Brand new A/C from scratch - '88 Mustang

[Maverick9D@gmail.com]

EDIT: Update. System is complete. See post #19 for follow-up question


Hi All,

I recently spent a couple years rebuilding my 1988 Mustang 5.0L and part of that rebuild consisted on reinstalling the AC which i had removed many years ago.

The entire system is brand spanking new. I was able to source many NOS Ford/Motorcraft parts. All the lines are NOS, the EVAP is NOS and i rebuilt the Nippon-Denso 6P148A compressor (which was in excellent condition prior) using a new seal kit. I replaced the internal seals and shaft seal. Everything is clean, fresh, and ready to go. All the older NOS lines had their O-rings replaced with fresh new O-rings compatible with R12 or R134a

The only thing i wasn't able to source NOS was the condenser. As a result, the Tube-and-fin condenser that was original to the car has been replaced by a brand new Parallel flow unit. This is the only non-Ford part in the system.


I'm at a crossroads here. I'm at the point where i can begin putting the system together and adding oil. I've spent a little bit of coin to put this system back together, so i want it to work very well.

I have a supply of R12 dedicated to this car. I can refill the system 3 or 4 times before I run out (not that i want to refill it), so i have enough to use. Question is, should i use it? I need to pick up oil for the system and can't decide if I should use the R12 or just go 134a?

Given the PF condenser, i believe there is a corresponding decrease in system charge capacity. Original fill was 40 ounces of R12. What would be my new level now that i swapped to a PF condenser?

Regarding oil, if i stick with R12, what was the original spec oil for the Nippon-denso 6P148A? I see motorcraft YN-9 was the original spec oil. That's been replaced by YN-9A. I assume this would be ok. If i went with R-134a, which oil would you recommend? This system is all new, so it's free of oil. I believe proper fill capacity is 10 ounces

[tbirdtbird]

"Given the PF condenser, i believe there is a corresponding decrease in system charge capacity. Original fill was 40 ounces of R12. What would be my new level now that i swapped to a PF condenser?"

It is the fact that you went to 134 from 12 that dictates the reduced charge, which should be 80% of the R12 capacity, and we don't use sight glasses with 134, so ignore it.
As far as which refrigerant, I personally would change to 134, the amount you have in R12 might not get you thru the years if service is required. Your call.
If you go to 134, you will want PAG oil, but the viscosity is not clear to me. Also, with a swap to 134, there is a potential issue with the compression ratio of the comp being different, but many cars were converted without regard to that.

Did you change out the drier, or is this an orifice tube system with an accumulator? You did not mention

BTW if you go here, you will find several threads of interest about converting
https://www.autoacforum.com/viewforum.p ... 601e710f18

I don't mind getting you started here, but some of these details are above my pay grade, allow time for the heavy hitters to respond

[akaDigger]

I am currently doing about the same thing as you are. I have decided to go with R-12. The final deciding factor was oil. Our compressors were intended to be lubricated with 500 viscosity mineral oil. The PAG oil only goes to 150. Ester oils, who knows? Best I can tell, ester oil is 100 viscosity.

I am not an ac professional or a chemical engineer. I do not know how these different oils and viscosities perform relative to one another. The opinion I have come to embrace is that I can't go wrong with 500 viscosity mineral oil.

My FS-6 calls for YN2 (Ford std ESA-M2C31-A) 500 visc.
YN9-A is Ford std ESA-M2C31-A Z, 525 visc.

[Maverick9D@gmail.com]

Did you change out the drier, or is this an orifice tube system with an accumulator? You did not mention

It's an orifice tube with an accumulator. I did replace it with a new Ford Motorcraft part. Decal on the accumulator does state compatible with R12 and R134a. Everything is new on the system except for the compressor, which i opened and installed new O-rings/gaskets and shaft seal along with a new NOS clutch unit Compressor looked beautiful internally, no reason for me to suspect it assuming the new seals hold fine.

I admit, i am leaning towards using the R12. I have it, and i'm not afraid to buy more despite the cost.

I guess my questions center around the condenser. I tried to get a NOS tube-and-fin unit, but that ship has sailed, so i bought a modern PF unit, which from what i read is world's better anyway. However in researching this, i did stumble upon a few posts stating that system capacity is reduced when swapping from T&F to the PF condenser. Hence me asking the question.

[Maverick9D@gmail.com]

.
YN9-A is Ford std ESA-M2C31-A Z, 525 visc.

Thanks. From what i can see, the YN9-A superseeds the YN9, so i think i'm good using the bottle that i have. According to the shop manual, capacity is 10 ounces and it does detail out how much to put in each component if doing a new system from scratch, which I am

[tbirdtbird]

you may have missed the 80% rule

[Maverick9D@gmail.com]

you may have missed the 80% rule

Doesn't that only apply when converting from R12 to R134a.

In this case, I'm staying with R12 with the only change being the Parallel flow condenser vs the original tube-and-fin.


Unless i'm missing something??

[bohica2xo]

There is no 80% rule.

Back when refrigerant swaps were new, and the original mineral oil got left in systems - and Ester oil added - there was reduced system volume and higher pressures. So various conversion advice was to reduce charge by 20% to try to control high pressures generated by excess oil and less effective condensers.

If you have a modern parallel flow condenser, and good airflow the system will cool very well on 134a or R12.

Yes, some parallel flow condensers have less interior volume. A lot depends on which condenser you have. Any info on what you used?

Modern DEC PAG oil is fine in older compressors. Or you can use an Ester oil with either R12 or 134a

FYI old "525" mineral oil is NOT 500 weight. Refrigeration oils need s very low pour point "525" is actually ISO 46 grade oil with a -52F pour point.

So, you can actually get much thicker PAG oils - as thick as ISO 150 grade that will still pour below -40 if you really want thick refrigeration oil.

[Maverick9D@gmail.com]

Yes, some parallel flow condensers have less interior volume. A lot depends on which condenser you have. Any info on what you used?

It's a Spectra Premium 7-4453 Condenser.

https://ecat.spectrapremium.com/products/7-4453

[akaDigger]

FYI old "525" mineral oil is NOT 500 weight. Refrigeration oils need s very low pour point "525" is actually ISO 46 grade oil with a -52F pour point.

So, you can actually get much thicker PAG oils - as thick as ISO 150 grade that will still pour below -40 if you really want thick refrigeration oil.

Could you please possibly link to a source that explains this? I have searched but came up short. Possibly just bad search terms.