I learned something new this summer. Over the past 5+ years my wife's E420 developed a slow refrigerant leak. First top-off was in summer 2016, and 1 year later it would have weak cooling again. Of course my mind jumps to a failing evaporator and using sealants but I never got around to that. At the 3rd top-off in 2018, I noticed the pressures were wonky on the gauges. The high pressures were stupid high, over 400psi (!!) in 95F ambients. Normal should be ~225 or so. Cooling was improved but not quite as cold as it should have been, and the compressor never cycled even when driving 55mph. Subsequent testing in lower ambients also showed higher than normal pressures at a steady ~2000rpm. I suspected the TXV was faulty and planned to replace it.
So, in summer 2019 instead of a top-off, I replaced the TXV with aftermarket OEM Egelhof (p/n 140-830-04-84, no COO, but now I suspect it was Chinese). I had also discovered that the high-pressure service port valve had a slight leak so I replaced that at the same time with OE, vacuumed & recharged from a 30-lb tank. I expected pressures to be normal afterwards, and they were. Ice cold air, compressor cycling normally. But, I still thought there was a leak somewhere and figured I'd need to recharge in summer 2020. Summer 2020 rolls around and.... it's still ice cold. Whaa...? Well that's weird. Summer 2021, same thing, ice cold and no issues.
Meanwhile, I discovered something odd on 2 other 1993-1995 W124/M119's with the AC starting to get weak. Both had the identical tiny leak at the high pressure service port. The symptom? The screw-on cap is extremely difficult to remove, you need to use pliers to unscrew it all the way, and there may or may not be a small puff of pressure released as it comes off. In one case there was oil present at the valve, with a hint of bubbling when the gauge was disconnected. Compared to other cars with cold AC and no leaks, the screw-on cap should unscrew easily with your fingers (no tools needed except to break it loose, if over-tightened). Light. Bulb.
I now believe the E420 leak was ONLY at the service port!! And, the weird high pressures might have been due to repeated topping off without evacuating & vacuuming. I'm not convinced the TXV was actually defective but I'm not going to reinstall the original to find out. I'll see if the system is still cold in summer 2022, but it's already a huge improvement going 2 full years with no loss in performance, when previously it couldn't even last 9 months.
The service port/valve is p/n 002-830-54-84. There is a cheap ($5) aftermarket Santech valve and I ordered one to compare to new OE ($20 list, $15 discount). They were substantially different visually; not the same design. It wasn't worth the risk for ten bucks, I used OE and would not recommend the Santech valve. The same valve p/n is used on most chassis in the 90's and 00's.
Key takeaway: Check your high pressure service port, if the system has a charge and is at least cooling a little bit. If the cap is very difficult to unscrew, the valve is very likely to be leaking. If the system is empty (no pressure), this test is invalid. If the valve is leaking, the system must be evacuated to replace it. I'd seriously consider replacing the 2 pressure switches at the drier while the system is empty, assuming everything else is good (cheap insurance).
OE list prices are$60 and $72 in October 2021 ... $56 and $103 respectively (as of March 2024). Edit - $74 / $100, April 2025. Only use OE/Genuine if replacing these switches, there have been reports of failure shortly after installation of the cheap aftermarket switches, and vacuuming/recharging isn't fun - nor cheap.
Note that I have at least 3 different cars with a leaking high pressure service port. I have a feeling this leak may go unnoticed, especially since it WOULD NOT show up when testing with manifold gauges connected (testing either with pressure OR vacuum).
Photos coming later, I have more OE valves on order and will get pics of old OE, new OE, and Santech.
So, in summer 2019 instead of a top-off, I replaced the TXV with aftermarket OEM Egelhof (p/n 140-830-04-84, no COO, but now I suspect it was Chinese). I had also discovered that the high-pressure service port valve had a slight leak so I replaced that at the same time with OE, vacuumed & recharged from a 30-lb tank. I expected pressures to be normal afterwards, and they were. Ice cold air, compressor cycling normally. But, I still thought there was a leak somewhere and figured I'd need to recharge in summer 2020. Summer 2020 rolls around and.... it's still ice cold. Whaa...? Well that's weird. Summer 2021, same thing, ice cold and no issues.
Meanwhile, I discovered something odd on 2 other 1993-1995 W124/M119's with the AC starting to get weak. Both had the identical tiny leak at the high pressure service port. The symptom? The screw-on cap is extremely difficult to remove, you need to use pliers to unscrew it all the way, and there may or may not be a small puff of pressure released as it comes off. In one case there was oil present at the valve, with a hint of bubbling when the gauge was disconnected. Compared to other cars with cold AC and no leaks, the screw-on cap should unscrew easily with your fingers (no tools needed except to break it loose, if over-tightened). Light. Bulb.
I now believe the E420 leak was ONLY at the service port!! And, the weird high pressures might have been due to repeated topping off without evacuating & vacuuming. I'm not convinced the TXV was actually defective but I'm not going to reinstall the original to find out. I'll see if the system is still cold in summer 2022, but it's already a huge improvement going 2 full years with no loss in performance, when previously it couldn't even last 9 months.
The service port/valve is p/n 002-830-54-84. There is a cheap ($5) aftermarket Santech valve and I ordered one to compare to new OE ($20 list, $15 discount). They were substantially different visually; not the same design. It wasn't worth the risk for ten bucks, I used OE and would not recommend the Santech valve. The same valve p/n is used on most chassis in the 90's and 00's.
Key takeaway: Check your high pressure service port, if the system has a charge and is at least cooling a little bit. If the cap is very difficult to unscrew, the valve is very likely to be leaking. If the system is empty (no pressure), this test is invalid. If the valve is leaking, the system must be evacuated to replace it. I'd seriously consider replacing the 2 pressure switches at the drier while the system is empty, assuming everything else is good (cheap insurance).
The red pressure switch 004-820-68-10 is for the low-speed auxiliary fan trigger.
The safety pressure switch is 124-820-83-10.
OE list prices are
Note that I have at least 3 different cars with a leaking high pressure service port. I have a feeling this leak may go unnoticed, especially since it WOULD NOT show up when testing with manifold gauges connected (testing either with pressure OR vacuum).
Photos coming later, I have more OE valves on order and will get pics of old OE, new OE, and Santech.
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