I have a 98 F150 2wd 6cyl that overheats everytime the air is on. I have replaced the thermostat, and the water pump is fine. There are no leaks at all. As soon as I turn the air off, the gauge goes back to normal. Any one out there have any ideas of what it could be.
Thanks

 

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is the air cooling like it should?have you flushed the coolant system?the radiator could be restricted.aslo look between the ac condencer and the radiator and see if you have debrise over the radiator.

 

Does the engine temp slowly rise or is it all of a sudden as you engage the AC? Have you thoroughly cleaned the radiator the condensor and the space between them? Is your clutch fan working and not slipping?