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955/957/958 Cayenne DIY: Clearing the HVAC drain


955/957/958 Cayenne DIY: Clearing the HVAC drain

Old 07-09-2017, 07:07 PM
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Join Date: Mar 2011
Location: Spring Lake, NJ, US of A
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This is copied from another thread - and I had no photos when I wrote it. I borrowed a few from other posts. I will be doing the annual HVAC drain clearing and HVAC filter change shortly - and will try to remember to take more photos at that time to add to this. Meanwhile.. this should be enough to get people started.

Originally Posted by Mike41 View Post
Once in filter area, do I simply pull the hose out and poke in it?

How is the water getting from the AC to this area? Does the drain hose have overflow port or "T" that water backs up into if drain is clogged?
The overflow is from the gasket around the cabin filter. Water will drip out as it soaks the bottom 2" of the cabin filter.

Before pulling the hose out you must:

1. Remove panel under the glovebox. One torx screw. Disconnect the lights/socket so you can move the panel out of the way.

2. Remove footwell vent tube. Pull straight down toward the right side of the vent. It has a plastic clip that goes over a plastic oval nubbie on the body. The left end is simply a push fit into the vent outlet in the HVAC box.

3. Get the cabin filter out. On a 955/957 it's a headed self-tapping screw. I seem to recall buying a special socket for it - probably 5mm. Remove the screw, then reach up with your finger past the end of the door and pull the catch gently back. On the 958 there will be no screw - just the catch - unless the catch has broken and the screw added (that's an official Porsche fix.) Be prepared for a deluge of water (I used a broiler pan to catch it - about a quart..) Put the cabin filter aside to dry out, or throw away and replace (recommended.)

4. Standing on your head (not really, but it feels like it) remove the bastard clamp that holds the drain hose to the HVAC housing. A mid-sized channel-lock seems to be the best tool. Squeeze the two ears on the clamp, and move it down on the drain to where the drain isn't over the water outlet. This should be obvious when you see it. On the 955 I owned there was no clamp. I doubt if a clamp is needed unless you have passengers who like to stuff their toes up under the bottom dash panel and push the hose off the HVAC box. I assume that's why Porsche added a clamp.

Borrowed from a post by ocmacman (thanks!)

Bastard Clamp!

5. Pull that end of the hose off the outlet in the HVAC housing. Be prepared for another quart of water. Have something to catch it in.

6. Pull back the carpet near where the hose goes through it, and grab the large round flange on it and pull it toward the rear of the car. It will pull out of the firewall. It has a flapper closure at the end - chances are that's stuck closed from munge or spiders.

7. Clean the inside of the hose. Then consider removing the flapper. I didn't, and I'm still thinking about it for next time. Is it better to have a flapper that might stick, or to invite bugs up into the HVAC (I have mud-wasps around my house - they're always looking for something like that to build a nest in..)

8. Reinstalling the hose is easy - except for the bastard clamp from hell. Push it back into the hole until the grommet on the end seats in the firewall opening. The big rubber flange goes behind the carpeting not outside the carpeting. Then wiggle the other end back on the fitting on the HVAC box. If the clamp is there - reinstall it I guess. Or take it off and throw it away. Your choice.


Next you have to mop up the water in the footwell. Using your plastic trim removal tools (you have these right? If not - visit Harbor Freight, identical to the ones the parts places sell, but 1/8th the cost..) You can sort of pry the edge of the carpet out from under the door sill guard. I would love to talk to someone who has removed the door-sill guard, since it appears to be part of the kickplate on that side of the footwell, and it doesn't look trivial to remove.

Lots of towels and big sponges pushed under the carpet will help dry it out. Leaving it propped open for a few days will help it dry out.

Be prepared for cuts/scrapes and bruises. Using the AC will actually speed up the dryout time since it dehumidifies the air helping the water to evaporate, and go out the HVAC drain like it should have to begin with.

Good luck. It's not a complex job, just awkward working location and that damn clamp.

Last edited by deilenberger; 05-10-2018 at 11:47 AM.
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