Is it ?
If mine is set to "auto" then the climate control decides whether to use air con or just the heater. and if I manually switch off it stays off if manually switched on it will come on on next start up
Either way the engine needs to be running so that the compressor can operate the heat exchanger. The fan is electric of course but this only moves the air around hot or cold.
Make sure you do not leave the air con off for long periods of time else with disuse the seals dry out its cheaper in the long run to use it regularly even in the cold weather it will demist windows faster.