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Thread: AC retrofit: NA8 system in an NA6

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    Ninja Messiah kung fu jesus's Avatar
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    AC retrofit: NA8 system in an NA6

    I'm starting a project to reinstall my aircon into my Miata. I originally had it in the car, but removed it about 5 years ago. I kept all the parts and left the electronics in the car. I am going to try to document this and will edit the posts with pictures as I have them.

    That system had been converted to r134a when I lived in Charlotte.

    Removing it is something I have regretted.

    Anyways, I bought a complete system used from a '97 about a year ago with the intention of installing it in my car. Physically, the two systems are similar. The 94-97 systems came from the factory with r134 as the refrigerant, previous years was r12. r134a, according to the info I have read is about 80% as efficient as the r12, but is still very effective and less harmful to the environment.

    Moving from California back to NC has moved this project up as a priority. I will also use it to diagnose and gain some practice so I I can fix the AC on my wife's '99.

    Another difference I found between the NA6 and the NA8 is in the wiring. Fortunately, since my car already has it in place, I won't need to lay in the harness. The NA6 uses one relay to control the clutch on the compressor and also to turn on the condenser fan. On then NA8, there are two separate relays; one for the compressor, one for the fan. The pressure switch is also different between the NA6 and the NA8. Fortunately, I just tested the mounting ports and the NA6 switch will fit on the NA8's line.

    (insert picture here)

    Right now, all I am doing is surveying my inventory: what I have, what I need, re-familiarizing myself with where the lines go, how they attach to the chassis, etc.

    I have been looking up parts online to see what crosses over between the two systems. Although I have the complete systems, there is stuff I plan to replace just because "I'm in there". Fortunately for me, too, the previous owner of the NA8 system sealed all the orifices and openings as he removed it. The compressors are a little different because of the refrigerants. The driers are different, the condensers are the same, the expansion valves are the same, the evaporators are the same, the pressure switches are different, the o-rings and seals are the same. I haven't looked at the hoses (the flexible ones), but I am not planning to replace those.

    Right now, I am planning on replacing all the system's o-rings, seals, dryer, expansion valve, and pressure switch. Altogether, it's about $100 in parts. I will use the NA8's aluminum lines with the NA6's pressure switch. I will use the NA8's evaporator because is 5 years newer and has been sealed. I left my evaporator open to the engine bay and I'm sure 5 years of dirt, dust and crud has ruined it. I think swapping them out won't be too difficult.

    In the meantime, while I order parts and assess the install, here's is good OE installation walk through:

    http://homepage.mac.com/akerman/misc/90ACINST.pdf

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    Ninja Messiah kung fu jesus's Avatar
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    Ok, ordered a pressure switch to fit the '92 electronics. Also ordered an o-ring and gasket set for a '97, though it appears the same kit is applicable from 90-05. Also ordered an accumulator/drier for a '97. The Drier is cheap and should be replaced anyways.

    Parts should be here in a few days. I will get some compressor oil locally for installing the rings and also to change the oil in the compressor.

    I am a little tardy taking pics of the hardware so far. I will try to get them soon.

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    2,000 rpm - light wheelspin, no bog here! friday's Avatar
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    A/C repair is one of the car things I really don't enjoy, it can be so fidgety. Do you have access to a machine that can recycle and vacuum the system down properly?


    I take it the east coast humidity has inspired you to get to work?

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    Ninja Messiah kung fu jesus's Avatar
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    I don't have the manifold or vacuum, I plan to have that done. Yes, the humidity made it a little urgent. I agree, it is fidgety work, but it is also pretty straight forward on these cars.

    I took my wife's NB to a shop and was told it held vacuum, it was recharged with dye added and works now. So, at least we have one car with working AC.

    Removing my AC is something I shouldn't have done, in hindsight. As much daily-driving I did in it, it would have been nice to have during the long summers in LA where 100+ temps aren't uncommon.

