I have whirlpool split ac the fan in outdoor unit spins very fast in any mode?

i have recently bought whirlpool aviator ac .the fan in the outdoor units spins in high speed only in any mode changed but indoor fan speed varies .isn't it fault or all the air conditioner outdoor unit fans will spin in only high speed only.please help. as the installation fellows gave wrong connection by phase in neytral and neutral in phase when installing now it has been rectified .