Less power at switch-on air conditioning!

Hello! I drive a Toyota Picnic turbodiesel. For over 2 years I have had the following problem: When I turn on the air conditioner my Picnic goes down immediately with the power. If I turn the blower to the highest power, then I hear that the ventilation wheel rotates faster and more slowly. I also notice this when I step on the clutch, but the air conditioner is switched off! I also noticed at night that when the dome the light is getting a little weaker. If I stay on the clutch, the ventilation wheel turns slower at the moment, then it’s normal again. But I really have the biggest problem with the air conditioning switched on. If I also set the blower to the highest performance, it can happen that the car “rupts”. Of course I was already in some workshops! The first car workshop told me that the air conditioning had to be renewed. The second said that a new alternator would be installed. The next one said that the clutch was defective (but it was renewed about half a year ago). Another workshop told me that the gearbox was broken!!! The last workshop I visited actually meant that the summer didn’t last much longer anyway and I didn’t need the air conditioning anyway in the winter!!! So, now I hope that some specialists in this forum will be able to help me!!?? Thank you very much!!