Technical Stupid question awaits you inside...

I'm installing the factory heater system on my 1950 Mercury (it didn't have one before). Should I have the flapper in the vent tube situated to allow air to be pulled in from the cabin when running heat, or from outside air?
Thanx

 

Can't you set it up to do either with a pull of the cable? More modern cars have the choice of recirculating cabin air, which helps to heat up the interior a bit faster on cold days, but using exterior air helps with defogging windows when there is a lot of moisture in the air (my theory).

 

Hmmm, Montana Best recirculate.

 

Since I think my shoebox '51 had a choice the merc should too.

 

Modern cars won't let you recirculate cabin air when using the heater or defrost, only when using A/C. I suspect that is to eliminate the possibility of carbon monoxide poisoning as we tend to leave the car idling in the winter to warm it up and it could build up the level of carbon monoxide in the car.

 

In a high moisture situation outside air works better to help keep the windows from fogging up. A good working heater has no problem heating cold outside air, at least once the engine is at operating temp.

 

Not know the Merc but on the stock heater controller on my 56 the first stop on that control lever opened the right air, the next stop at “heater” closed the right air and directed the air from the front on the car to the heater fan and blew air on to the floor. It had one more stop on the lever which was defrost.
The HEAT actually came from another lever which opened the vacuum controlled water valve and allowing hot water to flow to the heater core.
By not moving the level to open the hot water you can direct outside air to the heater or defroster ducts.

 

A picture would help a lot...My '49 Coupe had a manual splitter damper on the outlet of the fan to allow either the fan to blow into the cabin or fresh air directly to the cabin from inlet grille or any mixture in between..