A/C Question
 

Have almost finished a Rennaire conversion kit I purchased from our host (thanks Wayne!). One quick question: In the smugglers box there are two openings that supply air to the evaporator - one trapezoid shaped opening that goes to the passenger side floor board and the other is a round opening that is not apparent to me where it goes. Can someone tells me where this air supply comes from? Fresh air plenum?

That round hole leads to the tunnel that passes between the seats. In the mid-60's 911's, a gasoline-fueled heater was in the smuggler's box and it got its return air from a grill at the rear of the tunnel where the transmission disconnect/adjustment is. The gas heater was discontinued and that grill became a solid panel, then eventually the solid panel was covered with a carpet -- and you don't know it is there until you have to figure out how to disconnect the transmission shift rod to remove the engine..

I obtained an original grill, cut open the carpet, and use that air path as a second return to the evaporator in the smuggler's box. Don't know whether it adds much, but with a 911 A/C, every little bit helps.

I believe that hose goes to all of your vents. The triangle guy is the intake. Some here have mounted fans of it to increase air flow.

The round hole does indeed go to the center tunnel and there are air entry slots in the front sides of the tunnel under the carpet that provide alternate but limited return air paths. A separate nozzle on the top of the evaporator/blower housing attaches to the hose (flexible round ducting) leading to the dash cold air outlets.

Thanks for the replies! The transmission tunnel path is what I was referring to. I'm amazed at the poor supply to the evaporator from these two intakes. Any harm in removing the "bi-metallic switch" that makes for a significant obstruction in that path? Ant benefit in getting more air to the tunnel path?
Thanks again.

For moving more air thru the tunnel, I've thought about putting a small fan to blow INTO the tunnel at the rear. This would be similar in concept to putting a fan in the OTHER return to help flows there (thanks to Jim Sims, I believe [actually mthomas58 -- see next reply]). I have wondered how much improvement it would provide thru the restricted flow path in the tunnel. It stands to reason that the tunnel path would be a distant second to the floorboard path in mass flow of air, even with a fan assisting the tunnel path.

Here is what I did.......... not sure if there is any real performance benefit. However better airflow through congested/restricted footwell area cannot hurt!

Footwell fan thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/336402-evap-assist-fan-install-floorboard.html?highlight=assist+fan



http://forums.pelicanparts.com/uploa...1185976031.jpg

I later moved this 4" Spal puller (124 CFM) to the rear condenser (per my orig plan) and replaced the floorboard fan with a computer fan that moves 85 CFM and cannot be heard in the cabin like the spal.

http://forums.pelicanparts.com/uploa...1185977185.jpg

IIRC, these 3 fans move a total of 877 CFM. In my application, the airbox horn was removed to accomodate the 7.5" fan. The middle fan is 5" and just clears the Alt fan housing and the 4" fan just clears the heater duct. Unlike the footwell fan, I believe the condenser fans significantly help to to keep vent temps down, particularly in stop and go traffic.

Condenser fan thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/312760-adding-3-fans-rear-c-condenser.html?highlight=assist+fan

Thanks Mark, the small fan in the floorboard is a very, nice clean installation. I now realize (after searching Jim Sims' posts) that the resisters in the floorboard intake are for the three speed fan and I don't want to lose that function. From yours and others posts, sounds like I would be better off spending time and $ working on a rear condenser fan. Thanks again.

www.retroair.com sells an updated blower motor for cars through 85 (I think) that does not require the resistor pack.