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?