Hello,

First of all: No, it's not the coolant flange, or anything connected to it. I just replaced all of that - thinking that was the problem. It's not.

I decided that I had to do some investigating while the engine was hot (cold wasn't helping). I found out that my flange and everything connected to it were fine. The leak is coming from the firewall itself. At the bottom. Right above where the cat meets the exhaust pipe (it's actually over the pipe, but less than 6 inches from the back of the cat). What's even more confusing is that it's just water. Not a 50/50 mix. Just water. No coolant at all.

After about a half a dozen test drives, I finally got it to stop leaking.........but here's the really strange part:

Seeing as how I've been trying to chase down a "flange area" coolant leak, I've been test driving/idling the car with the heater on full blast - never the A/C (for obvious reasons).

After all of my investigating/testing so far today (about 4.5 hours worth). I still haven't lost any coolant what so ever, so I thought "Why not try testing with the entire climate control system off?" (I knew I had full coolant anyway, so no trapped air to worry about).

I ran that bitch hard. Making sure I put maximum stress on all systems (w/o being a fool and breaking ****).

I pulled back into the driveway. Sat and watched........NOTHING. Not a single drip. What the hell does that mean? Does the heater share the same core/evaporator with the A/C? Why would water leak when the heater is on when a.) My heater works fine and blows hot as hell. b.) I'm not loosing any coolant and c.) I recently had my A/C serviced and it blows cold as hell.

I can't wrap my mind around it.

Can anyone help?

Thanks

 

Drive the same route with the AC off and the windows down

 

I've never driven with the A/C on during testing (for obvious reasons).

I've only tried the heater, and completely off. Completely off is the only thing that has worked.

 

Do you mean there is no leak when the climate control is completely off?

 

Yeah,

Every test I've done has been with the heater on full blast and max temp. It leaked water (not coolant) every time.

It wasn't until I turned off the climate control completely that it stooped - completely. Not even a drop (I've tested this multiple times now).

It seems to be coming from some louver type opening in the firewall (on the lower passenger side), then running down the top-side of the heat shielding. Finally dripping from just behind the FR wheel,

I'm not loosing any coolant. My heater blows hot. My A/C blows cold.

WTF?

I'm completely stumped.

 

Ha, funny you mention this. I just finished performing a bunch of maintenance to my brothers 2000 and noticed the same exact "leak" after bleeding the coolant system with the heater blasting. Since it was straight water I didn't worry too much about it.

 

It's the air conditioning, and nothing to worry about. Notice how there is no A/C button like most cars? That's because in a luxury vehicle, they assume you want the best air, no matter what. To turn the conditioned air off, use the ECON button. You'll get better gas mileage that way too, unless you actually need the A/C on.

 

So are you telling me that our cars let the compressor run full-time?

That would make sense.

 

Yup, just checked my brothers owner manual, says it runs all the time.

Bradtyler, it only runs all the time for facelift vehicles though, prefacelift (like mine) definitely have an AC switch.

 

Ahhh. I had a facelifted 99.5 A4 with the ECON button.