LincTex wrote:
All airliners basicly use a freon sytem (seldom) or "air
cycle" packs. (common)

Air packs are simple and light, but use a LOT of fuel to operate.
Freon systems are MUCH heavier and more complex, but more efficient.

If you have been on a long flight several hours you will notice the
aircraft get very warm inside. This is because the bleed air is shut
off from the air packs to save fuel. Some airlines pay the pilots
additional salary if they save fuel. This is why many airlines don't
start all the engines until they are at the end of the taxiway. Fuel
is money bleed air costs fuel, cool air cost money.

Stache