AC restoration questions, '93 Mazda RX7

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Al9
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Re: AC restoration questions, '93 Mazda RX7

Postby Al9 » Mon Oct 05, 2020 3:15 pm

Bear in mind that i didn't mean to say that all Ester oils are junk, just that it's easier to run into a junk Ester oil than it is to run into a junk double end capped PAG. I didn't imply that BVA Auto 100 is bad Ester, therefore. Bottom line, take home message, call it however you want, i like to follow OEM specs (and while i didn't fit my new compressor on my car myself, i made sure that DEC PAG 46 went into my new compressor, for that reason; AFAIK, two months have passed and it's still alive and kicking). And Denso doesn't spec Ester 100 for that compressor, that i know. That said, a good Ester 100 might still do its job wonderfully. Didn't mean anything else than that. Didn't comment Tim's suggestion for that very reason.
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Tim
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Re: AC restoration questions, '93 Mazda RX7

Postby Tim » Mon Oct 05, 2020 3:36 pm

Last time I looked. Most OEM never spec a PAG oil for retrofitting. Also OEM for a long time only used SEC PAG oils. I would bet most leading brand POE oils would do as well on a wear reduction test as current DEC PAG's. I'm not against DEC PAG oils at all. Just saying for a retro fit, BVA AUto 100 was a great oil.

I feel the need to balance some claims. Not discrediting yours. Unless read carefully. Some might think this meant more then a few.

"Then use what suits you best, keeping in mind that there are awful auto AC Ester oils that will break down very easily."

I could say.

"Then use what suits you best, keeping in mind that there are awful auto AC PAG oils that will break down very easily."

Both could be true, IMO.
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pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Thu Oct 08, 2020 4:57 am

Wow, I'm surprised my lube selection comment would result in that much discussion - reminds me of what ensues on the Mazda rotary forums when a newbie asks if they should use a synthetic or conventional motor oil in their rotary :lol:

Anyway, the oil that I used was purchased at a local Advance auto parts store. Came in a quart container, brand name is "Supercool"; label says it's a synthetic Ester that is compatible with R12 & R134 refrigerants, and is compatible with PAG & mineral oils. Has a UV dye added to it. Company name on the label is TSI Supercool, from Lake Worth, FL, part # is E32. Also says it's made in the USA. There's also a company website listed, and it says for more info see the SDS - I probably should look that up. Like I said, I've been using the same oil in an earlier FC RX7 project for the last 3 years, and that compressor is running quiet and happy, so my guess is this is a pretty decent lube.

Couple more questions I was concerned about on my AC restoration project:

1. Since the car was originally R12, there was only the one (binary) pressure switch mounted on the compressor - According to the Mazda FSM/schematics, this is a normally closed (NC) switch that interrupts current to the compressor clutch when pressure goes too low (i.e, if much of the refrigerant leaks out). If I convert to R134, I'll need to protect the system from excessive high pressure too, correct?

2. Assuming I need to add protection for over pressure conditions, where should I mount this additional pressure switch? I see that most generic dryers that I can use have switch ports, so using one of those would make life easier.

3. Other than selecting a switch to be mechanically compatible with the switch port, what kind of pressure switching characteristics should I be looking for?

Thanks!
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Cusser
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Re: AC restoration questions, '93 Mazda RX7

Postby Cusser » Thu Oct 08, 2020 7:03 am

I believe most Mazdas of that era used Sanden compressors with a high pressure relief valve on their rear side.
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Tim
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Re: AC restoration questions, '93 Mazda RX7

Postby Tim » Thu Oct 08, 2020 7:22 am

Supercool is a know a/c lube in the industry. Been around a while. Don't think you got a poor/awful lubricant.
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bohica2xo
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Thu Oct 08, 2020 11:55 am

Yes. you should add a high pressure cutout to the clutch circuit.

Blowing the relief valve is something to avoid, and the switch does that. Since you are plumbing fresh anyway, it is not a big job.

