cant find Ac leak - PeachParts Mercedes-Benz Forum

560slsteve · #1 07-31-2007, 10:09 PM

Well, having completely destroyed and replacing the dash to replace the evaporator, i have yet to solve my AC problem. I have put in the flourescent dyes and found some at the old evaporator, and figured the problem was solved. i have checked all the fittings and the coil (which was new about 6 months ago), and cant find any dye.

So i recharge the system and put in a good shot of dye, run the car for several days and the gauges read 30 on the low and 240 on the high side--the ambient air temp was 96+. i thought the high side might have been too high, ( just figuring out this AC stuff) but i figured that the difference in the pressure was an indication that the compressor was working well. my goal was to just keep gas in the system, and hoping to tweak the gas pressure later, relying on the HP switch to protect things if too high.

2 days later i go on a trip and notice its not as cool---the next day of traveling the AC is doing nothing---i notice the compressor is not running and squeeze the hoses and they are slack, so the LP switch has it turned off.

i get the yellow glasses and blacklight and look everywhere---behind the gauges at the connections, everywhere i can see in the engine compartment, and i see nothing.

the only thing left is the compressor, since i have replaced nearly everything else, including the hoses. i can no oil or dye around or near the compressor, but i have to try to get underneath it tomorrow and look closer.

any suggestions as to what i have been missing? i thought this dye stuff makes it easy to find these leaks--i know its in there because i can see it if i let gas out of the shraeder valve. it seems to me to leak down faster while the compressor is running. after the evaporator was replaced, i put a deep vacuum on the system and it held for about an hour, and the needles then moved down a bit........

after all this work on the evaporator, it is pretty disappointing that this was a partial fix at the most----any ideas will be appreciated.

thanks.

speace · #2 07-31-2007, 10:58 PM

Once I had a leak behind the clutch on the A/C compressor and could not see the dye. There are "sniffer" type tools that are more effeective than the dye.

dpetryk · #3 08-01-2007, 07:38 AM

Since you replaced all the hoses, I was wondering if you tell me in detail how you were able to get the hose connection at the expansion valve off? I was not able to get enough access to get mine off. I had the instrument cluster out and the lower dash stuff off. It looked like I was going to have to remove the steering column and more heater ducting to get at it. I was not willing to go that far then.

I am interested in your experiences.

DOCJBK · #4 08-01-2007, 11:25 AM

I recently changed my expansion valve, it was not easy, there is some duct work that needs to be removed from the side vent, not a problem. The column if I recall only had to be loosened. You do have to work form underneath the dash and through the instument cluster hole. It is slow and tedious. Be careful not to crimp the evaporator lines. I used several box end wrenches and a vise grip. Once the valve is off it is easy to replace the new one. Don't forget to wrap the valve and lines with cork tape to reduce condensation. You replaced the evaporator - why didn't you change the expansion valve when you had the dash a part? Have you replaced the drier? And if you replaced the drier and the evaporator did you replace the copper seals that go with them, or did you reuse the old ones? Each time the system is opened you should replace the drier. Good luck!

560slsteve · #5 08-01-2007, 11:49 AM

depetryk, i can relate to the hose coming to the expansion valve. i think the biggest german on the planet put mine on, and i couldnt get it off under the dash. because i had previously put on a new expansion valve, and was now going to replace the evaporator, i ended up having to get my dremel tool and a cut off wheel and cut the copper tubing behind where the evaporator fitting and hose join. then i had to disconnect the hose from the fuel cooler part under the hood, and pull the hose thru the firewall to get it out.

And then it wasnt easy to break that joint with 2 long wrenches and on the shop bench. i decided i could have never gotten it out under the dash---maybe someone with more strength, but no telling what else they would have broken under there.

its a bear to work under there, and several times i was tempted to remove the steering column, and would have if i hadnt replaced the steering coupler about a week earlier. just didnt want to do that again, but there would have been more room......

good luck with it---i am going to look over my system again this afternoon for any signs of oil or dye ans see whats going on with it. maybe i will get lucky--who knows??

dpetryk · #6 08-01-2007, 08:33 PM

Thanks Steve and Jim for your insights. My system was loosing freon slowly. I ended up finding a number of small leaks. All the leaks were under the hood. They were;

1. High pressure switch
2. O rings at the fuel cooler
3. O rings between the condenser and the compressor hose
4. Crimped hose connection just in front of the left side of the radiator on the high side line running to the expansion valve.

I have eliminated all the leaks except for the high side hose crimp. Since I was not able to get it disconnected at the expansion valve so I left the high side hose in place - for now. My system cools like the north pole. I do not intend to change my expansion valve and I do not want to remove it from the evaporator coil either. When attempting to get the line off, I noticed that it wanted to bend. It needed to well anchored before attempting to remove the high side hose connection. I did not want to bend the line running into the evaporator. So I left it alone for now. Since I stopped 4 of the 5 leaks I just recharged it and left the hose replacement for a rainy day. We will see how long the freon lasts before I need to recharge. The leak is small - near the limit of my detector. So I might be good for quite a while.

Thanks again.

dpetryk · #7 08-01-2007, 08:38 PM

Steve, Its possible that your leak is not fast enough to drag out any oil & dye. You probably need to go at it with a good quality sniffer.

560slsteve · #8 08-02-2007, 10:37 AM

thanks for the replies. as luck would have it, i went back under the gauges and lo and behold i could actually see some dye coming out of the connection where the expansion valve goes into the evaporator. i didnt see it when i initially tested it. but I noticed while running the car that th econnection got very cold and frosted, and was thinking that maybe it loosened up.

so i tried to tighten it a bit, but it still leaked. so today i have removed the expansion valve and retightened with some long wrenches for a lot of leverage that i managed to get into position. I have it under a deep vacuum and so far (an hour so far) it has held. so maybe its fixed this time. i am trying to retighten everything just to be safe---its very difficult to get things tight under there, plus you are afraid to be agreesive thinking about bending and breaking of the line to the evaporator, and believe me, i dont want to go there again for quite a while.

thanks for all the replies and help. i think the leak was so small initally that not much was coming out---in this case, the dye was very local and it was hidden by some insulation that i installed AFTER i had checked it the first time upon re-assembly. I am so paranoid now that i may drive a while san gauges so i can keep an eye on it!!!

thanks again.