Coach heating continued

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

COACH HEATING

In most cases, coaches are “comfort” heated by way of hot water, forced air system, utilizing circulated coolant.  Heated coolant, generated by the combustion process, is circulated through the system.  Fresh and re-circulated air is used to heat the interior of the coach.

Hot water is forced through the heater supply line by the engine water pump. An electric water circulating pump and motor assembly pushes the coolant through the main heater core supply line and the driver’s heater supply line.  In some cases there might be an optional sidewall heater supply line.

Gate valves, one in the heater supply line and one in the return line, provides a means of isolating the heating system from the engine coolant system. This allows for one system to be drained while the other stays intact.

Once the coolant circulates through the main heater core, the driver’s heater core, and any sidewall heating lines, it is returned to the thermostat housing on the engine by way of the heater system return lines.

Most of the components are the same regardless of the coach system.  Each system has a heater core.  It is made of a fin and tube design, much like a radiator. Warm water from the engine circulates through the tubes of the heater and provides the means of heating the air forced through the system by the blower motors.

The blower motor portion of the system consists of motors and blower fan wheels. Each blower motor draws outside air through a filter screen into the heating and air conditioning compartment.  The driver’s compartment has its own blower motor, separate from the main motors.

A hot water valve assembly is included in each type of system as well. Some have a water modulator valve which is air operated. This valve is a spring loaded, piston type valve. Movement of the piston actuates the valve’s stem, opening and closing the valve. In other coaches, there is a solenoid water valve. It is electrically operated but performs the same function. This valve is normally closed but when energized to open, it controls the flow of coolant as dictated by the heat control circuit.

In older coaches, there may be a grad-u-stat.  This is a thermostatically air controlled valve that is sensitive to the inside coach temperature. Expansion and contraction of the element of the valve is caused by the increase or decrease in the coach temperature.

Every type of system requires some type of temperature control assembly. Some controls,  which are used, are electrically connected to the air operated main valve in the system and the temperature probe which is installed in the coach’s duct.  For more mature coaches, these controls are connected to the grad-u-stat which has a temperature range of 65 to 85 degrees.

All systems have a water circulation system that works in conjunction with an air circulation system.  Both systems need to be in full operating condition in order for the heating system to work at its optimal capacity. 

This blog is for informational purposes only. All information provided herein is not intended to take the place of a qualified mechanic, when deemed necessary. 

Sources: GMC 4108-4905, RTS, and MCI manuals