Hi all, I wanted to share the story of my AC rebuild process, and hopefully prevent others from making the same mistakes I did. After quite a few false starts and failures I have worked my way progressively through to a 100% rebuild of my AC refrigerant circuit. I am not a professional mechanic, nor do I have any formal training. I do have a good bit of wrenching experience, as well as a history with electronics. Please do not take my word as definitive, I am not an expert, please do your own research and consult a professional if needed.

Part the first: the story so far:

I bought this car in the fall, it had no service history but had a fairly new paint job and almost entirely new interior. I did not do as thorough of an inspection as I should have, however given the chance I would still buy the car today.

It was a chilly morning when I bought the car, so my test of the AC was not very definitive, but it did seem to get cold. That winter I was running into problems with the heater so I ended up replacing the radiator, hoses, thermostat, temp sensors, and monovalve.

Part Deux: The electrical and vacuum systems.

In the course of some other work to the car, I pulled the dash. I knew I had some vacuum pods that were leaking, as well as a broken cabin temp sensor. I sourced some repair diaphragms for the vacuum pods from a forum member and rebuild all of my pods, as well as two faulty vacuum switchover valves, and all of the rubber hoses. With the help of a friend, I determined the correct part to rebuild the cabin temp sensor and repaired that. (PM me for info if you are interested). During the disassembly process I discovered that my CCU (control switches) had previously suffered an electrical fire - there was a hole burnt through the housing. It had been repaired previously with a jumper wire, but I decided to order a rebuilt unit instead, as the PCB was pretty well ruined. I also installed a new auxiliary water pump with a 2amp fuse in series.

Part III: Failed attempts:

The following spring I discovered that the AC only worked on cool days. It had previously been converted to r134a. I discovered that it was leaking at the TXV. I tried some leak stop (bad idea) and added some r134a. Neither of which resolved the problem. Next I decided to try a minimally invasive fix: I had the r134a recovered by a shop, replaced the txv, drier, pressure switch and tried charging it again.

This time the system would not develop suction enough to charge the system, also the compressor was making a horrible noise. Again I had a shop recover the refrigerant I tried to add (only about half a pound made it in). I dismantled the entire system, and ran four cans of flush through it (most of which was used in the evap and condenser. I found several clogs, I believe those were formed by the leak stop product I had used earlier, but I can not confirm that was the cause. I also purchased a new r4 compressor with clutch, and installed it. I had purchased a vacuum pump in the meantime (previously I was using one at a DIY mechanics shop) and tried to pull a vacuum, but was unable to hold a good vacuum (and yes, I am aware a vacuum test is not definitive). I had noticed that the high side line to the condenser was corroded, as well as the fitting on the condenser, so I decided to upgrade to a parallel flow condenser. I ordered a 16x24 condenser with custom mounting hardware and new hoses, and installed it along with a new drier. I finally tried to charge the system again, and was getting somewhat out of proportion high side pressures in comparison with the low side, and was not getting cold air. I then purchased a leak detector and had found a potential leak somewhere inside the evaporator housing when the system suddenly discharged. It turns out that the compressor bolts were never torqued fully, which allowed it to split in half. I never definitively determined if I had a leak other than that.

Part IV: A new system:

I was sick of dealing with troubleshooting a 30 year old system. I decided to replace or rebuild every component possible with new parts, upgraded if possible. This includes:

A Sanden compressor with new mounting brackets.
All new liquid lines.
The compressor kit included a new compressor->condenser hose.
Suction hoses. I will be using the original metal ends that connect to the TXV and the piece that runs across the engine. I will be rebuilding them with new barrier hoses and using crimp ferrules.
A new condenser (Remember that I had previously installed a 16x24 PF condenser).
A new evap. There are two evaps for the w123, one of which is NLA. I have the other style on order and hope it will fit without modifications to the housing. If it is not capable of fitting at all, I may have to have my original one professionally flushed and repaired.
New receiver drier
New pressure switch
New TXV
Possibly a new temperature controlled fan switch
I may install a high pressure switch in the extra port at the TXV, to switch the fan if I am not satisfies with the temperature controlled switch.
A universal fit 16" auxiliary fan.

I will edit or reply to this post with further detailed information and pictures as the rebuild progress continues. I may post detailed DIY guides on individual steps. Please feel free to PM me any questions.

Stay tuned. Up next: dismantling the old system (currently underway)

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild