Engine Size: 4.2 L
Refrigerant Type: 134
Country of Origin: United States
I am replacing the evaporator, expansion valve & receiver on this car. I have had the car since it was new with no A/C problems over the first 200k miles. This fall I lost A/C with the bad familiar smell in the car. I took it to my local Mercedes dealer and the mechanic that I have worked with for years evacuated the system, recharged it and checked for leaks. After checking the compressor, all connections and ports, the only leak he found was inside the car at the AC vents. I bought the evaporator, expansion valve, receiver and o-rings from Tim at AMA. I just began the tear down last week. I have installed all of the parts using red Nylog on all of the o-rings. I had to bend the outlet pipe from the receiver about 10 degrees to get it to match up to the new receiver. After the first evacuation, it leaked down in 10 minutes. I could see a pinched o-ring on the temperature switch at the receiver. I had used the wrong o-ring, it was too thick. I used the correct o-ring and evacuated the system again. Vacuum was better at around -30 psi, but after 3 hours I had leaked down about 2 psi to 28 and lost all vacuum over night. I evacuated the system again and charged the system to check for leaks. I found no leaks around the evaporator, expansion valve or ports. I had a small leak at the receiver connections and since the 2 switches and 2 connections are so close, I can't easily tell which is leaking. My Benz mechanic suggested using OEM o-rings to see if that stopped the leak. I changed out the o-rings with no success. The only thing I can think of at this point is to connect the original OEM receiver to see if I can evacuate the system without a leak. If so, buy an OEM receiver. If the original receiver connections leak, could one of the switches have developed a leak since they were checked last fall? One other thought is whether I am applying the nylog correctly. I usually put a string of nylog around the pipe or switch before I place the o-ring. Should I put another string around the o-ring after installing? Any other ideas?
Coat the o-ring with Nylog also. It might help but an o-ring by itself should seal the connection if positioned correctly.
Tim, I will do what you suggested on the nylog. I may have solved my problem. I had not noticed before that I had a leak under the on/off knob of my hose connector.
When I checked it today, it was leaking and collecting down near the reciever which is closed in and no bottom area for the refrigerant to escape. When I checked the whole area behind the reciever, it was sensing refrigerant up to about the level of the reciever. Being heavier than air, I guess that makes sence. I borrowed a friends low side hose. It didn't leak at the connector. I pulled another vacuum to 30 inches, and so far (3 hours), it is holding. If it holds until tomorrow morning, I will consider the problem solved and move on with puting my instrument panel together. Lesson learned is to check your gages & hoses, no matter how good you think they are.
I've never done this over night vacuum check. If it has held that long it is good to go in my book. Always leak check the system after charging.
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