GMC 1976 ZEO 6083 Maintenance Manual page 765

phere, discharges it into the combustion chamber,
and forces the combustion products out the exhaust
tube . The circulating room-air blower pulls return
air in and forces it across the heat chamber, discharg-
ing into the area to be heated .
LIMIT SWITCH (FIGURE 3)
The limit switch will open if the combustion
chamber temperature gets hotter than normal oper-
ating temperature. Referring to Figure 2, if HTL
(high temperature limit) limit switch opens, this
shuts off current flow to the blower switch and re-
sults in closing of the gas valve.
A centrifugally operated switch is located inside
blower and controls the opening and closing of the
gas (solenoid) valve.
GAS VALVE (FIGURE 4)
The gas (solenoid) valve controls the flow of LP
gas to the burner assembly .
IGNITION PAK (FIGURE 4)
The ignition pak is basically a step-up trans-
former that builds up the 12-volt input to approxi-
mately 20,000 volts. This voltage is supplied through
a high-tension lead to the spark electrode whenever
the thermostat contacts are closed (calling for heat).
BURNER ASSEMBLY (FIGURE 4)
The burner assembly contains LP gas spray noz-
zle, the spark electrode, and a air adjustment feature
(See "Primary Air Adjustment" later in this section) .
The spark electrode will supply a constant wiring to
ground through the burner assembly whenever volt-
age is supplied from the ignition pak .
Figure 4-Furnace Components (Right-Side)
Figure 5-Manual Valve and View Port
FLAME ROD (FIGURE 4)
STARTING FURNACE
FURNACE
24G-3
The flame rod is a switch which closes when the
combustion chamber reaches a specified tempera-
ture . When the switch closes current is supplied to
the coil of control relay 3CR and therby shuts off
current flow to the thermal relay heater TH 1 (See
figure 2) as the normally closed contacts 3CR are
opened.
OPERATION
1 . Turn thermostat to "OFF" position .
2. Open LP gas tank valve.
3. Open manual furnace valve (figure 5) .
4. Press manual reset button on furnace (figure
5 . Turn thermostat (figure 7) to a temperature
above room temperature. Furnace should start.