Supercool has always been good product Here is a PAG test I did years ago...

https://www.autoacforum.com/messageview.cfm?catid=20&threadid=17571
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Sat Oct 10, 2020 4:01 am

bohica2xo wrote:Yes. you should add a high pressure cutout to the clutch circuit.

Blowing the relief valve is something to avoid, and the switch does that. Since you are plumbing fresh anyway, it is not a big job.

Supercool has always been good product Here is a PAG test I did years ago...

https://www.autoacforum.com/messageview.cfm?catid=20&threadid=17571


Thanks, kind of figured I'd need the switch for high & low pressure cut-out. BTW, in researching this, I found out that what I thought was a pressure switch on that Denso TV14C compressor is actually a thermal cut-out switch, which shuts down the compressor if it over heats. Turns out Mazda's FSM & electrical schematics for the car lost something in translation, but a separate "service highlights" document Mazda published has that missing detail.

As far as selecting a switch, what kind of low & high pressure cut-out switching thresholds should I be looking for if I want to build a system that is compatible with both R134A and R12? Assuming the pressure thresholds for these 2 refrigerants are in the same ballpark, and this is a practical idea (I don't know).

Game plan is to charge the system with R134A, but if I find cooling performance is not satisfactory (and find no other issues that would cause that), evacuate & charge with R12. Which is why I went with an Ester oil that is compatible with both.
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bohica2xo
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Sat Oct 10, 2020 10:43 am

Your RX7 uses a block type TXV, so the low side switch can keep things from operating when it it either too cold outside, or the system is severely undercharged. Both of those conditions can keep oil from returning to the compressor.

An adjustable low pressure switch will do what you want. You can set it to meet your needs for either refrigerant.

I don't recall if your RX7 has a thermostatic sensing bulb in the evaporator to control icing. If it does, then you can set the low pressure switch down around 20 to 25 psi, because the evaporator control will prevent icing.
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Sun Oct 11, 2020 4:18 pm

bohica2xo wrote:I don't recall if your RX7 has a thermostatic sensing bulb in the evaporator to control icing. If it does, then you can set the low pressure switch down around 20 to 25 psi, because the evaporator control will prevent icing.


Thanks, it does have a normally closed thermal switch mounted on the evaporator core. Per the Mazda FSM, that switch opens up at about 32*F/0*C and does indeed cut off the compressor to prevent the evaporator core from icing up.

On another topic for this restoration, I scored a couple of used compressor hoses, and was able to salvage the pad block fittings from both hoses. As I mentioned before, the OEM hoses are useless as-is, because I need to re-route the plumbing to get by the aftermarket turbo. Anyway, I salvaged the compressor pad fittings by using a cut-off wheel to surgically remove the old ferrule/beadlock crimp sleeve from the hoses and get the fittings off the hose. Here's link to a picture of fittings with the hose removed on Google Drive: https://drive.google.com/file/d/1R6gnnw ... sp=sharing

After taking some measurements of the outside diameter of hose end of these fittings, the suction fitting measured 0.572 inches OD, and the discharge fitting measured 0.472 inches OD. Since a #10 hose has a 1/2" or 0.500" ID, and a #8 hose has a 13/32 or 0.40625" ID, will those hoses fit over these fittings? Unless these are some oddball metric hoses, I'm guessing it's a tight fit by design? Also, assuming that's the case, the only thing I should need to attach a hose to these ends will be a beadlock crimp ring/ferrule for the appropriate hose size in standard or reduced barrier, correct?
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bohica2xo
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Sun Oct 11, 2020 5:27 pm

Barrier hose will be a snug fit, but it should be anyway. A little lubrication is a good plan for sliding them on.

If you can't find a loose ferrule with the correct dimensions, you can use clamps. We have covered this before:

https://www.autoacforum.com/messageview.cfm?catid=2&threadid=13152

https://www.autoacforum.com/messageview.cfm?catid=20&threadid=14922

Pay attention to conditioning the old R12 fittings to use the new barrier hose as well. Covered in the threads above.

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