The A/C pump draws needed power from the engine. If you throttle your engine over 60% or so the vehicle has a system to stop the pump, This is done for two reasons, One is so that the engines power is entirely used for moving the vehicle. The other is to prevent damage to the pump from turning too fast.
If your blower motor stops as well this is because you have a fairly new vehicle and the A/C system is controlled by a computer, when the pump gets turned off on late model vehicles the computer also slowes the blower motor.
It does not actually stop it just slowes down.


