DWS964

I had a (big) problem today with the windows fogging up. I have had the slight issues with some fogging when first starting the car after a trip in the rain, but it would soon clear up. Today (rain, changing to snow, temperature dropping from 40F to 33F) the windows fogged up, and would barely keep clear - regardless of settings on the climate control. The windows had cleared a tad shortly before arriving at home, but then I drove through a puddle (well, it's actually a creek. Yes, I have to drive through a creek to get to my house. Not over a bridge over a creek, but through a creek), and the inside of the car really fogged up.
It was time to put on the winter tires, so I checked underneath while up on the jacks. I thought one possibility might be a rip in the orange hoses from the heat exchangers to the diverter boxes. They were OK. The only possible item I found was a shredded rubber boot from the engine fan to the blower. Perhaps the rain was falling into the blower inlet?
Other ideas for a severe fogging problem?

Babalouie

If you need a spare rubber boot, I got one.

DarrylH

Lift your floor mats and make sure the floor and insulation stuff is dry. It's a huge sponge for water so if there's any water getting in the car, it accumulates in the footwell rubber / foam / whatever it is and creates so much humidity in the car the HVAC can hardly cope. That defrost setting on the CCU should be able to keep up with normal dampness, so I'm betting you have something exceptional.

tbennett017

A couple things.. are your drains from the HVAC airbox clear? They come out underneath the car inside the fuel pump hatch. (under the car, just ahead of the passenger footwell) Check to see that the hoses are unobstructed. If they're blocked, moisture condensing with the A/C has nowhere to go.

Is the AC working? Hoses INSIDE the footwells attached and no holes? (either side of the kickpanels there is a hose that feeds the hot engine air up to the airbox)

That engine fan to blower tube does affect the heating air. If it was shredded it might have been affectint the airflow, and maybe drawing in water? (just a guess...)

Makmov

I have to ask because you never said you had it on defrost, which is a seperate button on the control head. That thing blow mega and should clear the windows in a matter of a minute or so. It is just annoying becuase it's loud. Also if you are experiencing real high humidity run the A/C. Sounds silly but that will take the moisture out of the air, you can still run heat at the same time so you don't freeze.

Water from that boot, probably not, that just goes more or less to the ground. You could probably put a garden hose in there and never fill up the HAVAC.

tbennett017

Yes, forgot to ask if you had it on Defrost?... Good question.

I asked about the drains in the airbox (up front) as the water does need to vent, otherwise it can't really dry out. You'll have a pool in there evaporating back into the cabin air.

DWS964

Thanks for the suggestions. Six years of driving 3 different 964's , never had a problem with fogging this badly.
Yes, tried various combinations of Defrost (fans came on "normal" and A/C activated), A/C on, sliders for windshield and floor.
Obviously more moisture was entering the cabin than was exiting.
I checked the drains while I had the car up on jacks - no obvious blockage. There are two drains - one for the evaporator and one for incoming rain, apparently. I did not remove the plate that surrounds the drain hoses (yet), as I have removed it in the past to check the evaporator drain, and it is a pita to get the hoses back in place.
After thinking about it, the shredded rubber boot on the engine fan to blower does not seem to be a root cause. While driving in the rain, saturated air is being drawn into the engine fan anyway and thus into the blower supplying the heat exchangers, so a water leak into the boot would not make much difference in the moisture balance. But, I might just try the "water hose test" and see if it results in fogging up the interior.
I think another possibility is the fresh air intake flap - if I am not getting enough fresh air, then moisture might accumulate inside the car. I have observed odd behavior with the CCU in the past, as it seems to close the fresh air flap and limits the amount of outside air during operation of the AC (until, oddly, I turn up the temperature setting and I suddenly get a flow of air). Pushing the air recirculation button seems to produce no change. In past tests with the Scantool to test outputs of the CCU, the fresh air flap opens and closes.
The drains and the fresh air flap are at the top of my list for pursuit. The 964 Climate Control system operation and logic continues to baffle me.
Keep the ideas coming.