Air Con evaporator leak? C320cdi W204

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Merc59

Member
Joined
Nov 20, 2018
Messages
50
Location
Hereford UK
Car
C Class W204
Hi all hopefully this is posted in the correct section of the forum.
My air con on the above 2008 c class stopped working (flashing red light when button pressed) garage had it in no refrigerant they did a vacuum test, it passed and recharged the system Nd ac worked for 1 day.
Rebooked in and they did a leak test using nitrogen no leaks were detected at the condenser, compressor or associated pipes nor anything through vents in car when cabin fan running. Only when they removed the plenum in the engine bay and with fan running tested the fan box and cabin filter box a leak was detected. They are assuming that the evaporator is a fault which requires the dash out to replace.
Having enquired with dealership and another garage they are surprised that this has failed.
Can you let me know your thoughts etc. I am suspicious as nothing was seen on the vents and am wondering if the pressure regulating valve is leaking against bulkhead and the fan pulled it in.
 
I would take it to an aircon specialist for a second opinion . If it lost the gas within a day I would think the leak was there from the outset. Evaporator failure is not that common, but expensive to fix as the dash has to come out.
 
I would pop the lower panelling out where the condenser sits and have a look at the bottom of the condenser.

They do usually go at the bottom due to debris build up......thats where mine went on the same car as yours previously.

The leak detection that they do is generally useless for slow leaks.

Better to heve dye injected and check for the leak with a UV light.
 
I did wonder about this area of the condenser as looking down the gap it is indeed full of leaves debris etc. Have decided to order a new condenser (can be returned if not needed) so if the leak is there I can swap it out there and then. Will let you know what I find next week.
 
Evaporator leaks are very rare, but not entirely unheard of. I have however seen two W204 with leaks where the expansion valve goes through the bulkhead. Loads of dye was seen in the foam surrounding it.
 
Easy way to check for an evaporator leak is to put UV leak detection dye in the system, run the AC for a bit & then shine a UV light over the condensate water that comes out of the drain underneath the car. If the dye shows up in the condensate water then you have an evaporator leak.
 
Cheers guys I did wonder about that valve so also have one of those in readiness with replacement o ring seals. Didn't think about condensate so will get that looked at, even if it means refilling system temporarily to run it. Anything and everything is going to be rechecked before we start pulling the dash.
 
Easy way to check for an evaporator leak is to put UV leak detection dye in the system, run the AC for a bit & then shine a UV light over the condensate water that comes out of the drain underneath the car. If the dye shows up in the condensate water then you have an evaporator leak.
Did this over the weekend and indeed yellow liquid was seen coming from condensate, confirmation as you said leak is from evaporator which means dash out (oh joy) and an expensive bill to rectify (double oh joy). Fortunately warranty on it covered up to £500 of the cost I've decided whilst the system is apart to also replace the condenser, drier and expansion valve to hopefully remove as much contamination out of the system.
 
All sorted definitely the evaporator at fault (which most tell me is very unusual) but changed condenser and pressure valve now have nice cold air con.
 
They pressure tested it and vacuum tested and it held? I wonder how long for.
 
I was there for the initial recharge and investigation. The machine pulled a vacuum and held it for 45 mins but lost the charge in a day. The 2nd visit was to investigate for a leak they pressurised the system 1st with air which lost pressure in a short time but couldn't confirm where leak was using soapy water. They then pressure tested with nitrogen and used a sniffer eventually tracing leak to inside car confirmed evap was issue. The nitrogen also lost pressure during this investigation. I did ask why it held under vacuum they weren't sure but wondered if the leak closed under vacuum. I have the evap and it's covered in dye along the one edge otherwise it looks in good condition.
 
I was there for the initial recharge and investigation. The machine pulled a vacuum and held it for 45 mins but lost the charge in a day. The 2nd visit was to investigate for a leak they pressurised the system 1st with air which lost pressure in a short time but couldn't confirm where leak was using soapy water. They then pressure tested with nitrogen and used a sniffer eventually tracing leak to inside car confirmed evap was issue. The nitrogen also lost pressure during this investigation. I did ask why it held under vacuum they weren't sure but wondered if the leak closed under vacuum. I have the evap and it's covered in dye along the one edge otherwise it looks in good condition.
Because a vacuum is the equivalent of minus 15 psi. Under pressure it's 200 psi plus on the high pressure side of the system.
 

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