Defrost, fresh air blowers, hamster tubes, frunk fires...

[Tremelune]

Okay, good times. During my on-its-way-to-epic journey of restoring heat to my ’84 coupe, I noticed that a ton of cold air is coming in through the defrost vents. That’s no good, as the heat is having trouble keeping up (in its rather weakened state).

I would like to prevent cold air from getting into the cabin, and I figure (while I’m messing around), I would like to get defrost working admirably. Defrost is good, and good defrost likes lots of airflow. I have no real need to blow fresh air into the car (it has windows), but I do want heat on the dash and my feet.

Research

Here is a thread using an aftermarket blower in the smugglers box and some pool tubing: A/C Blower motor/duct to cabin mods on the 78 911 SC

Here is a thread with good photos of the control box (although mine only has three levers): 'Fresh Air Blower Fan' stopped working

Here is a fun thread that describes a fire from the fresh air blower motor, suggesting I should check to see that a fuse has been installed: fresh air blower

Thread that details the hilarious resistor-based fan speed setup (in case I run into that problem): What is correct gap for blower resistor contacts ?

The ubiquitous air distribution diagram:



Diagrams of the blower and distribution system:





From what I can tell, heat/fresh is distributed by the two boxes on either side of the blower. It is unclear if the blower motor even blows heat to the defrosters...That might be handled by the footwell blowers.

My system

And then there is my car. It is being brought back to street from being track only, so there are some...peculiarities. It is an auto-heat car, but I have little interest in retaining that functionality. The system as it sits:



Smuggler's box (which used to house AC stuff, I imagine):



A close up of the passenger side...Three things worth mentioning: 1) A hose is detached. 2) There is a hole taped up below the blower (which presumably attach to the inlet the hose was attached to. 3) There is nothing attached to flap control arm. Does anyone know which way is "heat"? I'm happy to lock it into place like that.



Here is the state of the passenger footwell. Dunno what went where.



Here is a close-up of that taped-over hole:



Tasks

1) Ensure that no fresh air is leaking into the cabin. Possibly block off all fresh air intakes.

2) Ensure that heat is properly distributed to the dash and footwells via the controls.

3) Get the blower blowing. Probably by installing a dash switch.

I could not find any photos of the stock setup (and of course, they changed over the years). As well, I can't find any air flow diagrams from the perspective of the front distribution system. Any help would be appreciated.

[SpyderMike]

That is the fresh air blower...it pulls air in from the fresh air vent above it and blows it to the mixers. You want to shut the outlets (the long rod across the blower does this). I think you want to pull the rod to the driver's side until it stops. The butterflies on each end have a foam seal that should close it off. It looks open to me. You do not want that fan to run if you are trying to heat things up. The footwell blowers do provide the heat.

[SpyderMike]

The heat from the footwell blowers is routed to the mixers. The bottom of the mixers under the dash is what I have circled in red.

[SpyderMike]

Here is the best diagram I can think of...check this thread:

Retrofitting non-A/C ventilation ducts

[Tremelune]

Nice, those diagrams are perfect.

I pulled a few things apart and it seems that my fresh air flaps are functioning properly with the controls. The fresh air box is closed off from the system.

With that said, I don't understand how cold air can be getting into the cabin through the defrosters, unless...Oh Eureka, I think it may be the fact that my passenger heat flapper is open to the elements, and that footwell blower may still be blowing...Might be specific to my machine. Lemme just see here...

[SpyderMike]

The fresh air flaps at the ends of the fresh air blower need to be full shut.

The mixer valves (items 4 and 5) should be positioned to full heat and no fresh air. I don't have mine installed any more, so I can't check which way those levers should go, but yours look mid-position maybe.

That hole to the smugglers box (red duct tape partially covering) will let in cold air.

Check that both footwell blowers are working - each one works a side - check for heat blowing out of the defrost or under dash vent on each side.

By the way, the duct circled in this picture is where my center vent come out. This could let cold air in from the frunk.

[SpyderMike]

One more thing:



The yellow is the drain hole for the evaporator - clear path to under the car - cold air.

The red is the duct going to the taped red duct taped over hole in your footwell. You will want to close those up.

[Tremelune]

Thank you, this is all a big help.

Random thread with more info about these tubes: Retrofitting non-A/C ventilation ducts

[Tremelune]

I'm not entirely sure what did it, but this pretty much solved the problem:

1) Tape up minor crack in left side defrost tube.
2) Press center AC inlet into place (it was loose) and tape it off.
3) Tape off big hole in smuggler's box.
4) Remove right side blower and tape off the inlet.

I'm going to do some work on the footwell blowers to make sure they operate properly and quietly.