AC kabhi kabhi garam hawa detahe, code 20 in FATC 

ac some time not working . In this time when ac not working fatc [ Fully AutomaticTemperature Control System] code generate 20. Which means temperature control actuator faulty.
This actuator control heat and cold air mixing when we control heat in fatc module the actuator open or close the flap and perfect temperature come in cabin.
so wwhen actuator not send feedback massage fatc not know how much % door is open.
I replace this actuator against code 20 and problem solve.