Hi Scott:

To see the evaporator, go under the hood and lift the plastic cowl panel at the base of the windscreen. Then carefully remove the rubber boot at the blower housing outlet, so you can see to the driver's side and the dirty side of the evaporator. If it looks like a piece of brown/gray felt, you've found a place that deserves some cleaning. A little searching here will get you some options and procedures for cleaning that face of the evaporator. The results are impressive.

 

OMG, so I don't need to pull the blower motor to see it?! That's great news, except I spent last evening on my back trying to find that lower mounting screw!! Looks very clean no? Shocker as the other components were original, assume this is too.

 

Doing this today on my 79 and will post back as I get started.

 

Must be blower day! On my 79 the 3rd screw you have to actually lift the blower door to see it. Then conveniently porsche engineers leave you a open square in the plastic grid to get a screwdriver in. What a time trying to find that screw...

 

I pushed that flapper as far as it would go, no screw. I think it is partway out and blocking the flap from opening farther

 

Its likely there, throw your feet over the passenger seat and lay on your back under ther glove box. Look for the area in the grid that looks more like a square. Get a long Phillips screwdriver. On mine it wasn't a bolt. Prop the flap open,, Stick the Phillips into the hole and just past your vision you will see the head of the screw.

 

Flap should open plenty far enough as the screw is more towards the rear not towards the hinged part of the flap