Meg2 engine speed drop when heater turned on

Hi i've had a quick search but could not find anything.



So when i have my foot on the accelerator and increase rpm to 1400, then turn on the fan/heater to full, i hear a click from the glove box and a second later it drops to 1200 rpm. The opposite is when i then turn off the fan, i hear a click but it take 4 seconds to then speed up.



I've only noticed this the other day is it normal??