There have been several threads discussing water on the passenger floor-board due to the AC evaporator/condensate tank’s failure to drain. And the cause that is most often discussed is the elbow-shaped drain tube located on the engine side of the firewall. Reportedly this tube gets clogged with crud, which prevents the condensate from draining outside the car. So with nowhere else to go, the condensate spills over into the passenger foot-well.

I developed the dreaded AC puddle inside my C5, so I jacked up the front end, crawled beneath and found the infamous AC drain tube. I then managed to pull it off the plastic nipple that exits the firewall — easy job so far. Notably, no water came out when I removed the drain tube. Further, I found the drain tube to be clean as a whistle. I felt there was water trapped in the tank, so using a length of rubber hose inserted through the plastic nipple that the drain tube attaches to, I shot a quick blast of compressed air into the condensate tank. A second or two later, water began to flow from my makeshift air hose.

Next I removed the AC fan motor from inside the car and reached my hand into the condensate tank as far as possible. I felt quite a bit of dirty-slim-like stuff near the evaporator and figured that this gunk was probably all over the evaporator core and inside the walls of the tank. I further surmised that the stuff was clogging the water passages that lead to the drain. I felt that the best fix would be to remove the tank and evaporator and thoroughly clean them, but this is one whale of a job.

So I decided to do a quick and easy tank flush. I slowly ran water through the tank with a garden hose inserted through the fan hole and watched for water exiting outside the firewall. When the flow of water from the tank slowed or stopped, I would blow air into the tank from the outside and then repeat the garden hose flush. I flushed for an hour or so and then buttoned everything back up. Then I went for a test drive with the AC on full blast and after thirty minutes, I can report that the water is draining where it is supposed to, outside the car.

Only time will tell if it is really fixed, but I’m confident that I’m on the right track. So if you have an AC puddle inside your car and the drain tube is clean, perhaps flushing the evaporator tank will get the water to drain outside instead of on your floor board.

 

Very good writeup on your procedure. Pictures would help a lot. Who knows, maybe with a full blown writeup, it could be turned into a "sticky" at the top?

 

Thank you there dgrant3830. Unfortunately, I failed to take any pictures during the tank-flush procedure. I'll try to remember next time.