92 caravan 3.3 Coolant Overflow

For the last year or so i notice that in the summer time and when i run my air conditioning and do a little idling when i shut the van off the coolant in the overflow bottle rises a little and bubbles for about a minute. I am not sure how long its been doing this is it normal. It really only does it when i use the AC. It never bubbles when the engine is on only right when i turn it off for about a minute. Is this normal. What could be causing this?

Usually when you run your engine with yourt ac on you are putting more load on your motor so it works harder and will want to run a little hotter. when you shut off your motor it will typically overflow into your overflow tank and then as your motor cools it will draw the over flowed coolant back into the radiator. This is normal as long as your temperature on your gauge stays within the normal operating range which is around half way on the gauge.