AC restoration questions, '93 Mazda RX7

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pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Mon Oct 12, 2020 3:52 am

bohica2xo wrote: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.


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?
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bohica2xo
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Re: AC restoration questions, '93 Mazda RX7

Postby bohica2xo » Mon Oct 12, 2020 3:20 pm

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
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Re: AC restoration questions, '93 Mazda RX7

Postby Dougflas » Tue Oct 13, 2020 5:31 pm

Some of the fitting barbs were made of steel also.
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Thu Jan 07, 2021 2:21 pm

Finally got around to finish building up the A/C system on this RX7, but I'm finding after evacuating the system, it won't hold a vacuum over time. So it's likely something is leaking. Quick rehash of the restoration project and summary of where I'm at now:

- When I got the car, the only A/C equipment it had was the OEM Denso evaporator core, and its HVAC controls/wiring was all fully intact and working.
- Removed the evaporator core, and with the expansion valve removed, flushed it out with an A/C solvent. I replaced the expansion valve with a OEM Denso part and new O-rings, and reinstalled the evaporator unit under the dash.
- Picked up a very good condition used Denso compressor for the car; hand turning it it appears healthy, you can feel the compression and suction on the appropriate ports as you turn it. Rotates smoothly with no odd binding or funky noises. FWIW, I got the compressor from another rotary guy who said it was fully functional when removed it from his car (that car was converted to track duty)
- Picked up a new aftermarket generic parallel flow condenser, 24"x12" size which is the largest one I can fit. It was delivered capped and filled with a pressurized nitrogen charge; upon cracking open the 1st cap, I can hear the gas escape, which means the condenser itself is free of leaks
- Picked up a generic aftermarket dryer & binary switch that fits the dryer. Dryer fits in the OEM location/bracket. It too was nitrogen filled, and I could hear the hiss when I cracked open the 1st port
- Due to the turbo I'm running, the OEM A/C hard lines & hoses would not work, so I had to fabricate my own lines and route them slightly differently from the OEM installation. I used all reduced barrier hose (no hard lines) and crimped on bead lock fittings for the hose ends. New proper size green/HBNR O-rings were used on all fittings

Which brings me to today, after closing up the system I pulled a vacuum on it to evacuate and see if the vacuum would hold. The vacuum would only go down to 28 inches Hg. Was expecting 29~30 inHg, but I thought that might be due to cheap Horror Freight vacuum pump i was using. FWIW, same pump on prior jobs would pull a vacuum down to about 30 in-Hg. Anyway, I shut off the pump when I saw it wasn't going to pull anymore vacuum, closed the manifold valves and came back to check the gauges about 10 minutes later. At that point, the vacuum dropped to about 15 in-Hg, and by about 30 minutes later, it was down to zero.

Obviously something is leaking, the question is what? I systematically went over every single connection in the system, opening it up, checking the O-rings, closing it back up & torquing the fitting to spec one by one and repeating the evacuate & vacuum hold drill. None of the connections had any impact on the results, it still lost vacuum within the same period of time.

One concern I have is my manifold gauge set isn't a high quality tool - it's another Horror Freight item, and a tiny leak in any of those fittings would have me chasing my tail to run a conclusive test. Plan A is to see if I can borrow/rent a better manifold gauge set and see if I get the same results, to confirm that the leak is in the car and NOT the manifold gauge set.

Assuming the 2nd gauge set confirms my car's A/C plumbing is indeed leaking, what would be the most efficient way to isolate the leak so it can be fixed?

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

Postby JohnHere » Thu Jan 07, 2021 6:09 pm

I think your plan is a good one. Try another manifold gauge set, pull a vacuum, and see whether it holds. If not, I would suspect the front compressor shaft seal since you've double-checked just about everything else.

Place a shower cap around the front of the compressor, charge the system with a few ounces of refrigerant, and wait a little while. Then, probe under the shower cap with an electronic sniffer and see whether it detects anything. If the used compressor was sitting for some time without being run and the front seal internally lubricated, it could have developed a leak.
Al9
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Re: AC restoration questions, '93 Mazda RX7

Postby Al9 » Fri Jan 08, 2021 6:15 am

Orings have to be lubed (with a non-hygroscopic AC lube/AC o-ring lube, such as the good ol' mineral, and Ester, unfortunately, is hygroscopic).
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Fri Jan 08, 2021 6:30 am

JohnHere wrote:I think your plan is a good one. Try another manifold gauge set, pull a vacuum, and see whether it holds. If not, I would suspect the front compressor shaft seal since you've double-checked just about everything else.

Place a shower cap around the front of the compressor, charge the system with a few ounces of refrigerant, and wait a little while. Then, probe under the shower cap with an electronic sniffer and see whether it detects anything. If the used compressor was sitting for some time without being run and the front seal internally lubricated, it could have developed a leak.


Agree the compressor is the most likely culprit, though I still haven't pulled out the evaporator core to see if the new O-rings installed with the new expansion valve are an issue. Don't think they are bad though, because it's a simple block type expansion valve with 4 o-rings that bolts up between the core manifold and a piping assembly - the design is pretty much idiot proof to assemble & install incorrectly on a bench. That's a great tip for testing the compressor, though I don't have an electronic gas sniffer yet. Hopefully one can be rented/borrowed from one of the local auto parts retailers (Advance, Autozone, etc.)
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Fri Jan 08, 2021 6:34 am

Al9 wrote:Orings have to be lubed (with a non-hygroscopic AC lube/AC o-ring lube, such as the good ol' mineral, and Ester, unfortunately, is hygroscopic).


I purchased the proper O-ring lube along with all the fittings & O-rings and used it, so that's not an issue here.
pete_89t2
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Re: AC restoration questions, '93 Mazda RX7

Postby pete_89t2 » Sat Jan 09, 2021 6:45 am

Another update. My local Advance Auto parts didn't have a manifold gauge set available yesterday, so I couldn't use it verify the readings I got from my questionable Harbor Freight gauges. But I had a thought - can I self-test my Harbor Freight gauge set to see if it holds vacuum on its own, without being connected to the car?

The manifold gauge set in question is this one: https://www.harborfreight.com/ac-r134a- ... 60806.html

What I did to "self test" it was connect the yellow hose to my vacuum pump, and connect the red/blue hoses to their respective quick connect thumbscrew valves as you normally would, but not connect them to the car's service fittings. Keep both thumbscrew service valves on the gauge set in their CLOSED positions, and OPEN both of the manifold gauge valves. Then start the vacuum pump, and draw a vacuum as far as it would go - about 29~30 in-Hg per the low side gauge; high side lacks #'s for vacuum, but the needle goes below the zero mark, and comes close to resting on the needle stop. Turn off the vacuum pump, and let it sit that way overnight. I checked the gauges again in the morning, and both were showing the same vacuum they were at when I left them the day before.

So is that a good test to verify that the leak I'm chasing lies in my car's AC system, giving me confidence that the gauge set is OK?
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Cusser
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Re: AC restoration questions, '93 Mazda RX7

Postby Cusser » Sat Jan 09, 2021 7:32 am

Sounds like your gauge set holds vacuum.

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