AC restoration questions, '93 Mazda RX7

[Cusser]

I believe most Mazdas of that era used Sanden compressors with a high pressure relief valve on their rear side.

[Tim]

Supercool is a know a/c lube in the industry. Been around a while. Don't think you got a poor/awful lubricant.

[bohica2xo]

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 ... adid=17571

[pete_89t2]

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 ... adid=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.

[bohica2xo]

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.

[pete_89t2]

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?

[bohica2xo]

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 ... adid=13152

https://www.autoacforum.com/messageview ... adid=14922

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

[pete_89t2]

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 ... adid=13152

https://www.autoacforum.com/messageview ... adid=14922

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

Lots of good info above and in those referenced threads - makes sense to smooth out any sharp edges on the old fittings when using barrier hose on them. Might not be clear in the picture I posted, but those are not really barbs on those fittings - they look to me more like machined O-ring grooves, though when I got the hose off there was no sign of any O-rings ever being in there.

Another thought I had was to use a brazed/weld on adapter fitting (beadlock on one end, braze fitting to AL tube on other) on these. Given the dimensions I listed in the previous posts, would the brazed adapters fit over the AL tubing?

[bohica2xo]

Those grooves were the "barbs" . Just like some of the fittings in the links I posted.

Yes, you can Tig weld an aluminum beadlock fitting to the OEM aluminum pipes. I have done it in the past, but it it a one shot deal. Once the beadlock is crimped, you are done.

I think as complex as the OEM pipes are, they probably clear several obstructions that present an issue for a hose. Just as simple to re-use them with a clamp or ferrule. You can buy ferrules, just measure the OD of the hose installed on the fitting first.

Much of the 1960's A/C systems relied on cheap worm drive clamps with few issues. In fact the dealer installed system in my 1993 F150 has worm drive clamps. A good band clamp will hold everything the hose will.

[Dougflas]

Some of the fitting barbs were made of steel also.