Heater controls ticking

The heater in my truck only works on high. I have changed the blower motor and controls, and still only high works. Behind the glovebox on top of the plenum are three black boxes (relays?) with the purple wire (power) heading directly to the motor. When I change fan speeds they click really loud, is this normal? There is no power to the motor at low and medium speeds. They all have the same part number also is this correct, or should they be different?