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ECS: Manual A/C fan speed behaviour

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Ref. Quick start guide 4.11 Environmental Control System

Airframe located in ambient temperature of -20 deg C. Temp knob set to max. Door closed, idle flight mode. Cabin temp at -19 when AC set to manual mode. Bleed in auto. Hot air flow in mid position. Pres mode auto, dump in norm.

When AC in manual, cabin temperature increase when fan speed is set to off - and decrease if fan speed set to 1 through 4 - decreasing faster at setting 4. When AC set to auto, cabin temp increase.

Normal behavior?


Windows 10.0 (build 17134/2)

X-Plane 11.26r2 (build 112601 64-bit)

TBM900 1.1


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i have seen some similar: In Mode AUTO -> everything is fine.

In Mode Manual:

- Teste at ground with engine in idle


With further testing i saw, this behaviour is depending on the outside temperature.

So we might don´t have a "cooling", we just might have not enough heat power. This seems to be the reason for the temperature drop on higher fan levels.


In this diagram:

AirCond was off

@ 8:00:  set temperature to 20°C, FAN = 4

@ 7:30: FAN = 2 (here the AC holds temperature)

@ 5:25: FAN = 4 (drop to missing heat power)??

@3:50: increase of outside temperature from 13°C to 21°C


So, maybe only FAN-4 is a little bit too strong?

But i wonder, even with increasing engine power to 90% torque, i get not more heat power??


In the weekend i will do some more testing in the air.



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Thanks for your comment. Interesting graph, will also do more testing during the weekend and post some curves.

In my described scenario I had -19 deg. C in cockpit and had the AC in auto as usual when fiddling with the flight planner. After the G1000 hacking were done I registered the cabin temp had risen to +10C, and since the 'pilot' still had 'blue' vision due to frost, i tried to boost the cabin temp in manual mode. But alas, any fan setting, other than "off", made the temperature plummet. Turning AC to auto made the temperature rise at a steady rate - similar to when AC in manual had the fan turned off.

Found this to be a bit strange, but I've never been in a TBM in the Arctic before.

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me again ;)


i think i found the "room for improvement":

In flight, -36°C OAT, IAT setpoint 21°C.




just switching AC = MANUAL:



Vapor system active with full cooling power in manual mode.

So my first assumption should be corrected. We don't reach the temperature due to missing heat power, it seems we heat and cool at the same time, instead of just heating at this temperatures.


But i think, this is now a task for the developers ;)


Anyway, i´m still excited from the aircraft. Such a complex air conditioning system.

Many other designer implement just slow ramp to setpoint temperature


I would have done more testing, but a CTD again killed my flight




Edited by Martin_1970

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just some additional informations:

I had a look in the POH, section 7.9 of the real aircraft. 

Compared to the model , the implementation of the FAN, just adding more fresh (and maybe cold) air, is correct.


But the real aircraft has a control for the evaporator (parts 20, 22), which is not implemented in the model:



So, finally: If you don´t want to freeze, stay on automatic mode :D



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Aha. Two separate air flow systems. The diagram clearly show that the fans pulls ambient air through the evaporator in a cooling loop, regulated by thermostatic valves. The second loop is for the generated hot air, flowing through a mixing ejector. It is a fairly simple, but robust system and it makes perfect sense now.

Thank you for the reference to the pilot handbook.



Edited by Beef

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