AC Refresh

[dr bob]

Isobutane and normal pentane have the right stuff for a refrigerant, except for that annoying flammability issue. High molecular weight, boiling point almost perfect for a low-pressure system.

My R-134a conversion makes mid-teens center vent temps on 90 SoCal days cruising at 70 with freeze switch bypassed. Hoses and o-rings, new drier, expansion valve. Polyolester oil since I didn't do a full flush. Did drain-and-fill the compressor with the new oil a few times. It's damn cold.

I can't see any reason to stay with R12 or convert to anything other than R-134a.

Ammonia would make perfect sense if you could guarantee no leaks and completely dry the system. In an accident though, poisonous and fire risk.

[Tom]

[blueline]

I wish the TV news report would have said what kind of propane storage or use was involved. Was it a 20lb grill tank or a big outside home type of tank or did the homeowner have multiple tanks stored in an unsafe manor? What set off the explosion? Give people some useful info to maybe prevent it happening again. I'm curious!

News reporting can be so lame with insufficient explanations, especially with these kind of out-of-nowhere headline-grabbing events. Eyeball attraction is apparently the only goal.

[Tom]

I was mostly just being a wise guy about the dangers of propane as a refrigerant, but here's a little more on what happened. Sounds like they used propane tanks in lieu of natural gas, had leaks, and didn't have the requisite odor chemical (or sensors). Your basic 'everything had to go wrong for this to happen' scenario....

https://www.kvue.com/article/news/local ... fd1db8ea75

[blueline]

I figured it might have been something irregular; apparently that was definitely the case. Thanks for the info!

[dr bob]

It's too dark to see the leak, but I can smell it. Gotta match?

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Tl;DR --

Most petro refrigerant substitutes are blends too. So any leaks you might have, even the tiniest, will breath out the smallest molecules first. Any 'top off' needs to be a full charge replace. Any oil in the vacuum pump would get replaced too. Way too many disadvantages. The only 'advantage' I can identify is the 'just dump it into your leaking R12 system' for quick recovery from no AC. Unless you fix the leak, you very soon find that the gas blend is wrong and you get to start over. Once you go that far, replacing o-rings and seals, and the drier since you had the system open, it's just so easy to swap compressor oil and the expansion valve to make it R-134a-ready.

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WTL, Rambling now; Seriously Don't Read --

My 928 came to me at about 16k miles and almost 9 years old, with a thick stack of dealer receipts that might tell me that the car had received excellent dealer-only service its whole life. And it did, except that tracing through it seems that more than half were for "test AC system. No leaks found. Recharge and return to customer". So a from-birth bit of leakage that was easier to recharge than to fix. A a couple cooler SoCal months into my stewardship, AC stopped working. Hmmm. Recharged it with R12. A couple months later (it was winter in SoCal, the weeks around Christmas and New Years when you don't need AC in a black car), no AC again. So parts out on the worktables in the garage, new pieces like compressor hoses and seals from local 928 International. A multi-episode recharge effort, and it freezes fingers on the steering wheel with the anti-freeze switch bypassed.

The AC saga has continued a bit with some 928-specific problems addressed. As far as the basic refrigeration part though, the R-134a is more than sufficient. Thinking about a petro-gas conversion? Um, think better.

[blueline]

Thanks for the dual-post delete Dr Bob - I had no idea it was there until I just now saw your much appreciated correction.

That's what I get for trying to post a reply lengthier than 3-words via a cell phone when I'm away from my phalanx of PCs as I was today. (My post could have used a bit of proofreading too.) I was cursing the silly phone display as I had to turn it sideways to get to the "preview" and "submit" buttons. Then the OSK wouldn't go away and was blocking things.

I know, excuses are like ... the unmentionables. Everyone has one. But still, how glorious is a PC vs a phone when trying to do something longer than a short response.

[gramicci]

I contacted Denso about what lubricant to use. They filled the compressor with mineral oil (R12 compatible so that makes sense) and they said to use use 2.5 oz of PAG 46 ONLY in their compressor along with R132a after removal of all the mineral oil.

[dr bob]

Buying a somewhat generic fitzall PA15 or 20 Denso in the free market will get you one with Denso-named PAG oil. Mine as a R-12 to R-134a retrofit had mineral oil in it demanded a compressor oil swap. Pour the old out, and a few fill/drain cycles with manual compressor rotation is usually enough. A current generic replacement Denso compressor will have that Denso-branded PAG oil in it. If you are flushing the system and getting the old mineral oil out, the PAG will be fine. Not flushing? Any mineral oil left in the system will turn to jelly when PAG mixes with it. Not A Good Idea. POE (polyol ester) is the best option without a full flush. Be aware that both PAG and POE are hygroscopic, POE more so, so open/exposure time is important. Neither is functionally better, but there's a little extra room with the PAG on drier demand. Of course, once the system is closed and evacuated/charged, all of those differences disappear and performance is identical.

I was in my late teens when I took a very basic refrigeration 'course' complements of Chevron/Standard Oil of California. It was hardly the ultimate instruction, but inspired some deeper research. Does that make me any more than an 'internet guru'? Not even close. It has supported some very interesting later work, like geothermal power generation, which can be not much more than a Rankine-cycle AC system running backwards. Six degrees of separation, six extra degrees of cooling?