Hi:

Out truck is a 73 C900 with a 477 motor. On the back of the motor there is a canister where some air brake antifreeze can be added. As the compressor runs, it draws in some antifreeze and this antifreeze air mixture prevents the brakes from freezing. Another option is to add an air brake dryer similar to what can be found at Meritor WABCO -- Products -- System Saver Air Dryers but given where you live you may not frequently need this item.

PaMnd