Old question revisited: A/C Capacity?
 

I checked the older posts, and not one did they acctualy put in their post the amount of refrigerant to put into the system. Just had links that were dead and of little use to me.

My Chilton and Haynes books make no mention of how many pounds I should put in.

So today I just refitted my air conditioning system and charged it with about 6oz. EsterOil, and a 2lbs shot of R134a.

Does anyone know the factory specification for the PSI of Refrigerant to put into the A/C System?

The 134 should be around 45lbs.

I think he means 45PSI on the low side.......

I asked this same question a couple months back. I used 20 OZ of R134a, and the system cooled pretty good, but really needed another 4-8OZ to be fully charged.

Oh, huh...

I just dropped in 6oz of Oil
and 2lbs of R134... Maybe that should be good...

My 85 GSL-SE A/C system takes 2lbs of R-12 for a charge.

Hopefully oil that is compatible with R134a? (and... purge existing oil out?)

Edit - Ah, I see you used ester oil... did you purge the mineral oil out?

Yeah I drained, vaccumed, and tested my system before charging it.

I am going to stick with 2lbs then... I still can't find the service informtion for the FB on what the reccomended volume is.

Normally there is the factory A/C sticker under the hood that gives the required OZ of R12 to use. The rule of thumb when converting to R134A is to use 80% of the listed R12 amount. You can also get the R12 amount by calling your local Napa auto parts or other knowledgeable auto parts store. They have a listing intermingled in their A/C catalog that shows the quantities.
On Factory equpped A/C vehicles their is also an adjustment to improve the temp that is located on top of the A/C evaporator core. :-)

[QUOTE=rx7doctor;7397476]Normally there is the factory A/C sticker under the hood that gives the required OZ of R12 to use. QUOTE]

That's what we thought too... But I don't have said A/C sticker...

We just winged it and threw in 2lbs... but after a few days the cooling seems less... maybe add another pound?

Where the hell can I find teh factory specs for the A/C capacity?! None of the service manuals seem to mention it at all!

^ Did you read my entire post?

Heh. Sorry I somehow read over that part XD....


Thanks, I'll let you guys know the measurement when I get the chance to run to Kragen's again.

Specs are not in the 85 FSM either. Perhaps because the ac was a dealer install?

What did your refitting consist of? Unless you shall upgrade other AC components to R134a specifications, there will be decreasing cooling.

If you use R134a in a system designed for R12, the cooling is expected to be less.

Oh, I never knew that... Meh I may eventually retrofit a 3rd gen A/C pump on there if I feel like it XD. But for now its okay... Thanks Kleinke, never knew that about A/C

He drained the system of oil and did all of the right things before adding the correct oil and new R134a. What is recommended if you do not use a retro kit is to replace the receiver drier. There is an additive in the retro kit that allows the usage of R134a in receiver driers that were not originally built for R134a. I recommend whether you use the kit or not to replace the receiver drier when changing over.

Since he has stated that after a couple of days the cooling seeemed less. There is a good chance that there is a leak in the system.

You are correct, those are the minimum recommendations, which also include conversion fittings. Some would recommend to replace and/or upgrade the rubber hoses as well, due to increased porosity from age, and contamination by oil impregnation. It's also recommended to flush the system and replace the O-rings with either NBR or HNBR replacements.

From R12 to R134a, changes are necessary to attain equivalent cooling performance, and similar reliability over time without failure. The inherent thermodynamic capabilities of R134a and R12 are different, such that to achieve the same cooling effect, an R134a system must be scaled to a larger capacity than an R12 system. To speak only of compressors, when compressors designed for R12 are used in R134a applications, there is a 12% drop in cooling capacity and 7% drop in energy efficiency, resulting from the compressor alone. The same condenser, compressor, and evaporator designed for R12, will not and can not achieve equivalent cooling performance with R134a. That is a certainty.

The R134a molecule is smaller than the R12 molecule. Thus an upgraded hose which provides a better barrier to penetration, and tighter fittings throughout the system are needed to achieve equivalent mean time between refrigerant loss of R134a vs. R12. An aged hose is even more porous, and the slow leak of R12 becomes a faster leak for smaller R134a molecules.

In general, components (compressor in particularly) designed for R12 have a shorter mean time between failures when converted to, or used with R134a, even with appropriate lubricant. (Attributed to residual contamination, differences in charging pressures, increased cycling, etc.) Specifically, there are several RX-7 R-12 compressors, but only scattered anecdotes comparing their reliability with R12 vs. R134a. Age itself is again a factor, for the seals in an older compressor may have degraded over time, so that R134a molecules will leak past, even if R12 did not.

Refrigerant amounts for each year and each brand of compressor are listed in the Collision Guides. The Mazdaspeed site has 86-95 RX-7 Guides, but unfortunately no Guide for 79-85. Based on the S4, S5, and S6's smaller amounts of R12, 2 lbs of R134a in an S3 seems like too much. It seems unlikely the S3 capacity was larger than the S4 or S5. Hopefully someone can find the specification to be certain.

Yeah, I hunted thru the FSM and several other manuals, never found any reference to an amount, only the obligitory "Add the proper" or "Prescribed" amount of refrigerant.
My car has no label, unless it was on the compressor. There is something on the compressor, but it is not legible. My car does have dealer added A/C, but I have looked under the hoods of 4 other cars, varying from 79, to 85, all with factory A/C, and none had a label listing the proper amount of refrigerant.
I just winged it, using a R134a charging kit that has a gauge, and quit adding when the second can (10oz each) was empty, even though the gauge clearly showed that more could be added. It worked good enough for me, during the hottest part of the summer. I will likely top it off next year, when the weather turns hot again.
This is the second vehicle I have done this conversion on that had dealer A/C and no label. The other one has been keeping me cool since 1999, though I have to top it off every year. Since the A/C compressor on that one is now 27 years old, I know the front seal is leaking, and has been all along.

The biggest problem with the R134a freon is that it is prone to leakage even in todays vehicles. Most vehicles up until the early 90's are alot more prone to leakage with R134a.

I would have to say that if you wanted any type of longevity when converting to R134a on the Fb's that you have the system flushed first then retrofitted with all new o'rings on the compressor and hose fittings and always replace the receiver drier.