I searched and did not find any entrance or exit of the cabin air and the heating/AC fan is intended to suck the air inside. Does not it create fogging problems on the windshield in the winter?
Later Pantera's (mid '74 on ???) had a fresh air flapper door that ducted air in from the chamber below the wiper grilles to the heater/evap. unit. Earlier cars just had windows! Also, who drives their Pantera in the winter? But seriously, since properly functioning A/C removes moisture from the air, if you don't have a Pantera with the flapper door, you still have the ability to remove moisture from the air inside the cabin. I'm surprised none of the vendors have come-up with a fresh-air system for Pantera's that didn't come with one. I do recall an article in a POCA newsletter that described how to fabricate and install one. That was probably 20 years ago and the author was POCA's Master Mechanic at the time, Jack Richards. They must have given Jack DeRyke (AKA "Bosswrench") a year off !
I completely restore 4406 and that's why I ask the question because it's time to create an air inlet and outlet if you confirm that you have to roll with an open window in winter when the AC does not work.
I remember some of the old POCA articles (or maybe old PI Tech Bulletin write-ups) n the Fresh-Air options. One I remember used PVC pipe, and dryer hose IIRC, at least one of the "how-to" articles I saw did.
I am sure there may be more elegant solutions.
I don't think a duct for fresh outside air would help, would it? Certainly not in Ventura on a cold foggy night. You need to dry the air in the cabin, lower the dew point, not admit more humid air. It seems to me the easiest way to achieve defrosting would be to fix the air conditioning.
I've driven 6018 on cold foggy nights in Ventura, and for 6 hours in pouring rain, and never had a problem with window fogging. I just operated the air conditioning along with the heater or defroster. If I turned the A/C off for even a brief a moment the windows would start to fog-up.
Besides the '74 factory rig, I've been told the early '71s also had a fresh air inlet. Both these were behind the glove box, feeding the heater/ac boxe from a flex hose. But the vast majority of narrow-body Panteras had none. Kind of difficult to describe the factory assembly and they both take different actuation levers on the console to work.
I was fighting the factory AC at the time so I added vents to our '72-1/2 by carefully measuring, then drilling two big holes in the cowl opening under the removable wiper grilles. You can barely fit a 2-1/2" hole saw thru the vent openings. I used large brass 90 degree sweat-solder fittings of the same size in the holes. The fittings are oriented so they point back at the seats, slightly raised from the cowl bottom so rainwater can't flow in, with 'custom' water baffles on top. These are made of trimmed aluminum beer cans with a big wide slot halfway around the top for air in, sitting on top of the brass fittings & held in place only by the factory wiper grilles that snap in place. No water has entered the car since I did this in the late '80s.
Silicone seals the fittings to the steel cowl and the beer can intakes to the fitting tops. The open ends in the cabin have home-made aluminum throttle blades with little levers and push/pull-rods to open/close the vents separately. One is almost in-line with the driver's left leg, the other is right next to the heater/ac box on the passenger's left. While the openings are not very large, considerable fresh air does flow into the car; more the faster you go. In cold weather, the shut-off valves are necessary! I wrote this up in the POCA Newsletter at the time, and the home-made rig has given some ventilation and no trouble since adding them. Downloads of ALL archived Newsletters are available on POCA's web site.
JB the box in your diagram seems to be the same as my 72 #2636. With a fresh air intake on top under the wiper grates. What do you think? **Edit; or is the air intake at the end of the fans, and the top of discharge .
Rene, it is a lot easier for the HVAC system to "condition" a closed system (X cu. ft of air recirculated) with AC
Adding a constant supply of fresh highly humid air should only aggavate the problem , the cold humid air will flow through the 190*+ degree heater core and turn into heavily moisture saturated hot air. (Simular effect to when you see your breath when it is cold) to cure this the air is "conditioned or dehumidified" by the AC core before hand. Regretfully , I suspect adding a fresh air vent may make it worse.
When I was young I had a butt ugly Mazda station wagon (non working AC) that would ice up the side and back window on the inside, while you were
roasting from the hot air blasting in your face. I cured the problem by buying a Toyota. I guess I could have fixed the AC and still be driving that beast.
How well does that air inlet work shown in JB's drawing? I haven't looked at the heater box very deeply yet but on a quick look I'd think that would be at the pressure side of the centrifucal fan?