Hi,
Had a good trawl around the internet, but can’t find anything specifically for this model.
Looking for the AC re-charge weight of R134a for Eunos Roadster 1995 1.8L Chassis No. NA8C-304615. Maybe someone has access to technical data for this model. It maybe the spec is different to the UK NA since some components are rumoured to be different, ie the condenser is supposed to have different connections and may have a different capacity.
- My model of MX-5 is: Eunos NA 1.8L 1995
- I’m based near: Watford__
- I’m looking for technical help or recommendations on: R134a capacity__
A good question and one that I’ve been looking for but unable to find a definitive answer to. For my RS Limited of similar vintage, I use the quantity stated for the NB which is 350 grams.
Thanks Robbie. I did find a genuine Mazda 1990 NA workshop manual online some years ago. For the R12 system it stated 800 grams. I found it in the aircon section “U” and “Technical Data” “TD”. Of course, R134a is a totally different system. I’m guessing if one could obtain a 1995 NA Mazda workshop manual, it would state the amount. I presume these may no longer be available.
Yes, I knew that the R12 systems held a massive quantity but I’m sure that an R134a would be a lot less.
So a few days ago I spent 3 or 4 hours searching the web. I found some info on the 1994 to 1997 NA and Miata R134a systems. This is not official Mazda data but from 3rd party sites.
First up is: Find your vehicle's refrigerant or oil capacity || TechChoice Parts
This is a US site and lists as follows: Miata 1994-1997 All Engines R134a 21.00oz PAG 100 8.75oz
(21oz=595gms. PAG 100 refers to the oil 8.75oz=248gms)
Next is: http://ishop.cooldrive.com.au/ts1579045263/attachments/BlogPost/208/GasBook2014Online.pdf
This is an Aussie site and has the following entry: MX5, NA30 94-97 600-700gms.
Another Aussie site:
The above site states: MX5 94-97 650+/-50gms
Another factor which could be considered is that in updating the system from R12 to R134a, Mazda may only have changed the seals and used a R134a compressor. If that was the case there is a conversion formula here: https://www.techtownforum.com/wp-content/uploads/2020/07/techtown-R12-to-R134a-Refrigerant-Charge-Conversion-Charts.pdf
(R12 Charge Specification x 0.9) – 0.25 lbs. = R134a Charge Level
0.25lbs = 113.4gms
The charge of R12 in systems used up to 1993 is 800gms.
So using the above formula (800 x 0.9) = 720 - 113.4 = 606.6gms
Interestingly, again we end up with around 600gms. So it seems reasonable to conclude that the UK 94-97 NA may well have the same system as the US Miata and the Aussie NA30 and possibly also the 94-97 Eunos.
Recently an air con guy charged my 95 Eunos to 425gms. Subsequently, my understanding from the above sites, is that this is the charge for post 1998 NBs. Also for a correctly charged (or overcharged) system, one should not see any bubbles in the site glass on top of the dryer. Mine had foaming bubbles indicating that it was undercharged. It was running cool, but not as cold as I have experienced in other cars.
So I guess I’ve answered my own question but would be interested to know if anyone can add anything to verify the figure of around 600-700gms of R143a
Tony
I have to say I would have guessed this would have been 600-800 grams. Usually there is a way of progressively checking the pressure when adding by incorporating a pressure guage, so the question of volume requirement, provided you have enough available, is not that much of an issue. Do you have a pressure guage?
You also mention seal changes when changing from R12 to R134a. R134a works under higher pressure than R12 so seal changes may well be sensible anyway but as I understand it, standard Nitrile seals rather than hydrogenated Nitrile are sufficient for both systems?
On the MX5 I know that valve upgades are certainly required for an upgrade to R134a, if that is what you are doing.
I’m not converting from R12. The 1995 Eunos has a R134a system. It is this I was having trouble finding the correct charge. Neither my local Mazda dealer nor an air con servicer could tell me.
