Table of Contents
Advertisement
GM COACH MAINTENANCE MANUAL
Sec. 3
Page 41
Water modulation valve, connected into heater
lines and mounted in top of forward baggage com-
partment between heater blowers.
High temperature
overrule
thermostat and
water modulation valve Grad-U-Stat (thermostati-
cally operated air pressure control valve)which are
mounted on floor under fourth seat from front on
right-hand side.
Driver's heater, located behind grille in center
of dash panel, which includes a heater core, blower,
and a manually adjusted thermostatic control valve.
Two windshield defroster blowers, located be-
low windshield ledge.
Heating switch and driver's heater rheostat
switch, located on control panel at left of driver,
and defroster switch located on switch panel in
front of driver.
Two heater motor magnetic switches and two
automatic reset type circuit breakers, mounted in
forward
baggage
compartment
between
heater
blowers.
Hot water supply and return pipes, shut-off
valves, and electrical wiring.
OPERATION
Water Circulation (Fig. 10)
Hot water from
the engine cooling system is
forced through the heater supply line by the en-
gine water pump.
Actual flow of water through
the under floor heater cores is controlled by the
modulation valve, and flow of water through the
driver's heater core is controlled by the manually
adjusted thermostatic control valve. Water modu-
lation valve is air-operated, the air pressure de-
livered to
it
being graduated by the Grad-U-Stat,
which is sensitive to inside coach temperature.
After circulating through heater cores, water flows
through the return line to the suction side of the
engine water pump. Two gate valves, one in supply
line and one in return line, provide means of iso-
lating the heating system from the engine cooling
system for summer operation, or to permit work-
ing on either system without draining the other.
Valves are located in battery compartment.
Air Circulation (Fig. 10)
Under floor heater blowers run continuously
at constant speed when "HEATING" switch is turned
on. Blowers draw air through grilles in aisle side
risers and force it through heater cores into the
hot air ducts. Hot air outlet under each double
seat, except second seat from front on each side,
directs hot air outward and toward front of ve-
hicle. If for any reason inside coach temperature
continues to rise above normal thermostat setting,
high temperature overrule thermostat will open at
85°F, breaking circuit and stopping heater blower
motors.
Air forced through under floor heater
BODY
cores is entirely recirculated air, these heaters
having no outside air intake; air forced through
driver's heater core may be all recirculated air
or part outside air as desired through manual
positioning of dash ventilator.
Driver's heater
fan speed is controlled by "DRIVER'S HEATER"
rheostat switch on control panel at left of driver.
Refer to "Heating and Ventilation Wiring Diagram"
in back of manual for wiring circuits.
MAINTENANCE
General
1. Two oil cups are provided at each under
floor heater motor, accessible inside of front bag-
gage compartment, and one oil cup on extension
tube, accessible through dash safety compartment,
provides means of lubricating driver's heater fan.
These points should be lubricated periodically ,
referring to LUBRICATION (SEC. 13) for recom-
mended intervals and type of lubricant.
2. Heating system should be flushed semi-
annually, following same gene-ral procedure des-
cribed for
flushing
engine
cooling system in
"COOLING SYSTEM - GENERAi/' (SEC. 6).
3. At beginning of heating season, examine
heater pipe joints and fittings, and heater cores
for leakage and make the necessary repairs. Clean
all dirt from heater cores.
4. Check for
proper
operation
of
heater
motors, thermostat, Grad-U-Stat, water modulation
valve, and magnetic switches at b~ginning of each
heating season.
5. Drain cock is provided for draining mois-
ture from Grad- U -Stat and pressure regulating valve
air lines. Drain cock, located in forward baggage
compartment, should be opened at regular intervals
to eject moisture.
Draining (Fig. 10)
1. If heating system is to be drained without
draining engine cooling system, close two gate
valves in battery compartment.
2. Open vent cocks on under floor heater
cores; vent cocks are installed on extension tubes
in front baggage compartment, one at each side
of vehicle.
3. Open two drain cocks in front baggage com-
partment, providing suitable container to catch
drainage. One drain cock is located in bottom of
heater supply pipe, just to right of water modu-
lation valve; the other drain cock is installed on
extension tube at left of water modulation valve.
4. Open two drain cocks in driver's heater
lines, located under· vehicle near left front spring
just rearward of front axle.
Bleeding (Fig. 10)
Whenever engine cooling and coach heating
system has been drained and refilled, when system
Advertisement
Table of Contents
