've owned this car for about 13 years; since 2004 it's been strictly a weekend car/track toy that I don't drive every day, and the A/C has always blown out ice cold air whenever called upon since the day I purchased it. FYI, the A/C unit is the factory stock Nippon Denso compressor, and it has never needed a recharge or had its A/C opened up or serviced in any way since I've owned it. Also FYI, I'm not an A/C tech, but am an experienced shade tree mechanic with several engine rebuilds & car restorations of all sorts under my belt. So the first thing I did was a thorough visual inspection of the A/C system for any oily spots that could be signs of refrigerant leakage, and found none. FWIW, I have always kept my engine bay extremely clean which make spotting any stains & oily spots pretty easy. Also, the compressor clutch engages properly, and the compressor operates without any abnormal noises.

Then I consulted with the Mazda shop manual (FSM), and picked up a loaner manifold & gauge set from my local auto parts guy. Since the loaner gauge set is designed for R134 fittings, I also had to purchase the adapter R134 to R12 fittings and installed them on my car's low & high side service ports. Then I proceeded to take some pressure readings, ambient temp was 85*F per my garage wall thermometer where I did the work. First I took a static reading (engine & A/C not running) to ensure the gauge set wasn't going to leak and to get myself a baseline; results were an equal at 84 psig on both Low & High sides. The Mazda FSM doesn't tell you to do a static test, so I have no idea if these readings are normal?

Per the Mazda FSM, I took the next readings with the engine running & warmed up to operating temp, A/C on and set to MAX, at a 1500RPM high idle. Readings were 6 psig Low side, 100 psig High side. While testing, the compressor clutch was constantly engaged (no cycling) and compressor ran & sounded normal. The FSM states that if readings are
I guess my 1st question is given these readings, how do I interpret them? They meet the low side criteria, but my high side is a bit lower than the range the FSM states - is that due to testing at a different temperature (85 vs. 77F)? Is this indicative of a 22 year old car who's R12 just fizzled out enough to not work properly, or its it more likely that I have a leak somewhere?

Most of the shops doing A/C work in my area are R134 only, meaning I have no choice but to do the conversion. However I'm leery shops that push conversions when no two shops seem to do the conversion the same way when I press them for details. I did find one shop that said he can recover my remaining R12, vacuum the system down & test for leaks, fix any if found, then evacuate and recharge it back to specs with R12/oil charge, hopefully most of it being my recycled stuff so I'll only need to buy a can or 2 of new R12. He also recommends replacing the receiver/dryer given the age of what's in there now.

I'm leaning towards going the R12 route - taking a gamble that if a leak is found it won't be of the expensive type to fix, and once done I should get many more years of service from my A/C. Do you guys agree? If the conversion route makes more sense, can you advise what needs to be done to do it right? I hate doing half-a$$ed jobs, and I've read too much conflicting information on this subject to know what the truth is!

Thanks in advance,
Pete

TRB on Sun July 10, 2011 5:40 PM

In the US if you get certified ($25.99 dollar test) you can buy R12.

Sounds like you have a small leak or even after 20 plus years, you have leaked down a little. An a/c system can do this over time. It's still holding some refrigerant. So I would imagine a simple repair, evacuate and charge back to R12 would provide the best cooling.

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Contact: ACKits.com

mk378 on Sun July 10, 2011 6:44 PM

When was the last time that it worked properly? You've gone from a full charge to practically nothing in that time interval. It seems like a fairly major leak has just opened up, so you should definitely find it rather than just regas and hope.

bohica2xo on Sun July 10, 2011 7:32 PM

Stay with R12. Do not convert that system.

Recover it, add back an ounce of oil mixed with dye, and charge it to spec. If it loses the charge by next summer, go hunting with the black light.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

pete_89t2 on Sun July 10, 2011 7:43 PM

Quote
Originally posted by: mk378
When was the last time that it worked properly? You've gone from a full charge to practically nothing in that time interval. It seems like a fairly major leak has just opened up, so you should definitely find it rather than just regas and hope.

Well, the lack of cooling first became very noticeable in the last few weeks, with temps here up in the 90's. Like I said, this car is a weekend/track toy so I don't drive it every day, but each year I do take it to a car club gathering at Deals Gap TN, which puts a little over 2000 miles on it round trip over the course of a long weekend. That trip was back in April/May, and this year on the way home it was unseasonably hot, and I noticed the A/C seemed a little strained. It cooled the cabin OK, but seemed to take a bit longer than usual to cool things down - I just assumed it was due to it being unusually hot that day, but maybe it's been slowly leaking down since then?

I suppose it could have a major leak, but wouldn't the static pressure measured be much less than 84 psig if it was completely blown out?

Dougflas on Sun July 10, 2011 8:40 PM

Just add R12 with dye. Add a small amount of R12 at a time. Get the temps up and pressures close. I would not open the system at this time. It still has refrigerant in it; just not enough. I would not convert to R134. I wish you didn't put 134 adaptors on a R12 system. MAKE SURE VEHICLE IN MARKED R12

pete_89t2 on Sun July 10, 2011 10:27 PM

Quote
Originally posted by: Dougflas
Just add R12 with dye. Add a small amount of R12 at a time. Get the temps up and pressures close. I would not open the system at this time. It still has refrigerant in it; just not enough. I would not convert to R134. I wish you didn't put 134 adaptors on a R12 system. MAKE SURE VEHICLE IN MARKED R12

The adapters were a temporary install so I could use that 134 only gauge set; I installed the R134 adapters without any thread lock compound, just a little teflon thread sealer. When I was done I just unscrewed the adapters, cleaned the teflon residue off the R12 fittings and it's back to stock.

Thanks for the advice guys!