Grant:
I was out flying today; OAT was 27F. I had hot air coming in the cabin, and hot air coming out the defrost, cabin air off, but my feet were frozen. I checked the archives on BAC because I remembered reading something about cabin heat. I found a posting saying to leave the cabin air on when trying to heat the cabin. Is this correct? It appears counterintuitive. If it is true, can anyone explain why?
Editor:
The Cabin Air control is there to completely shut off the air from the firewall-mounted heat/ventilation air valve and ducting, in the event of a firewall-forward fire. It is an “emergency control”, not normally operated on a routine basis. It’s normal position is usually “In” (open); it is placarded to “Pull Off”, meaning “pull to close”. The Cabin Heat control allows heated outside air to enter, as it is pulled (opened), assuming that the Cabin Air valve remains open (in). The Defrost control operates a diverter valve that selects between floor heat or windshield heat.
These are all controls that should operate smoothly, and should be checked and lubricated at each Annual, unless they have a Teflon tube liner (needs no lubrication). To my knowledge, none of the originals were the Teflon-tube style. Your valves may not all be working freely, if you still felt a noticeable heat flow from the defrost ducts with the Cabin Air control pulled out.