Michael Benno

The PO converted my 1988 928 S4 AC system from R12 to 134a back in 2006 or somewhere there abouts. I don't think the O rings were replaced.

I had to top off my 134a after about 1 year of ownership. The levels drops just enough to trip the low pressure cutoff. Both times I had it filled, no leaks were detected.

My understanding is that 134a molecules are smaller than R12 and thus will weep out via the R12 spec O rings and that a proper conversion would require new green O rings to prevent leaking. Do I have that correct?

The top off service is about $100-$150. So do I just top it off periodically or go for the O ring DIY job I saw posted on the forum?

Thoughts?

upstate bob

just buy one of the cans with the hose and gauge attached. most auto stores and Big Lots has them.

Eplebnista

My thoughts:

1. Stop paying someone else to top it off. Buy a gauge set and learn how to do it yourself. You could say our cars came standard with AC. You could also say our cars came standard with a refrigerant dispersion system that sometimes also provides a cabin cooling function. This is particularly true if you have rear air. Having to top the system off every year, or every other year, is not that unusual even if you have all the right parts in the system. See if you can hook up with some other PAC NW shark folks if you want help learning how. It ain't rocket surgery.

2. The molecular volume of your refrigerant is likely to be much less of a factor than the 1988 vintage o-rings regardless whether they are black or green. The o-rings should have been changed when the PO switched to 134 as well as the receiver/drier. You may want to seriously consider changing them out now.

Good luck.

Imo000

It's a sealed system, regardless if you have R12, R134 or Propane in it. If the pressure drops and you need to top it off, you have a leak. It's as simple as that. Sounds like your leak is minor so it's probably an O ring leaking.

hacker-pschorr

I'm still baffled how those are legal to sell. There is nothing "safe" about R134 which is why it's now being phased out in favor of 1234yf. The European Union banned R134a.

To make this even more entertaining, German automakers are boycotting the replacement 1234yf due to being highly flammable in crash tests:
http://refrigeranthq.com/germany-aut...gainst-1234yf/

How long before these store bought cans are banned and R134a is more difficult to buy than R12?

How much does the new stuff cost? I didn't do an extensive search but O'Reilly's has a 10lb container for $1,300.

At this point might as well top off the R12 system with propane.

docmirror

Agree with all the others on the DIY job of topping up the R134 yourself. However, unless the fittings have been changed, you will need the R-12 to R-134 adapter.

https://www.amazon.com/Interdynamics...+r134a+adapter

Or similar. You can ask for it at your local O'Reillys when you get the top up kit. Advised to get the type of kit where the hose and gauge can fit the small 12oz bottles of R134 so that you can just buy the R134 at WalMart later. Follow the instructions on the hose/gauge kit and don't overpressure like I did once and ruined my GM AC pump.

extanker

i would just keep topping it off unless i saw an easy/cheap tell tale leak

Adk46

I've been topping off my car's system (R134). I clearly have a compressor shaft seal leak, maybe at the rear unit, too, maybe all over the place. My dryer may be "full". It works, somewhat, better than nothing.

Before next summer, I'll see what I can do to make it better.

The trick to charging it is to know where the charge port is: underneath the big coolant hose on the starboard side. It takes two fingers on two hands to get the nozzle on the port, on either side of the hose. You'll need to move the intake duct aside first.

I've only been using the goofy single hose method. I wonder how much better it would be with just a new dryer and a proper pump-out and re-charge.

Michael Benno

Thanks for all the replies. I am tending towards the refill strategy if I continue to get a full season out of it. Let me tell you, it's pretty easy to justify a few hundred dollars when you are sitting in traffic roasting alive.

I will have to check the conversion receipt to see what all was replaced. I can tell you the fittings are converted 134a.

I ready through the DYI O ring conversion https://rennlist.com/forums/attachmen...placement1.pdf and it looks straight forward, and time intensive. So maybe this gets added to the winter projects list.

Captain_Slow

Curt - Where should I be looking specifically on the compressor for evidence of a shaft seal leak? I have found a light green oil drop clinging to what looks like a weep hole on the bottom of the compressor. I thought it was coolant, but it is not. Then I thought it might be the dye that's included in the cans of refrigerant. I'd like to replace all the O-rings. I doubt they were done in the changeover to 134. When full the AC is very cold. I have to refill it probably monthly during summer to keep it COLD.

bureau13

Note that it's not just the o-rings that can/will leak. The flexible hoses used with R12 will allow some R-134a leakage as well. Two are reasonable to replace I think...but there is a section of a third line that is near impossible. I had one of my hoses replaced when I converted, because it had developed quite a large leak. I also replaced my o-rings. After a year, I still have freon in the system, although pressures indicate it could use a top-off, which is expected, I think.

Anyone charging that much for a R-134a recharge (at least now, while it's still easy and affordable to do oneself) is robbing you...although perhaps they are evacuating the whole system and recharging with the proper amount of oil, etc? One of the difficult things to gauge if you have a continuous slow leak is how much oil has also leaked out.

Red Flash

Acutally, I have never converted either of my R12 cars to R134 because of the "why-change-something-that-is-mostly-working" approach. The question for some 928 owners in the future may become, "What does it take to convert an R134 system back to R12?" I am thinking you would have to change a lot of parts to get the other lubrication out.

Michael Benno

bureau13,

Both times I had the AC serviced, the system was evacuated, pressure tests, lubed, and filed with 134a and dye. The first time was done by the shop who did the PPI. He put in about 1/3 gallon. He charged me $75 for the service. He was this crazy one-step shop out in the farm boonies. He was down the street from the car and yes, he did work on tractors too. But he had owned a 944 once so, whatever. That whole PPI experience was crazy. Longer story.

The second time I had it filled was by the local Porsche dealer here. They didn't charge me for the service because it was in for rework. They forgot to tighten my crank pulled after the TB/WP job and felt bad about it. Another crazy story. The dealer added about 16oz of 134a.

I was given a quote for a full AC service buy a shop with $100/hr rate for $150.

Adk46

Lots of green stuff on the clutch, which for a long time made me think I had a coolant leak somewhere above. There has also been a puddle of clear oil (?) underneath occasionally. I reported these observations last year, and was advised that my shaft seal is kaput.

worf928

r134 is a smaller molecule than r12 - so I'm told. More will leak through the same sized o-ring as it gets old.

The factory r134 928 systems in '93.5+ leaked enough r134 to need top-offs every ~4-ish years. (And then, after 8-10 years a replacement of the seized compressor because the 'tards didn't add refrigerant oil.) I've seen a handful of GTSs with service records from new and all of them needed r134 top-offs frequently. More-so for those used in hot climates.