AC restoration questions, '93 Mazda RX7

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pete_89t2
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AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Fri Oct 02, 2020 5:37 pm

My '93 RX7 resto-mod project has finally reached the point where I can focus my attention on restoring the A/C system. When I got it almost a year ago it had no A/C components on the engine bay side of the firewall. Fortunately all the HVAC electrical controls, HVAC wiring and interior blower/air handling parts were all intact and unmolested. I plan to restore the A/C to work with R134 (it was originally an R12 system).

So far, I've been able to source a good used compressor for it, which is a Denso TV14C unit. Compressor was bench flushed of old lube and refilled to spec with an Ester lube. I installed the compressor on the motor, and tested the HVAC wiring to ensure the compressor clutch engages when it should (with the pressure switch bypassed temporarily). I've also pulled out the evaporator core to flush it, installed a new expansion valve on it and reinstalled it. Plugged the open ports on the compressor & evap core to keep debris & moisture out for now.

My biggest challenge in this restoration will be the A/C plumbing - even if I can find good used parts (not easy), some of them won't fit because they won't clear the aftermarket turbocharger I'm running. So my game plan to finish is the following:

- Get a Mazda RX8 condenser, which includes an integrated dryer with a replaceable desiccant bag -OR- source the largest generic parallel flow condenser that will fit in front of the radiator, and install a generic cylindrical dryer that will fit in the OEM location.

- In either case, I'll need to fabricate custom AC lines, and put in R134 service fittings, and that's where the questions start:

1. The Denso compressor has 2 pad type fittings on it; the OEM setup had hoses with the appropriate pad fittings to mate with the L/H ports on the compressor - if I can't find the two OEM hoses to salvage the OEM pad fittings from (i.e., cut & weld them to a suitable hose fitting), what are my options for plumbing hoses to this compressor? Are there generic pad to male or female O-ring adapter fittings? If I get the RX8 condenser, I'll have a similar problem there as it uses pad fittings too.

2. The OEM system uses a mix of hard aluminum tubing and flexible barrier hose - I think plumbing the whole system up with hose would be easier, are there any downsides with doing this (other than cosmetic - hard line does look better), assuming I can route the reduced barrier hose where it won't see too much heat or other under-hood abuse?

3. Low & High Service fittings - besides the need to be accessible so I could hook up my manifold gauges to them, are there any other placement concerns I need to account for? As far as easy access goes, putting both of them near the evaporator ports (L on suction side, H on discharge) would be ideal - would that be a mistake?

4. As for AC hose fittings themselves, I've heard good things about the Eaton EZ Clip fittings, which are DIY'er friendly with a reasonable tooling investment for the specialized clip pliers. Another option is to go with the bead lock crimp fittings, build up each line and try to find a local AC shop that can crimp them for me. What are the forum's thoughts on the best type of fittings to pick for a DIY install like this that will last?

Thanks in advance!
Al9
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Re: AC restoration questions, '93 Mazda RX7

Postby Al9 » Sat Oct 03, 2020 2:48 am

What concerns me the most is the oil you used. The slightly smaller TV12 compressors used in R-134A applications came with a ND oil 9 factory fill, that is, double end capped PAG 100, double the viscosity at 212F than Ester 100 (the viscosity you likely used, since that's the most common for auto applications) since PAG oils feature higher viscosity indexes. I've also found a pic of an old Denso TV14EC (code 442500-4232) coming from an Italian car and its label states to use the aforementioned ND oil 9. The thicker 212F viscosity is what helps the vanes seal against the chamber. I would have used a DEC PAG 100 instead of Ester.

Can't tell you a specific brand of oil unfortunately, or someone will prolly accuse me of reading all of this off of *brand name's* booklet.
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bohica2xo
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Sat Oct 03, 2020 7:08 am

If you are putting in a huge intercooler, you will need to be sure that the condenser airflow is not compromised.

Using a larger condenser is a good plan, because of the increased air temperature at the face. Plenty of choices out there. CTS Cadillac condenser has been a good swap for me a few times, as well as the Dodge Magnum / Charger condenser.

Plumbing with 100% hose is not a problem. You actually get fewer joints to leak.

Service fittings at the evaporator are ok. Your low side will give an accurate picture of the evaporator pressure. A second high side fitting in the compressor discharge line can be very helpful for diagnostic purposes .

Bead locks are the best choice. You can find nearly every fitting in a standard bead lock. Easy enough to cut / fit / clock custom hoses. There are 6 segment crimpers out there for sale too.

As for the pad fittings, salvaging the old hose is usually easy... except the RX7 has become a cult car. RX7 hoarders won't turn loose of parts. I walk by a driveway with 5 RX7's in it, all of them in disrepair.

If you can find a good picture of the OEM pad fittings, I will try to find a cross reference for you.
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Sat Oct 03, 2020 4:07 pm

Al9 wrote:What concerns me the most is the oil you used. The slightly smaller TV12 compressors used in R-134A applications came with a ND oil 9 factory fill, that is, double end capped PAG 100, double the viscosity at 212F than Ester 100 (the viscosity you likely used, since that's the most common for auto applications) since PAG oils feature higher viscosity indexes. I've also found a pic of an old Denso TV14EC (code 442500-4232) coming from an Italian car and its label states to use the aforementioned ND oil 9. The thicker 212F viscosity is what helps the vanes seal against the chamber. I would have used a DEC PAG 100 instead of Ester.

