Air conditioner/Heater intermittent

Problem: The air conditioner will put out hot air about half the time and the heater will put out cold air half the time. So we really don't have much congrol except on or off.

We refilled the coolent and when the AC is working it is very cold so that isn't an issue. We replaced the relay but no change.

It seems the actual movement of the car affects the change. I will have the AC on and if I stop a little hard or pull away from the stop sign a little too quick I will hear a "clunk" from inside the vents and it will start blowing out hot air. Also sometimes when it's cold and I want hot air, I will turn on the heater and it will blow cold air even when the engine has heated up.

So I guess I will have to have a mechanic fix it but it would be helpful if someone maybe had an idea of what it is that is causing these issues.

Any help would be appreciated.

Thank you,
Mike Divine