GMC PD-4103 Maintenance Manual page 46

GM COACH MAINTENANCE MANUAL
SEC. 3
Page 42E
temperature overrule thermostat and the "HEAT-
ING" switch on control panel at left of driver.
When "HEATING" switch is turned on, circuit
through magnetic switch windings is completed,
causing magnetic switch contacts to close. With
magn~tic switch contacts closed, circuit is com-
pleted to heater motors direct from battery junc-
tion. One 30 amp automatic reset type circuit
breaker is connected in series in each circuit
from magnetic switches to motors. Circuit from
"HEATING" switch to magnetic switch windings
is protected by Number 18 circuit breaker on
circuit breaker panel at left of driver.
Magnetic switches are sealed units and are
not adjustable or reparable.
If
either switch fails
to operate, it must be replaced. Before replacing
switch, check circuit continuity through circuit
breaker to make sure the trouble is in the switch
and not in the circuit breaker.
DRIVER'S HEATER (FIG. 10)
Driver's heater unit, consisting of a heater
core, motor, and a belt driven fan, is installed
in center of dash compartment. Push button type
bleed valve is located in top of heater core out-
let pipe at upper right-hand corner of core. Flow
of water through heater core is modulated by reg-
ulator valve connected in heater core outlet line.
Regulator valve is mounted on side of dash com-
partment panel at right of driver. Regulator valve
capillary tube samples air in coach, causing valve
to reduce or shut off flow of water as coach
temperature rises to the desired setting.
Manual adjustment of regulator valve is pro-
vided by a knob installed on valve shaft. Turning
knob clockwise raises regulator setting, and com-
plete clockwise rotation (past detent pressure)
holds valve fully open, regardless of coach temper-
ature. Turning knob counterclockwise lowers regu-
lator setting, and complete counterclockwise ro-
tation holds valve closed, regardless of coach
temperature.
Air forced through heater core may be all re-
circulated air, taken in through dash compartment
grilled door, or part outside air taken in through
dash ventilator. Dash ventilator may be opened
or closed by driver by turning ventilator control
knob, accessible inside dash compartment. Speed
of heater fan is controlled by "DRIVER'S HEATER"
rheostat switch on control panel at left of driver.
Heater unit mounting bolts are accessible after
opening dash compartment door, and after re -
moving front license plate holder from outside
vehicle. Heater water line connections are also
accessible through front license plate holder open-
ing.
WINDSIDELD DEFROSTERS
Dual windshield defroster blowers are mounted
under windshield ledge. Motors are non-reparable
BODY
type, and should be replaced in event of failure.
Defroster blowers are controlled by three-
position "DEFROSTER" switch on switch panel in
front of driver. Defroster motor circuit is pro-
tected by number 19 circuit breaker on circuit
breaker panel at left of driver.
VENTILATION
Outside air can be admitted to coach through
adjustable dash ventilator in front panel, through
hinged section of driver's window and front en-
trance door window, and through sliding half of
each side window sash.
In addition, two motor driven outside air blow-
ers, mounted in roof at forward end of each pack-
age rack, draw in outside air and force it through
ducts into interior of coach. With all other open-
ings closed, blowers slightly pressurize coach
interior, thereby serving to exclude unconditioned,
air, dust, fumes, and moisture from coach. Air
is exhausted from coach through louvered opening
in bottom of entrance door.
DASH VENTILATOR
Dash ventilator requires little maintenance ex-
cept for periodic inspection of seal and screen.
Open ventilator and inspect seal from outside
coach. Visual inspection should disclose defective
seal; however, seal can be effectively tested with
a water hose. Replace defective seal, using a
good grade of cement for attachment. Inset in
figure 1 illustrates ventilator, seal, and control
knob installation. Clean screen with compressed
air, blowing air outward from inside vehicle.
OUTSIDE AIR BLOWERS
Blower and motor is mounted inside housing
at front end of each package rack. Intake grilles
on sides of roof admit air which blowers force
rearward through ducts. Air flow reverses in
compartment in rear end of roof, flowing forward
through distributing ducts. Slots in ducts above
side windows distribute air to interior of coach.
When coach is equipped with air conditioning, com-
partment at rear end of roof houses the cooling
evaporator, which dehumidifies and cools the air.
Blower Operation
Blowers are controlled by rheostat type
"BLOWER" switch on control panel at left of
driver. Switch permits driver to shut off blowers
or vary blower speed as desired. However, when
air conditioning is used, blowers operate constantly
at full speed when "MASTER SWITCH" is in
"COOLING" position, and "BLOWER" switch is
inoperative.
Blower circuit, fed through "RUN" position of
diesel "CONTROL" switch, energizes blower relay.