To corroborate what I was seeing on websites re 600gms of R134a I was suggesting that Mazda may have just upgraded the seals and compressor when switching to R134a post 1994, since when applying the conversion formula, from R12 to R134a we get 600gms which is the same as stated for the 94-97 NA on the websites mentioned above.
I don’t have a pressure gauge, nor do I have the equipment to vacuum the system. Apparently, charging by pressure is unreliable because of the variables of temperature and compressor speed, and I understand most air con companies just vacuum the system and charge by weight.
Also on another website it was suggested that an undercharged system greatly reduces the lubrication of the compressor causing premature ware.
Problem is with these archaic gubbins is the risk of chucking good money after bad.
I had my ( 93 Roadster) AC totally stripped out years back thanks to a matrix leak & a dodgy pump clutch…which seized.
I do miss it on baking hot days, but bar that since it sees little winter use, not a lot.
Useless factoid alert:
The whole system on scales weighs roughly a full tank of fuel…petrol being lighter by volume of course!
I’m simply trying to establish the correct charge for a 1995 NA. The pros and cons of MX5 air con are another subject. Twice in the last 2 years on blazing hot days we got stuck in long traffic jams on the motorway with no way out and the missis got heat stroke both times. Hence trying to fix the air con for those once a year occasions. The 14 degree timing adjustment on the NA takes care of the extra weight of the air con with noticeably extra torque.
R12 was the early a/c system fitted to Eunos 1.6 1989 - 1993
R134a was used in the later systems that arrived fitted to the 1.8 Eunos in 1993.
The components used are completely different, so different condenser, pump, pipework, evaporator; in fact no common component as far as I know.
The Ameriacan Miata is different as the two systems look similar with the same later style pump. This is where I suspect the upgrade to R134a rather than use of a much more expensive R12 dropin replacement may confuse the issue.
You seem to have worked out exactly what is required and also proven that the charge fitted at 425 grams is insufficient; well done sir, go with it, I would. As 425 already in the system, presumably you may be able to just add the extra required in a controlled way to get your system working perfectly.
As already mentioned, these systems are now well past their sell by date with a number of well known issues. Hopefully you will escape these or at least find a way around them - good luck. I know a number who are prepared to spend large amounts of money and time to get aircon working. Not so important in the UK but probably vital in a large part of the US.
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It never worked from when I bought it 10 years ago. Looks like I can fix it for a reasonable outlay. I got it charged a couple of weeks ago with the addition of dye. The only leak is on the short pipe from the dryer to the pressure switch. It is fixed to the front chassis rail with a steel clip. This is where it leaks. I suspect the anode reaction between the steel and the aluminium pipe caused it to corrode through. I found a company that can make a new pipe for not too much. Then a vacuum and another charge of 600gms. Nothing left of the 425gms with the dye. So total projected cost looks around £200.
Yes galvanic corrosion, just pair aluminium with steel and add water.
The worst one on this system is pipe that runs along the top of the condenser. They corrode badly under the ‘P’ clip and the threads are impossible to undo to repair/replace.
Eunos 1.8 condensers are fragile too, more so than the 1.6 from my experience.
Can always get a condenser from the states. Ports configured differently but a specialist could make pipework to fit. The pumps are also available new and direct replacement for yours.
Can’t have the wife frying can we, she may suggest that you sell the MX5 
I regassed the A/C in my 1994 1.8 R134a system today with 650g, all seems to be working well.
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Still trying to fix the pipework here. It’s one of the thin ali high pressure (15 bar/225psi) pipes. One end is bolted to the dryer. That comes out easily. The other end is the potential problem. A steel nut threads onto ali threads at the joint. I’ve been plying it with releasing oil every few days. Judging by how a second hand pipe I bought came off, it will be seized and will rip the ali threads off. Heat will only make it tighter since the nut is steel and the ali, having a greater co-efficient of expansion, will expand inside it. If it messes up, I suppose I could buy some kind of bolt together repair joiner but I heard they are not always successful. Any advise is welcome.
Hmm, maybe try a plumbers release-freezer?
“Hmm, maybe try a plumbers release-freezer?”
Thank you. I’ll give it a go. £7.67 from Screwfix.