When I set up my non pressurized Lancair IV, I decided to use the bleed air from the intercoolers for heating the cabin.  I designed my own air mixer box to mix ram air with hot bleed air.  I talked to Ross at lancair about how to do it and he warned me that I should not ever let the bleed air be shut off without allowing it to go overboard.  He said that completely shutting off the bleed air could cause a compressor stall at high altitudes.

 

I designed an airbox that if my temp. control is all the way to cold the bleed air goes overboard.  Also if I shut off all air into the cabin the bleed air goes over board.  I have not had any problems with this system

 

Tom Byrnes Lancair IV N54TB