I have a 93 civic lx and my car just started to overheat after i did a tune up on the car. It will start to overheat when my air conditioning is on. If I turn off the air and just turn the temperature gauge to hot the motor will cool down to pretty much normal(This is without the blower motor blowing air, just turning the guage to hot). Any ideas

 

You should bleed the coolant. You could have an air pocket in there somewhere. It has happened to me before after flushing the radiator, I bled the coolant and it was fine

 

i doubt its the coolant ,unless you just flushed the system, if your AC is cold while your driving on the highway its def your radiator

 

your thermostat could be clogged or bad, give it a shot and look. worst case is since u did a tune up the water pump was installed wrong and /or is leaking.

 

my guess is the thermostat. $19 from honda.
or you could get a new radiator. id suggest Del sol Dual core or a Fluidyne.
It also could be your coolant. try bleeding the system