Low coolant light when ac is on 323i

I have a 2000 323i just payed over 1k for a coolant leak not including that I changed the thermostat, pulley and reservoir.

When I turn on the car the ac works well once in a while but the low coolant light turns on seconds of ac working then sometimes when the car is off the fan starts working on its own. On and off periods

The heater doesn't work I didn't have money for the work so I had it looped I hope I get some insight please would really appreciate it...