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My car makes no difference AC on or off, the only difference is when it's like 85º outside and I have the A/C on, and my coolant temp hasn't reached 190º yet, so my manual fan switch hasn't kicked the fans on, and the A/C kicks em on..the coolant temp will drop to 180º.
With no manual fan switches the car will run hotter with a/c on because you usually have the fans on already........then the hot air from the condenser adds to the heat ..........on the interstate or open road it should not be a problem.
If you DON'T have the manual switches (or if they aren't turned on) then the heat gets up there and the a/c when turned on turns the fans on...... hence the cooling effect..........
BTW don't forget about the debris in between the rad and condenser :yesnod: