Coolant reservoir bubbling over when A/C is on

Hello, I've changed the water pump, thermostat, and refilled it with Dex coolant. I have hot air coming out of the heater. I have A/C that works. Problem is that when I'm driving the car and I have the A/C on for a little bit the coolant reservoir begins to bubble over. And by that I mean it looks like it's in a rapid boil. However it is not boiling or overheating just bubbling over rapidly. And the coolant is coming from the drain hole on the bottom of the reservoir. I did several heat and cool down cycles to try to get the air bubbles out. I burped the hoses several times. I thought I had all the bubbles out, air pockets, air out of the system. So three times now that I did this and several bottles of coolant later I'm still having this problem. Also I should note that the car usually runs on the first increment under 225 which I'm guessing is approximately 200°, just fine and so far it only does this when the A/C is on. It will run at this temperature with the A/C off and there's no problem, turn the A/C on and at the same temperature didn't because the bubble over but according to the gauge it's not overheated. Any help or advice you have will be greatly appreciated. Thank you for your time.