I have a MANA AC system in my car and need to pull the evaporator soon to fix a faulty thermoswitch. I will also need to to replace the drier at the same time and may pull the condenser in the near future if I decide to go with a V-mount. .

I was wondering if it may be just as simple to replace the entire system with a Denso system (which can be found cheaply in the classifieds). An OEM drier is no longer available for the MANA system and the aftermarket one is 6x the price of a Denso ($90 vs. $15) one and does not really fit perfectly. Another possible advantage is that some JDM V-mount kits come with new AC lines - but of course these lines only work with the Denso system.

I have done AC work before on a Miata (and even have a vacuum pump, a recovery unit, and an EPA license) so can deal with the fluids part. I was just wondering if this would really be a direct bolt up and require nothing but new o-rings and fluids or if lots of brackets and other small bits and pieces are necessary. What about the electrical connectors for the thermoswitch, pressure switch, and compressor? My understanding is that the same compressor is used by both systems.

 

As far as I can tell from looking at my spare Denso system, yes it should bolt/plug right in.

 

Thanks for the reply.

Am I right in assuming that the only physical difference between an R12 and R134a Denso system would be the compressor? (O-rings and oil would be different but I'd be using new o-rings throughout in any case.)

 

I believe the thread pitch for the piping is different at the firewall connections between the 93 and 94 systems.

 

Mana systems were metric threads...Denso were in standard

 

Just fyi - Speed of light posted a bunch of info in a few threads on the a/c system. He has the same a/c toys as you - plus a machine shop.

 

Thanks. I'll take a look.

 

Unfortunately, it isn't that simple. From what I've gathered the fittings where the lines attach to one another are different. I know for a fact the condenser has a higher fin density in order to enable it to shed more heat, the expansion valve is calibrated differently (which in truth doesn't impact system performance much), and the high pressure cutoff switch cuts on and off at different pressures. The service ports are, of course, different as well.

As far as oil is concerned, these compressors use a unique oil known as ND-7 for R-12 or ND-9 for R-134a. ND-7 is not mineral oil...it seems to be either a double end capped PAG or an ester. ND-9 is likely a higher viscosity double end capped PAG. Nevertheless, Nippondenso determined that these compressors couldn't use the same oil as all their other compressors.

 

I see. I did a lot of searching and could not find any source for ND-7. I wonder if Ray would have some. I will be calling him this week and will find out.

 

As gracer7 has indicated, this has been covered many times in other threads. For convenience, I will highlight a few things again here:

There are differences: Denso = AN sized fittings, whereas the MANA unit has metric fittings. It's the same physical compressor and is interchangeable, although there may be differences in the seal materials and/or lubricant as required by the refrigerant (as has been noted).

The evaporator thermoswitch is a common FD failure as the load is too heavy for its internal contacts. You can get around this problem (as I have) by using a small "pilot" relay to buffer the thermoswitch output; which can restore functionality without having to pull the evap.. Again, covered in a previous thread somewhere.

FWIW, I run standard sus525 mineral oil in the tv-14 (a '93 originally equipped with R12) used it for years and 100,000+ miles with no problem. If it's an original R134 car, you can use an iso 100 PAG, which is readily available. For those who want to retrofit R12-->R134, use ester. I recommend using either R12, or better yet, an HC refrigerant such as ES-i12a. Avoid R134 as it's a lousy, problematic refrigerant; especially for these systems.

Generally you can reuse the drier indefinitely; especially if the system has been closed--even if uncharged. (That is unless you've suffered catastrophic compressor failure or incurred other major system FOD.) Additionally, the desiccant will be regenerated by pulling a hard vacuum on the system for some period of time, which will flash out most water, especially if the system is warm. If you can get it below 500 microns you will definitely be okay.

 

I had read those threads. I was interested in specific information about a swap, which I have not seen covered. In particular, I wanted information about oils. There were also hints in some of these that the compressor is the same for an R-12 MANA and Denso system, but nothing definitive.

My termoswitch is completely dead so the relay trick will not work.

Thanks for the information about the oil - unlike the ND-7 stuff, it seems to be pretty easy to find. I intend to stay with R-12.

So if I open the system to R&R the evaporator for, say, 30 minutes and immediately pull the system into a ~500 micron vacuum for an hour or so the drier should not need to be replaced? (The system at the moment is fully charged and functioning when I bypass the thermoswitch.)

 

I'm glad my post was of some help.

You said your thermoswitch is completely dead....can you please take a resistance measurement across the contacts--there is still hope for an easy work around that will likely prevent you from having to pull the evap core. I pulled the core and replaced the switch once in my FD, only to have it go bad again a few years later. After some research, I identified the problem and developed the work around which has performed flawlessly for at least 7 years now.

As to the drier, yours should be pristine. Even in systems that have been open for months, I haven't had a problem as they rarely get saturated. With a warm system and a hard vac you'll be fine. Once any moisture has boiled off, the evac pressure will drop pretty rapidly if the system is well sealed--the compressor shaft seal is the usual limitation. Also worthy of mention is that automotive a/c systems are not as sensitive to the effects of minute amounts of residual moisture as your home system that uses a hermetically sealed electric compressors.

 

The current thermoswitch has a resistance of 1.5 ohms. (The new uninstalled one has a resistance of 2.5 ohms or so.) When 12V from a test supply is applied to the input side it of the current one it reads 12V on the output, suggesting that it is operating correctly. However, when installed in the system during operation it will briefly read 1.2V on the output side, allowing the compressor to work, but will then immediately read close to zero volts, effectively shutting off the compressor. The new thermoswitch works ok in this situation (though obviously its probe is not reading off the evaporator).

Is the load too much for it? Can I trust it to work properly to shut off current when the evaporator reaches 0C?

I will try the relay solution in a few days (I have a few lying about my garage). Thanks for the suggestion - I would really like this approach to work.

 

Yes the load is bit too heavy for the thermoswitch; however, the switch will continue to cycle correctly even though there is an increase in contact resistance. The ones I have examined have failed in the 10's to 100's of ohms range(when closed) but will still cycle correctly.

The best solution is to use a small solid state relay, which will draw a minimal amount of current and has a non-inductive input (a good thing). The solid state relay will operate correctly in the presence of substantial resistance--much more than you're likely to encounter with the thermoswitch; therefore, you'll likely never have to bother with this problem again.

 

Tried to IM you because this is getting a little off topic, but your IM limit has been reached.

I am not familiar with solid state automotive relays. Are any of the stock FD relays solid state or are they all the standard inductive coil type? Any particular relay that you would recommend?

 

The answer to your question depends upon what your definition of a relay is. The FD uses many solid state switches (in the form of open collector transistor switches) which, while not relays in the strictest sense, can be construed as relays. Commercial solid state relays add optical isolation between the input and output so as to be a true relay. The primary reason that a solid state relay is preferred for this application is because it provides more gain than its mechanical counterpart, which will allow it to function properly even with a high input resistance caused by a deteriorated thermoswitch.

To buffer the thermoswitch, a small, convenient to mount, general purpose, [industrial] solid state relay which can be sourced from Digi-Key, Mouser or similar electronics distributor will be adequate--something spec'c to operate from at least a 12V input (most will work over a large range) and switch a few amps at 12VDC on the output side. Being physical small, it can mount right behind the glove box and will connect just as you would wire a mechanical relay. You might also check your local hobbyist electronics store, e.g., Fry's, as they'll probably have this sort of thing.

Hope this helps.

 

Thanks. I found on nice Hella solid state automotive form factor relay on eBay, which should do the trick: