Converting R12 to R134a in a Mazda Miata?

[karmavorous]

The AC system in my Miata has not been great ever since I bought it. There's a lot of compressor whine. And it never gets very cool. And this spring it seems worse than the last time I used it last fall.
Many years ago I did a cheap R134 conversion on a couple of older cars. On one car it worked great. On the other car it was not so great.

Two years ago I did a complete R134 conversion on '92 Honda. I needed a compressor anyway. And the cost of all the other parts for an R134 system was cheaper than the cost of an R12 compressor and charging from a reputable shop.

So I did it all myself. It took about 4 hour to do the mechanical part of the job, and an overnight evacuation and charge in the morning and it worked great. It was a very satisfying project.
So I've been thinking about doing the same thing on my '90 NA.

But every Mnet thread or article I've been able to find on google, everybody just drains their R12 system and does the cheap conversion valve kit. Surely there are other differences than just the charging valves between a factory R12 and R134 system???

Anybody know any more about this?

Is it very hard to get to the underdash parts of the AC system in a NA? On my Honda it was all very easy to get to. You just had to take the glovebox out and it was all right behind there. Honda made it easy so that AC could be a dealer installed option on base models. And it seems like I have read in sale literature that AC could be dealer installed on base NAs. Was Mazda as smart as Honda in this regard? Or does the whole dash have to come out?
Has anyone here done an R134 conversion the easy way? Are you satisfied with the performance of the system after the conversion?

I know everybody will say "screw AC, just put the top down"... but where I live it's often not just the heat, it's the humidity - and even with the top down a nice cool and dehumidified breeze can keep me from breaking out in a disgusting sweat... and that means the car can be used more often for commuting to a professional job...
Anybody have any experience in any of this? Converting the AC, or even just removing the AC part from under the dash (how hard is that)?

[NCGreasemonkey]

Cliff note answer. If you are keeping the Miata do it right. Compressor, Receiver / Drier and expansion valve. Good flush through all lines and evap. / condenser with quality solvent. NO FLUSH thru any line with a muffler / filter / resonator! Replace those. New seals through out. Then charge her up to spec. and enjoy.

BTW. The dash is not that hard to remove. And if you have an HVAC box like this it might just have the sealing clamp in this position.



That is how I found mine during dash removal. HTH!

Purchase you a new cluster hood before removing it! It will shatter unless relatively new!!!

[— Phatmiata —]

You can still buy R12 in my area if you know where to look. It's kinda pricey but it's instantly 32F in the car when you turn on the AC.

134a is okay but takes a while to get cold. Wondering if 1234YF will be better or worse. I'm guessing worse.

[NCGreasemonkey]

Hey Randy. If the installer did the old-school 80-85% charge of 134a in your R-12 system that is why it takes a while. Most properly functioning systems that get an equal charge of 134a as they would have R-12 are going to function almost identical.

1234yf is a different creature. And thank someone that we are not using the CO2 based systems that have high-side pressures of around 2000 psi. Eeekkkk!

[— Phatmiata —]

This was on my 96 R-Ltd. converted to 134a and hated it. Vacuumed the whole system and replaced with 134a. Still would not get as cold as the r12 IMHO

I still have R12 in the 93LE and will keep it that way as long as possible.