Engine Temp Goes Up (75%) when AC is on Auto but if its on circulation mode it goes back to normal no matter what the temperature settings. I had already the parts to replaced the radiator cap, engine temp sensor (2) and thermostat this coming Saturday. Anyone has experienced this?

 

That's dangerous with your aluminum heads/block.

I had a temperature issue on my 2G Legend that was much worse with A/C, and it turned out to be the thermostat getting stuck. That may not apply though.

 

That almost sounds like the system isn't generating enough pressure. In addition to all you've already ordered, when was your water pump replaced?

 

Have worked on MANY vehicle brands as a mechanic throughout my life .... but have very little shop time on Honda/Acura ... except Honda motorcycles.
With that said, I've never experienced a car that would come up to "normal temp" on the gauge as quick as the RL we just acquired.
I realize it's summertime in the south & hot as hell but my car is up to the normal temp on the gauge before I reach the end of the road that I live on & it's only 1/2 mile long.
Granted, it doesn't rise any farther than that while driving with a/c ON & I've been keeping an eye on the gauges, especially in town.
Anyway, in my experience in situations like yours, I'd be looking at possible electric fan failures & their sensors & air trapped in the cooling system on top of the things you're already preparing for.
The cooling fans on most cars are designed to come ON when the a/c does.

Good luck

 

^It actually didn't even occur to me until you said it, op check to see if the fan comes on when you turn a/c on. That might be what's happening too.

 

While we're here, the driver's side fan is for the radiator and the passenger's is for the A/C condenser.

 

Thank you all for the tips, I have completed replacing the thermostat, 2 temp sensors and as well the radiator cap. After completed i use lisle to burp the coolant for trap air. The car has been service for the timing belt as well the water pump, car now has 165k. I had the car running for 45 mins with the AC full blast at auto mode, outside temp is 81 degrees and the temp never move and stayed at 40%. Still early to tell need to test the car when it reaches 100 degrees on the weather here in LA. About the fan both kick in when the A/C is not on and turned off, When the A/C is on both fan still kick in. I had replaced the A/C condenser fan 2 months ago since its making a grinding sound.