Overheating with AirCon ON, OK with Aircon OFF

Could be a blocked radiator internal or external, or a faulty viscous fan hub..

Check fan hub has resistance to turn..

Check radiator for debris..

bubbling when the coolant is full indicates a head gasket problem. have a compression test done to check for gasket/cracked head. have a flow test done on the radiator as the cores may be blocked reducing coolant flow.

are you referring to the engine temperature overheating or the cabin temp not cooling down with the aircon on? I am struggling to think of a reason why operating the aircon would affect engine temperature

Full coolant level does not mean your engine cannot overheat. You need to fix the problem as overheating will destroy the engine if not addressed.

The radiator cooling fans must be working, as must the water pump. The thermostat must also be working properly.
There must also be no air in the cooling system as air locks will impair water flow. When cooling systems are drained fully or partially and re-filled air in the system must be bled out using the correct bleeding procedure for the particular engine/cooling system. Failure to do this properly will lead to overheating.

If you ONLY see the overheating warning when running your aircon you need to check that the electric radaitor fans are kicking in at idle when you switch on and run the aircon and the engine has been warmed up some. If they do not start operating when the a/c is running you will get an overheating condition in normal driving conditions.

If the radiator fans are operating normally and you still get an overheating warning when the aircon is on or off the most likely culprit is a faulty thermostat in the engine's cooling system which will need to be replaced.

If you have either a faulty thermostat or if the water pump in the cooling system fails you will get continuous overheating whether the aircon is on or off.

1. check if your water pump is is working.
2. check if it is not overheating when the A/C is off. if it is no longer overheating, have your a/c compressor checked by an aircon technician

The cooling fan should run continuously when the A/C is on. If it does then I suggest you drain and flush the cooling system, and replace the thermostat. Fill it with a fresh supply of a 50/50 mix of antifreeze and distilled water.

sounds like the blower motor resistor is bad. Just a guess

You need to check youe water pump, thermostat and your radiator cap and if all of that is good it sounds like a blown headgasket.

Are you sure you are seeing engine oil or is it coolant??
Chances are that it is coolant and that when you use the AC the engine is overheating. Do you have a temperature gauge on that car to indicate the engine temperature??.
Make sure your radiator fans are working--when you turn the AC on the fan at the back of the radiator should come on.

There may dirt or rust in idle air passes
Service & adjust the Idle speed control valve & throttle position sensor.