Thomas C2 School Bus Heating System


The heating system in the Thomas C2 conventional school bus is fairly modern with electrical controls that move using a dial type switch that is called a rheostat. A rheostat is a resistor that controls how much the motor turns to open and close a door in the heat ducting for cold and hot heating action. We have changed quite a few of these motors since they are a moving part. Moving parts eventually wear out and fail.

Other heating system parts that can fail is the coolant booster pump found on most school buses. It’s a circulation pump that helps the engine water pump push the coolant from one end of the bus to the other. There is one inch heater hose that runs to the back of the bus and returns to the engine. This is a substantial amount of hoses and coolant that has to circulate through the entire coolant system. If you consider other truck cooling components they do not have anything like a school bus set up particularily on this Freightliner model.

There are 3 sets of underseat heaters with two blower motors in each set. They draw a lot of amps which can put a high load on the breaker and switches. I have seen heater switches melt because of the heat that comes from heavy amperage going through the contacts. This usually means the blower motors are getting tired and drawing too much power than the circuit board can handle. The motors have to be replaced.

The heater box in the video also had a faulty heat control door. The linkage arm I showed you hooks up to this door and then to the heat control motor. Unfortunately the door arm was damaged so it had to be removed and repaired. JB Weld is an amazing product that repairs plastic. It’s an epoxy that mixes up in two parts that bonds well and hardens to a solid that is very durable. This stuff avoids waiting for costly parts and dealing with down time.

If we had to wait for parts this bus would be out of service because of the no heat problem in the driver’s cab area. Due to the winter conditions we could not let it back in to service. Comfort in a school bus is important and we can’t expect drivers and students to bite the bullet and freeze while on their way to school.