Good Day!

I would like to kindley ask for some advice from the forum members

Background
I am currently working on restoring my 1988 RX 7 to as new (functional wise) as possible, Everything from mechanical to asthetics / comfort and I have finally begun my trial in retrofitting a new air conditioning system into this car
I have already edjucated myself on, hopefully, all the do's and dont's on A/C systems and retrofits:
- Retrofit universal oils aka "death kits" are not wise to use
- R134A is in no way compatible with R12, or R12 systems, mineral oil is in no way compatible with PAG oil
- Condensers cannot typically be flushed out
(etc)

I have all the replacement parts and tools ready for the job, however, I really must ask help on the numbers and logic of retrofits

Questions
1) Because R134A molocules are smaller than R12 molocules you must use "less" yet some places call for 80 - 85% R134A in place of a retrofitted R12 system, and others say to use 75% of your R12 ounce total to R134A, to you, which one seems more reliable?

2) Would PAG oil just be simpily added through the compressor only (and if so, while its on, or off and turning it by hand?) or rather do you need to add it throughout loosley in your evaporator, condenser, and lines and then seal off the system?

3) AC flush is said to be "quick evaporating fluid" however, I am going to assume it is not wise to flush your system and then IMMEDIATLEY plug everything back in so, after flushing the A/C lines, would you let your lines sit in lets say a basement with the ends plugged up with something like tissue so that any residual flush can dry up yet still stay clean?

4) I have located the evaporator behind the glovebox, however, is this removable? As in after disconnecting the lines in the engine bay, would you be able to just disconnect the evaporator from its mounts behind the glovebox and just slide it out, or is there more to it like adhesives or seals?

Thanks for the read!

 

what are your references? educate me!

I don't know how well the OEM system worked, but with the 134a and pag conversion the a/c does blow cool. It just isn't cool enough with the huge glass hatch back (green house). Maybe I will have a professional rebuild the whole system

 

Thats pretty reassuring that retrofits are effective!
You basically answered another question I forgot which was how less effective is R134a, is it pointless, or can it atleast keep you below the range of profusely swetting whenever you sit in the car with the windows up

Honestly my reasources arent really specific, its a combination of whatever I found on here, other sites, youtube, and anything thats remotely relatable in the Haynes repair manual

Here are some examples:
https://www.aa1car.com/library/retrofit.htm
(General retrofit procedure)

One conversion chart that specifies 75% R134A usage
Convert Auto R12 system to R134a ? Ricks Free Auto Repair Advice Ricks Free Auto Repair Advice | Automotive Repair Tips and How-To

And another form that say the rule of thumb is 80% usage
one pound R12=how many pounds R134a? - PeachParts Mercedes-Benz Forum

I remember seeing another form that said to go as far as 85% max, however 75-85% is a pretty big gap

And all of the procedures say to just "add PAG" simple, but does not go into detail if its okay to spread it around the system or only through the compresser

 

When I did a complete restoration on my '89T2 AC system, I ended up converting to R152A (aka - HFC152A or "duster gas" = canned stuff sold everywhere to clean computer keyboards & the like). I was inspired to do this from another thread on this forum, and it turns out elsewhere on the net - Google R152A and you'll see lots of R12 to "duster gas" conversions. Here's the link to the post here:

https://www.rx7club.com/2nd-generati...gerant-964688/

In summary, R152A works just as well as R12 in the FC's AC system, without any of the negative side effects of an R134 conversion (i.e., less efficient cooling with the stock FC AC system parts; compressor has to work harder at higher pressures). I did this 3 years ago on my FC and it still cools as good as the old R12 system did. Also, since this forum doesn't allow linking to posts on other forums, the attached PDF is my write-up from RCC that documents my AC restoration. I started out with a dead compressor, and much like the OP was thinking of an R134 conversion initially.

 

I'm not knowledgable on the FCs specifically, but there are a lot of approaches on this forum for R12 replacements. The 152a/duster stuff is supposed to be the best from what I have read. You'll want to add only 56% of the R12 amount for 152A if you go that route.

There are still some shops/technicians that can recharge your R12 system around (At least in my area), but you or they will have to verify it doesn't have any leaks before charging it.

You might look into using Ester oil instead of adding PAG or additional mineral oil to your system. Ester should work fine with R12 or R-134A.