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Water in Backseat Footwell on Driver's Side - AC Drain Issue Confirmed
Hi all -
I posted previously - I am looking into an issue for a friend involving his mother's 2012 C300. There was a significant amount of water in the backseat on the driver's side.
I wet vac'd it up and dried up nicely. The center drain on the windshield was severely clogged so I cleared that. The two side ones were clear.
Today I cleared the front sunroof drains from between the door jams and blew some compressed air through them from the top.
I ran a measured cup of water through all the drains and retrieved pretty much that exact amount from beneath the car - so I know they are clear. I did notice a little dampness on the driver's side A-pillar but I have to believe that was from me being careless and getting some water in the silver part of the sunroof track.
Took the car on a 30 minute drive to get gas and back and when I returned there was a puddle of water in the backseat again. Being that the carpet was wet from the vent located beneath the driver's seat forward - nothing in front of it or along the sides of the footwell - I have to believe that is where the water is coming from.
The A/C was on - so could there be a problem with the system causing the issue? If there was an evaporator coil leak or drain clog wouldn't there be water on both sides? Would it be that much water even?
Could it be that they car took on so much water from the clogged center drain (it really pooled up in that spot and overflowed) that this was just residual being expelled?
Are there rear sunroof drains?
I've done my due diligence and although there are many mentions of this issue however not many solutions. A lot points to the sunroof drains which I think I have effectively ruled out.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
OK, I now have the same problem with my 2014 C350. Rear driver-side footwell is the only place it is wet. That is a good thing, I guess. I am perplexed because there was water in the little pockets of the rubber floor mat that sits on top of the carpet. We've had a lot of rain this week, so it's been damp and cool. I know the A/C is on by default and could be drying the air when driving, but it seems like a lot of water.
Where are the drain lines for the A/C evaporator and did you find them to be clogged? Thanks
I isolated it to the AC drain lines because I checked the sunroof lines by pouring water in the track and it ran out. The AC lines are at the front of the transmission tunnel under the dashboard on the C300. About four inch long rubber tubes that are removable. If your run the car with the AC on while sitting in one spot you should see water under the car pooling if they are functioning properly. The MB's seem to produce a good amount of for whatever reason.
What I can assure you is that if you see that much water on the top of the carpet when you press on it - there are gallons beneath. There is a ton of sound dampening foam below that works like a super sponge. I pulled the carpet, pressed as much water out as I could and dried it with fans. There are modules below that are also sitting in water - but luckily there are drain plugs. Also I found that the reason you are not seeing it in the front is because there is less foam in the rear. So when the front finally gets saturated it eventually pools in the backseat.
Last edited by MKC103; Sep 27, 2023 at 02:50 PM.
Reason: Typo
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Well, you weren’t wrong about the water in the front. I pulled up the carpet and found water pooled. There are rubber plugs that I removed to let the water drain out. But, I did find the evaporator drain hoses and they were clear.
Yesterday, I blew air down the drain hoses for the sun roof and water did start coming out. So my problem may be the sunroof drains.
From what I have read some people have reported dampness/staining on their A-pillars when the sunroof drains are clogged. I didn't find any so I focused on the AC drains.
Make sure you do see condensation under the car when you run the AC.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
My A-pillars are black, but there’s no apparent stains. I got under the car and found the evaporator drain hoses and both had water dripping from them.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
I forgot to mention (or maybe I did) that the rear MB rubber floor mat had water in the little pockets, which is how I first noticed the rear carpet being wet. Wish I had taken a picture. So, I am a bit confused how the water got there. I can't imaging it spraying from under the driver's seat and there was no indication that it dripped down from the roof. Could the water in the back have gotten so deep to overflow the floor mat?
I forgot to mention (or maybe I did) that the rear MB rubber floor mat had water in the little pockets, which is how I first noticed the rear carpet being wet. Wish I had taken a picture. So, I am a bit confused how the water got there. I can't imaging it spraying from under the driver's seat and there was no indication that it dripped down from the roof. Could the water in the back have gotten so deep to overflow the floor mat?
Check the rubber door seal. This can leak and let water accumulate on your rubber door mat.
Yes it can get that deep. I noticed I had an issue because when I stopped short after a long drive I heard a sloshing sound from the rear. It was enough to have to wet-vac it out.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by MKC103
Yes it can get that deep. I noticed I had an issue because when I stopped short after a long drive I heard a sloshing sound from the rear. It was enough to have to wet-vac it out.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
It seems my problem is only on the driver’s side. I removed two more plugs to allow the water to drain. The holes seem to be protected by the under splash shields from taking in water unless I drive through very deep water.
I'm not 100% convinced that whatever blockage there was to cause the issue doesn't somehow work itself out. Everything looked ok to me but the problem hasn't reoccured.
Well you need to solve the issue because from what I understand the connections on that module will begin to rust over time and you will begin to get a whole assortment of electrical gremlins.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
I pulled up the carpet in the back on the driver's side. The carpet was dry to the touch, but soaking underneath. I did remove two more plugs to allow the water to drain out rather than collect.
WRT gremlins, that is my fear. I had a 2008 Infiniti G35x that I bought new. One day I noticed water stains on the A-pillar tan fabric. Pulling up the carpet, I found the same puddled water. By that time, the gremlins had taken over. Once after a heavy rain, the car wouldn't start, and if it did, it wouldn't turn off unless I pull fuses. Called my insurance company and they totaled the car as flood damaged. They paid way more than I could have sold it for and told me that it is cheaper for them to do that than have never-ending repairs for all the electronics that sooner or later would start to act up. I'm hoping that is not the case here.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
A gremlin did sneak in and try to mess with my car. Water got into a connector and shorted out my Flex Fuel Sensor (Fuel Quality Sensor). I blew it away (with compressed air). Details here:
Has your windshield ever been replaced?
I kept finding water on my driver's side weather tech mats and found out the hard way that my windshield seals were bad!
You can test this by running water near the A-Pillar with your trim removed.
Video link of seepage below.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by xxdemo
Has your windshield ever been replaced?
I kept finding water on my driver's side weather tech mats and found out the hard way that my windshield seals were bad!
You can test this by running water near the A-Pillar with your trim removed.
Video link of seepage below. https://www.youtube.com/shorts/yAkw8C5V0so
Good call. I have had my windshield replaced. I will try what the video shows.
There could also be a leak in the small drain hose that connects the sunroof drain to the body drain hose.
Try removing the driver side A-Pillar trim, driver side Rubber Door Seal, driver side Ceiling Handle and then the Driver side Sunvisor. Removal for these is a liitle complicated but can easily be found on youtube by searching "W204 headliner removal"
Pull down the headliner a bit and the inside of the headliner should now be accessible from the driver side and you should be able to see a small rubber hose that connects the sunroof drain to the main body drain.
This hose is just secured by being pushed in and when this is loose (which is more likely) or torn (which is very unlikely) it can also drip water into the cabin through the headliner through the a-pllar down to the floor.
Test by running water into the sunroof drain and see if this hose remains dry.
I found this to be loose and leaking water too into the driver side floor combined by the window seal leak.
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