Overheats when AC on

How high the temperature get? During the summer, with the A/C running, it is pretty normal for the temperature gauge to rise a little bit.

If it is going up more than just a shade or two, then start with checking the coolant level when the engine is cold enough. If it is low on coolant, then you have a leak that needs to be addressed. Let us know and we will go from there.

Ok. Again, how high is the temperature going? Going up just a shade or two is normal. If it's going much higher than that, or overheating, then there is some sort of issue. Perhaps the system just needs to be flushed. Or maybe the thermostat isn't opening all the way. Maybe the radiator core is clogged up with gunk.

I would suggest taking a good look at the radiator core to see if it has a bunch of dirt on it. If it does, it's keeping the fan from being able to pull enough air through to cool the system. An easy way to fix this is to simply spray it with the water hose with a little bit of pressure.

If that's not the problem, then flush the cooling system. Here's a guide: https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

Let us know what you find.

Ok. Go ahead and clean that off of the radiator if you didn't already. Also make sure there isn't any on the AC condenser (the thing in front of the radiator). Change the thermostat and be sure to bleed the cooling system really well. Let us know.

Hmmm maybe the extra pressure of having the waterpump push coolant through the system is helping to open it some. Again, I suggest changing it. They sell them at AutoZone for less than $10.

Ok. Keep us posted