AC Evaporator Drain Location

[dukeofchen]

I noticed recently that my car isn't dripping condensation after running the AC, so I suspect the drain tube is clogged.

From what I gather BMW likes to tuck the drain somewhere inconvenient up in the transmission tunnel, but looking from under the car I didn't see one.

Anyone have hints? I'm guessing that I'll need to lower the transmission to have a chance at reaching it.

TIA

[bigjae46]

I noticed recently that my car isn't dripping condensation after running the AC, so I suspect the drain tube is clogged.

From what I gather BMW likes to tuck the drain somewhere inconvenient up in the transmission tunnel, but looking from under the car I didn't see one.

Anyone have hints? I'm guessing that I'll need to lower the transmission to have a chance at reaching it.

TIA

correct

[dukeofchen]

Thanks for the confirmation bigjae46, stuck my whole arm up there and didn't feel anything so it must really be in the absolute worst spot.

Dropping the exhaust and transmission to access the AC drain pipe, classic... 😂

[Slideways]

Thanks for the confirmation bigjae46, stuck my whole arm up there and didn't feel anything so it must really be in the absolute worst spot.

Dropping the exhaust and transmission to access the AC drain pipe, classic... 😂

..

[dukeofchen]

Thanks Slideways this was super helpful.

For anyone else looking to do this, I ended up removing section 1 and the transmission mount, while leaving the driveshaft attached. The couple inches of clearance was just barely enough for me to blindly snake the aerosol tube of evap cleaner up the drain, although if you have beefy hands it might not be possible without lowering the transmission further.

They really couldn't have put this thing in a harder spot to reach. On other BMW models the drain is offset to either side of the transmission and visible without disassembly, while other makes run the tube down to the level of the undercarriage.

At this point I'm in the habit of assuming that the PO never performed anything other than oil changes, so this is what 20 years and 190k miles of buildup looks like after 2 foam treatments.

[simonnim]

Does it smell better?

[dukeofchen]

Does it smell better?

Yep, the cleaner itself had some smell that I'm guessing will wear off eventually. But it didn't smell horrible to begin with, I've been on a quest to optimize my AC system with how hot it is.

By my estimates cleaning the evaporator was worth at least a -5 degree difference in vent temperature relative to ambient, but will be observing over the next few days.

[simonnim]

What product did you use?

[dukeofchen]

These two, the little aerosol tube cap comes with the Kool-It which I got on Amazon, and the coil cleaner is standard stuff for AC from Home Depot.

Not sure if the products are fundamentally any different, but the cap came with the Kool-It and was definitely necessary to snake up the drain tube into the evaporator.

I'll probably post a little summary of the results / process I went through as this adventure comes to an end. This was part 3, after working through refrigerant levels and cleaning the condenser. Might not be as exciting on paper as a performance mod but during peak summer it is to me 😀.

[dukeofchen]

Unfortunately after a week some musty smell has returned, so while it seems this method was effective at flushing a lot of gunk off the evaporator, I didn't get the rest of the housing / system as clean as I would have liked.

I would probably put it down to the fact that after the foam flush you need to run the fan to distribute the foam and push out residual cleaner after it has broken back down to liquid form. And the best way to do so would be to have the engine running to increase airflow.

But on our cars this is a unique challenge unless you manage to access the drain tube without removing the exhaust – or you're willing to run the engine without anything attached from the headers back while explaining to your neighbors that the racecar noises were from servicing the air conditioning.

Perhaps one could access the tube from inside the cabin since it exits somewhere near the gear lever mechanism, or it just makes more sense to go with a different method altogether.

[Slideways]

Unfortunately after a week some musty smell has returned, so while it seems this method was effective at flushing a lot of gunk off the evaporator, I didn't get the rest of the housing / system as clean as I would have liked.

I would probably put it down to the fact that after the foam flush you need to run the fan to distribute the foam and push out residual cleaner after it has broken back down to liquid form. And the best way to do so would be to have the engine running to increase airflow.

But on our cars this is a unique challenge unless you manage to access the drain tube without removing the exhaust – or you're willing to run the engine without anything attached from the headers back while explaining to your neighbors that the racecar noises were from servicing the air conditioning.

Perhaps one could access the tube from inside the cabin since it exits somewhere near the gear lever mechanism, or it just makes more sense to go with a different method altogether.

The drain is under the heater core. Heater core can be removed without taking out the dash. Radio, climate control panel, ash tray and shifter trim have to come out.

[dukeofchen]

The drain is under the heater core. Heater core can be removed without taking out the dash. Radio, climate control panel, ash tray and shifter trim have to come out.

Haha, it seems then this was a fun exercise but at least doing it again won't be as big a deal.

[heinzboehmer]

The drain is under the heater core. Heater core can be removed without taking out the dash. Radio, climate control panel, ash tray and shifter trim have to come out.

Just don't run the engine with the heater core removed!

[bigjae46]

Unfortunately after a week some musty smell has returned, so while it seems this method was effective at flushing a lot of gunk off the evaporator, I didn't get the rest of the housing / system as clean as I would have liked.

I have not seen a way to get rid of the musty smell. Ozone, cleaners, etc...the only thing that I know works is replacing the evaporator. The heater core could also be a source but not as common.

[George Hill]

When these cars were in warranty we would get lots of complaints about musty smells at the dealer I worked at. The #1 thing that we would tell clients and seemed to have the most effectiveness was to always run the car with the A/C on fresh air. I run all my cars this way and I've never had an issue. Im not saying it will work for everyone and maybe it'll be different in other climates but in Texas it seems to be a working option.