Two systems, using forced air, are used to heat the interior of the coach. One is the defrost heater which is used to heat the front of the coach and the driver's area. The other is the underfloor system that uses the evaporator core, heater core and air filter screen in conjunction with blower motors for circulation.
Hot water from the engine cooling system is circulated through the supply lines, using the water booster pump, to the heater core. The "Heat - Air Cond." control switch and temperature range switch control the flow of water through the coil of the front heater core. The heater control valve increases or decreases the flow of water through the defrost heater core. After going through the heater core, the water is returned to the engine via a return line.
Gate valves, which are located in the heater supply and the return lines, provide a way of isolating the heating system from the engine cooling system. This allows for one system to be drained while leaving the other system intact and undisturbed.
Draining of the heating system is accomplished by the use of a drain cock which are located in the front heater system supply and return lines. Additionally another drain cock is located in the front heater core which is used to drain the front heater core and lines.
In addition to water circulation, adequate air circulation is also required for the system to work properly. Blower motors, in the heating/air conditioning compartment, draw some air from the outside, through a filter screen. Air that is recirculated is also drawn into the same compartment by way of ducts that are located under the seats (return air).
The blower motors draw the blended air through the heater core, evaporator core and filter screens. It is pushed into the coach interior. When the "Heat - Air Cond." switch is in the "Heat" position, the blended air is not affected by the evaporator but heats up as it passes through the heater core.
The heated air enters the coach through ducts that are on each side of the coach at the floor and directly adjacent the windows. The heat warms the floor and the feet of the passengers. Ducts along the left side of the driver's area, warm the driver through adjustable vents.
The defroster heater assembly performs two functions. The first is that the heat is used to keep the windshield defrosted. It also recirculates air to provide heat to the front of the coach. The front heater core warms recirculated air that has been drawn through the dash compartment opening by the front blower motors.
The engine water pump and circulating pump motors use the pumps to provide water circulation to the main heater core, the driver's heater and sidewall heaters. In some cases there are also return air shutters which are used to control the recirculated air and outside air.
This blog is for informational purposes only. It is not meant to take the place of a qualified mechanic when one is deemed necessary.
Sources: MCI 102D, GMC 4108-4905, RTS06
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