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    2,000 rpm - light wheelspin, no bog here! jnshk's Avatar
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    Some food for thought if you haven't considered it yet, but if you are using r134a and the NA8 compressor, I would think that the r134a NA8 pressure switch would be a more appropriate choice. I don't have the specs on either of them so they may be nearly identical, but sometimes even a small shift in cycling behavior can dramatically affect the efficiency of the system. I'm also not sure how much (if any) the ECM plays into the control of A/C in these cars, fwiw.
    Active: 1991 Mazda Miata (B-Package), JRSC+MS3 [Daily/Project]
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    I thought about that. The pressure switches are a little different. I went with the '92 switch because of the compatibility with the lines and harness. I wasn't sure what voltage the ECU would expect to see from the later models.

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    Small update. I am waiting for the parts to arrive.

    I took the '97 evaporator core and washed it out with some really hot water, dishsoap and a little bleach. I let it soak for a while, then gently scrubbed it with a bottle brush. The bleach is used in the soak to kill any mold or mildew that was in the fins. It's pretty common for it to grow there and gives you the "musty, moldy" smell when you crank up the blower.




    It was pretty clean, but still had some dirt and grunge that washed out of the fins. Note the ends are capped off with aluminum tape.
    Last edited by kung fu jesus; 06-07-2012 at 07:48 PM.

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    2,000 rpm - light wheelspin, no bog here! moerdogg's Avatar
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    What does it take to "convert" a system from R12 to R134a? My 92's air still blows cold, but I imagine someday it won't any more. I don't use it much up here in NE, but those days when we're heading to the beach and traffic is dead stopped, it sure is nice to have!

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    I am not an expert on this, but there are a couple ways to do it.

    GOOD kits will have uprated schrader valves that connect to the existing valves on the high and low side. From there, A shop will evacuate the r12 in there (assuming there is any left). They will add a compatible oil and the correct amount of r134.

    That is the short version of the story.

    I have read different accounts of r12 still being available, but at a much more expensive rate. A lot of people don't know that when a shop evacuates your refrigerant, they can reuse it. Most places won't credit you for it.

    Ideally, when you convert you should change the accumulator/drier. That is the canister-looking thing on the passenger side of the engine compartment under the upper radiator support. They are pretty cheap, $10-25. Why? r12 and r134 aren't compatible with each other. On a molecular level, the r134 is MUCH smaller than r12. They use different oils. The r12, as I remember, uses a mineral-based oil, the r134 uses something else. Also, if the system leaks and loses it's seal...the moisture in the air reacts with the chemicals (not radioactive) that start to eat away at the drier from the inside out.

    Those recharging kits you see at auto stores are really a waste of money. The proper way to recharge your system is to evacuate it, create a vaccum in it, and monitor it with a set of manifold gauges to see if it holds the vacuum. If it doesn't, you can enter a dye in into the system and look for leaks. There are also chemicals you can use that seal the leaks, but there are varying stories on whether they work or not, based on how they seal. Some system sealants use oils to moisten the o rings, making them swell. Most refrigerant techs seem to agree this is an OK sealant to use. Another type is a chemical that when it reacts with the moisture in the air, hardens and seals the leak. You can sort of guess what can happen if you use that and you haven't evacuated the air and moisture out of the system.

    I am trying to use generalities because I not am expert in these things, I am sort of paraphrasing what I have read. A good number of AC related threads on M.N have a member who is a certified HVAC technician/repairman who explains a LOT of these issues in really good detail.

    The amount of r134 you would use in a converted system is different than you would use versus r12. The amount and type of oil used by the compressor(as mentioned earlier) is different, too.

    I know a lot of people treat the HVAC on their cars like it's voodoo. It's not. It is typically an electrical issue or a hardware issue. If you understand how refrigerant systems work, it's easy to extrapolate and diagnose. Likewise, the electrical systems are pretty easy to diagnose. The electronics are setup in a way to save the entire system if there isn't in spec. It is a system of simple electronic switches and relays. I used the workshop manual on my wife's 99 to diagnose the electronics were good, so I knew if the shop I took it to for a charge said otherwise, I would go someplace else. I was actually surprised how easy it was to diagnose. I just needed a multimeter and a 3" piece of wire as a jumper.