Can't tell you a specific brand of oil unfortunately, or someone will prolly accuse me of reading all of this off of *brand name's* booklet.


Yup, the Mazda FSM does specify ND9 oil for R134a applications, and mineral oil for R12. However, the last RX7 A/C system I restored was an '89, which retained it's old style serpentine condenser, so when I did that one I asked the forum the question what if the system doesn't perform as well with R134A - what kind of lube should I use in case I want to switch back to R12? The answer was to use an Ester 100 lube, as it is supposedly compatible with both refrigerants. Anyway, that car has been working fine with the Ester 100 & R134A -- cooling performance was a little bit better with R12 on the hottest most humid days, but the compressor seems quiet and happy running with the Ester. Compressor on that older RX7 is very similar to this one, biggest differences being the pulley (v-belt vs. multi-rib belt) and the inlet/outlet ports.
Last edited by pete_89t2 on Sat Oct 03, 2020 4:24 pm, edited 1 time in total.
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Sat Oct 03, 2020 4:23 pm

bohica2xo wrote:If you are putting in a huge intercooler, you will need to be sure that the condenser airflow is not compromised.


It's a pretty big IC, but it's mounted in a stock like location (i.e., behind the radiator & condenser, which both lean forward at about 40*) So the radiator & condenser get their own unblocked supply of fresh air, and the IC behind them gets its fresh air thru some dedicated fiberglass ducting I fabricated

bohica2xo wrote:Using a larger condenser is a good plan, because of the increased air temperature at the face. Plenty of choices out there. CTS Cadillac condenser has been a good swap for me a few times, as well as the Dodge Magnum / Charger condenser.

Plumbing with 100% hose is not a problem. You actually get fewer joints to leak.

Service fittings at the evaporator are ok. Your low side will give an accurate picture of the evaporator pressure. A second high side fitting in the compressor discharge line can be very helpful for diagnostic purposes .

Bead locks are the best choice. You can find nearly every fitting in a standard bead lock. Easy enough to cut / fit / clock custom hoses. There are 6 segment crimpers out there for sale too.


Thanks! Lots of good tips here, easy enough to add that 2nd high side fitting to the compressor discharge, hadn't thought of that. What is the typical street price on the bead lock crimpers, new or used? I'm guessing I'd need multiple sizes of dies to do all correct?

bohica2xo wrote:As for the pad fittings, salvaging the old hose is usually easy... except the RX7 has become a cult car. RX7 hoarders won't turn loose of parts. I walk by a driveway with 5 RX7's in it, all of them in disrepair.

If you can find a good picture of the OEM pad fittings, I will try to find a cross reference for you.


Lol, tell me about it - and Mazda made it more difficult by having 2 different non-interchangeable A/C systems for the FD RX7s; the parts I have were the factory Denso system parts, so they are a bit easier to come by. The port installed MANA system parts are almost impossible to find. Anyway, I did find a suction hose & pad fitting for the compressor, and have a lead on one for the high side discharge. I took a picture, but it seems the forum won't let me post it cause the file is too big.
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bohica2xo
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Sat Oct 03, 2020 5:29 pm

Yeah, you will need to host the photo someplace else to post it on here.

I have seen some ludicrous FMIC installations over the years here - with posters wondering why the A/C no longer works.

With any sort of changes to the heat exchanger stack, it is always good to make sure the fan is pulling air through the whole assembly, and not bypassing around the edge of one or more component. This can make a big difference at idle and low speeds.

I recall that the RX7 had a unique fan placement and lean on the heat exchangers, but it has been many years since I looked at one.

Bench type (non hydraulic) crimpers can be had in the sub $300 range last time I looked. Usually includes enough dies to get a system done. Check with the site sponsor http://www.ackits.com/ You may have to call them, he has a heck of a time keeping all of his inventory online by himself.
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Re: AC restoration questions, '93 Mazda RX7

Postby Tim » Sat Oct 03, 2020 6:29 pm

bohica2xo wrote:Bench type (non hydraulic) crimpers can be had in the sub $300 range last time I looked. Usually includes enough dies to get a system done. Check with the site sponsor http://www.ackits.com/ You may have to call them, he has a heck of a time keeping all of his inventory online by himself.


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Al9
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Re: AC restoration questions, '93 Mazda RX7

Postby Al9 » Mon Oct 05, 2020 3:33 am

pete_89t2 wrote: Anyway, that car has been working fine with the Ester 100 & R134A -- cooling performance was a little bit better with R12 on the hottest most humid days, but the compressor seems quiet and happy running with the Ester. Compressor on that older RX7 is very similar to this one, biggest differences being the pulley (v-belt vs. multi-rib belt) and the inlet/outlet ports.

Then use what suits you best, keeping in mind that there are awful auto AC Ester oils that will break down very easily.
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Re: AC restoration questions, '93 Mazda RX7

Postby Tim » Mon Oct 05, 2020 7:59 am

I use to buy 55 gallon drums of BVA Auto 100. IMO, best auto a/c oil there was and probably still is.

http://bvaoils.com/wp/products/automoti ... ion-guide/
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Mon Oct 05, 2020 2:41 pm

Bear in mind that A19 has never actually fixed an A/C system himself. He has a lot of opinions about things he has never actually touched.

I have used lots of BVA 100 over the years as well. Including use in R4 compressors here in the desert. And the wing cell compressors as well...

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