There's an equivalent effect when lining up for takeoff that the cabin air conditioning goes off (if it's a noisy one you hear it stop). This is to ensure all engine power is available for takeoff, particularly if engine failure procedures are suddenly required. Cabin air conditioning draws a surprising amount of the engine power. The AC comes back on during the climbout. The same is done on final approach in case the crew have to make a sudden full power go-around.