    When I took the NB to the ship last week, they pulled the vacuum on it and used dye. Not only did it hold, but no leaks were found. It held the recommended vacuum for 40 minutes without change. I can only suspect that the previous owner might have removed the system because he used the car primarily as an autocross/weekend toy. Anyways, it is recharged and works fantastic!

    Usually, when a system leaks, the culprit is one of two things: bad o rings or a hole on the system. The entire oring kit is $10-15 and is just labor and a slightly delicate touch to repair. The other cause is a hole in the condensor (the AC's radiator) from a rock or debris. The flexible lines that run on the bottom of the car off the compressor can also crack with age or from debris, too.

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    2,000 rpm - light wheelspin, no bog here! moerdogg's Avatar
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    Thanks for the detailed reply! Agree that most folks treat the system like magic, that will kill you if you look at it wrong. I certainly don't want to be accidentally releasing CFCs into the atmosphere, but if the system is leaking the damage is probably already done. Hopefully I don't need to worry about it for a while yet!

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    Ninja Messiah kung fu jesus's Avatar
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    Update: I ordered a substance called RT201B Nylog Blue.

    It is lubricant/thread sealant for AC/refrigerant systems. It is specifically used on the orings, seals and fittings. It isn't something you can pick up at a hardware store, unfortunately. I bought a bottle for $6 + $11 shipping. It came highly recommended for improving the seal and life of the o rings and connectors on the AC system, so, well, OK.

    BTW, there two types; red and blue. Red is a mineral oil-based lube/sealant for r12, blue is for 134a and other types.

    I found it here:
    http://www.trutechtools.com/search.a...Blue&search=Go

    A neat video about it here:


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    Here is the new pressure switch for the 90-93:


    Interestingly, it has the data printed on it:

    p/n YL-2139A
    HP(high pressure) - 27kg/cmē
    LP(low pressure) - 2kg/cmē

    384psi to 28psi (!!!)
    Last edited by kung fu jesus; 06-07-2012 at 07:49 PM.

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    2,000 rpm - light wheelspin, no bog here! thedguy's Avatar
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    I've been looking at doing something similar to my e30. Something you might look into is finding a "parallel flow" condenser.
    They are built to work with the smaller r134 molecules and improve the temperature reduction of the system.

    Iirc the e30 guys that have gone this route song with the factory r134 conversion parts notice about 10°F improvement over the r12 condenser.

    As always, you're are skill of useful info. Already missing you down this way.

  14. #14
    Ninja Messiah kung fu jesus's Avatar
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    Thanks, man! That is a good idea!

    I already have a good condenser, but if it wasn't I would definitely look into it! The prices are comparable to the bar/fin types.

    For those following along, here is an interesting cutaway showing the differences:


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    OK, started getting the parts ready to upgrade the o rings. I started small, beginning with the capillary tube off the evaporator valve on the, well, evaporator.

    The Nylog came yesterday. I have been enjoying shouting "NYLOG!" at the dog. She couldn't care less.

    Here are some pics:


    this is the capillary tube. It's the smallest fitting, and the easiest, probably.


    You can see the tiny, black o ring on the copper thing to the left side. It wasn't in bad shape! There was oil on it and it was still pliable, not smashed and dried out. I am doing the o rings and nylog as a precaution. the rings are cheap so might as well do them...

    Time to find the matching size preplacement o ring:





    Put the new ring on:



    Adding Nylog to the fittings (both sides) and the ring:


    aaaand I reinstalled the fitting. These fittings don't need a lot of torque. The factory service manual (in the link at the bottom of the first post above) lists the torque settings. The Nylog is like stretchy snot, but easy to clean up. I am applying it as shown in the video I linked above. I am being a bit liberal with it, since it can't clog the system.

    One o ring down, many, many more to come!

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