Automotive Air Conditioning Information Forum

I have a 1991 Chevy Caprice that (of course) originally used R12 and mineral oil. The online charts that I find, all say 50 ounces R12 refrigerant, and 8 ounces of mineral oil.

This car hasn't been R12/mineral oil for years. I know that 50 ounces of R134a is too much, and should be less by some varying percentage (that there is some debate about what that percentage should be). But debated refrigerant levels are only half the question. The other half would be... would the PAG 150 amount, simply be the same as the old mineral oil amount?

The condenser is NOT the new parallel flow with the micro tubes. It's the original tube & fin, although it is the type with two separate paths that "Y" apart upon entry, and "Y" back together just before exit. I know many don't like tube & fin for R134a, but the air has been cold enough for me using this condenser on 134 for years (and I like it cold).

The only reason that I even bring up the condenser type, is because I don't know if it might affect the amount of oil needed. It seems like I may have read that the parallel flow with the micro tubes style, may require more oil because of the increased surface area (but I could be wrong about that).

In any event, I would like to know about the PAG amount that I should use in a completely dry system. BTW, the new compressor says that it ships with 3 ounces of oil in it. Would you drain that out and go all new from the bottle, or just count it as 3 of your systems total ounces?

I watched a video from the compressor manufacturer, that indicated...

R134a = 80% of R12 amount.

PAG oil = 20% of R134a amount.

This was said in the context as a good guideline, not a hard-fast rule. However, when applied to my question, the result is interesting...

80% of 50 ounces R12: 50 x 0.8 = 40 ounces R134a

20% of 40 ounces R134a: 40 x 0.2 = 8 ounces of PAG 150 (which happens to be the same amount of the original mineral oil)

Is this a good guideline? Is 40oz R134a + 8oz PAG 150 a reasonable result??

I can see how this would only be a guideline, especially if TF and PF condensers require different amounts of oil (which I'm still not sure if that's been established). BTW, the compressor manufacturer's video answered my question about the oil shipped in the compressor (use it, and it counts).

"Would you drain that out and go all new from the bottle"
Definitely. You don't really know what or how much is in the new comp. unless you do it yourself. Be sure to rotate the compressor shaft a dozen turns after you add the oil

Why are you changing the comp? What happened? If the old one grenaded then you have bigger issues at hand.
Be sure the weight of the PAG matches the weight specified on the comp label. We see way more PAG 46 nowadays.

I am glad your old condenser works for you with 134. It usually doesn't. 134 really needs more fin density and the PF is really the way to go. They are not expensive. I am sure Tim has something for you.

I am not aware that the oil quantity is based on the type of condenser. Others may override me.
I was always taught for a totally dry system, even with PF, the the total oil charge should be 8 oz. You give the comp what it wants then divvy up the rest to the other components. That has always worked here. If a single component is being replaced, then less, because the rest of the components still have an oil coating inside.

70-80% of the R12 charge has always been the rule for 134 conversion as far as I know.

I find the wording in your post a little confusing. On one hand you make it sound like you are doing a fresh conversion to your car, on the other hand it sounds like you are making a repair to an existing 134 conversion

Thank you for your response. That all seems perfectly reasonable to me.

The manufacturer's spec on the oil type is PAG 150. I'm not sure I mentioned it, but the compressor is an R4.

A funny thing about TF condensers and R134a... I have a 1996 Chevy van with both front and rear air (Merry Miler conversion). Being a '96, it obviously was R134a from the factory/conversion company. It still has the original TF condenser in it that came from the factory. I'm not saying that a PF condenser wouldn't improve it's performance, it probably would. I just point that out as a choice that GM made 25 years ago.

As far as why is the compressor being replaced, is another story altogether. It was my own mistake from the previous job. The current components are contaminated from a (my fault) compressor failure. 2 years ago, I replaced every single component in the system with new parts. This includes the condenser with a new PF type, even though I had used the original for years on R134a with good results. At least I did seal the old condenser for storage.

When I say all components, yes, I also mean the evaporator. I'm not sure, but I think I know what my mistake was. The compressor locked a minute or two after starting. The "sick feeling" was immediate. It almost certainly was caused by too much oil in the compressor at one time. I honestly thought that I had turned the compressor (the clutch, not just the pulley) in rotation by hand, 20 to 30 times before I put on the belt. But all things considered, it looks like I didn't.

One thing that surprised me when I pulled off the 2 year old compressor, was no oil came out when I went to drain it. I know for a fact that I put 4oz in the compressor, and 4oz in the accumulator (which may have also been a mistake). But there was definitely 8oz of oil in the system. That's why when I read somewhere about PF condensers taking more oil, I kinda believed it.

Even if I did turn the compressor by hand first, I'm still not sure that the 4oz in the accumulator wasn't too close to the compressor. The suction port is a very short distance from the accumulator. Since I completely charged the system with refrigerant before start up, I'm not sure that the oil in the tank wouldn't have been carried into the compressor at too high a volume.

In any event, I now have a contaminated system. This time, I plan to reuse the original condenser, and the 2 year old evaporator by flushing, and replacing everything else. Flushing seems to be another controversial subject, even among the top dogs on this site (one says quart sized flush bottles are a no-no, the other sells them on his site). So a fella has to try and learn from his own mistakes and move on, as well as parse the information that he reads to make the best decision possible.

Trying to save money isn't always the best course. But it has to be balanced against feasible outcomes. I mean, who really wants a $2,000 air conditioner with a $500 car on it? But yet, the $500 car guy would still like some ac. Anyway, you asked what happened to the compressor, and I have no pride, so...

"I just point that out as a choice that GM made 25 years ago."
They prolly did not know any better at that early time in 134 history, and/or had a huge stock of TFs to unload

I prolly would have put 2 oz in accumulator.
None of us were by your side to see exactly what you did, so all bets are off.

Flushing can be very tricky. It never worked here. I thought Tim had a sticky on this somewhere. Of course you know that a PF cannot be flushed

Good luck!

Yes, that's why I was considering flushing the original TF condenser.

When you say that flushing never worked here, what was the biggest cause of failure?... not getting clean enough, or trapping the solvent, or both?

I haven't found the sticky that you refer to. But it may be the Hecat pdf that Tim linked for me in a post in the flushing section.

Both

If you can get all the flushing agents, oil, and debris removed, I don't care what flushing method someone uses.

I still follow the procedure Hecat wrote a long time ago. Not the easiest or the cheapest.

http://www.hecat-inc.com/FLUSHING%20TEC ... 3-2015.pdf

Just noticed this,

" Since I completely charged the system with refrigerant before start up"

Details on that if remembered. How deep a vacuum, type of pump, etc, the questions go on. Use of refrigerant scale, vacuum gauge, etc etc.

I only bring this up because you are essentially starting over....

tbirdtbird wrote: ↑Mon Jun 07, 2021 7:41 am I find the wording in your post a little confusing. On one hand you make it sound like you are doing a fresh conversion to your car, on the other hand it sounds like you are making a repair to an existing 134 conversion

I just noticed this part of your post. Sorry for the confusion. I called it a "conversion" because of the original system being R12 (and because all the oil and refrigerant charts that I find are mineral & R12 amounts). However, you are correct that this is a repair of an existing R134a system. In fact, as you can tell by a later post in this thread, none of the existing parts have ever even touched R12. Although, if I end up re-using the original TFC, that wouldn't be true anymore.

Thank you and Tim so much for the guidance.