2 questions regarding air conditioning control

[gnomegemini 7]

Hi there,

 

the POH states not implemented but the cabin heater master switch indeed does some things: you can heat up the cabin but even when only battery connected. So my question is: is this switch the cabin heater which uses fuel or is this the master switch for cabin heating? As far as I understood the manuals the cabin is heaten up by air warmed by the engines and there's an alternate fuel using cabin heater which uses fuel from No 2 main.

 

The second question is: what is the Aux Blower switch right of the magneto switches. The POH page 27 even does not have this switch in the picture.

 

Thanks in advance.

[downscc 1,327]

The heater switch is for the fuel burner.  I simply don't know the answer to your aux blower question.

[gnomegemini 7]

The heater switch is for the fuel burner.  I simply don't know the answer to your aux blower question.

Then why is the cabin temp decreasing when I switch it off while in cruise and cabin supercharger are hot? If it's the case it should be heat the cabin but instead it's going to off.

[gnomegemini 7]

*Push* (sry for that).

 

Maybe someone can clarify on this? I'm wondering if the cabin heat switch would be the supercharger for cabin heat because normally in flight warm cabin air should get mixed with air warmed by engines. Even if it'll be Kyle pointing me to the right RTFM page would be much appreciated. Also the correct work or use of the aux blower (what's this? When to use?). I'm really interested in understanding the technology behind.

[downscc 1,327]

I didn't understand your question.  The air conditioning section in the POH has a brief overview on pg 138 but not much detail.  Basically, the air is heated by the supercharger providing the pressurized air, not the engines directly, and there is an air cycle turbine available to cool the air same as bleed in a jet is cooled. There are two cabin supercharges one on each inboard engine. However, over Labrador at night you need more heat than the superchargers provide so there is a fuel burning heater to help out.

 

Air cycle cooling is basically passing hot compressed air through a turbine, the air looses heat by turning the turbine and expanding enough to provide cool air.

[gnomegemini 7]

Ah ok. I thought the cabin heater switch is not for the fuel burner but the main switch for the superchargers in the cabin as no fuel is consumed and even in cruise when switched off you don't have a working AC.

 

My understanding of the AC is even when fuel burning heater is switched off, you should have at least in cruise a working AC. However when I switch off the cabin heater switch, the whole AC is switched off as you can see on the cabin temp mix valve position (which goes to full cold) and temp get's lower until reaching 50°F.

[downscc 1,327]

Maybe we're not communicating.  When I refer to cooling I imply AC, which is provided by the cooling turbine (switch is index 245 page 33 POH). If you turn of the fueled heater, which is the normal mode of operating, heat is provided by the pressurized air and cooled by the mix valve which blends the warm pressurized air with the cooled air from the cooling turbine.  Operation of the mix valve is on pg 138 POH.