Is it possible to just remove the thermostat so that the flow of water will be cold always? What is the right procedure?

you said it only overheats or runs hot when the ac is on right?

yes it only overheats when AC is turned on.

did you clean out the fins of radiator and condensor???

yes the whole radiator was cleaned .

the condensor too? this will restrict the air flow that is needed for cooling.

if you have cleaned the radiator and condensor externally then you may have an issue with the ac system. Sounds like the condensor is gettin too hot and may be overcharged or a restriction causing the pressure to get too high on the high side. You would need guages hooked up to high and low sides to see pressures. Did you add any freon to the system?

AC is very good and cold. Another observation I saw is that the container which is used to refill the coolant is always at low level when overheating is happening thereby i have to refill it again.

The coolant reservoir is low when overheating is experience so i have to refill it again.

did you got it fix