GMC 1976 ZEO 6083 Maintenance Manual page 766

24G- 4 FURNACE
Figure 6-Location of Reset Button and Fuse
NOTE :
A rumbling or growling noise is not nor-
mal. Refer to "Primary Air Adjustment" later in
this section.
6. Set thermostat to desired temperature and it
will cycle the furnace on and off as the temperature
inside the MotorHome satisfies the thermostat .
SHUTTING OFF FURNACE
1 . To shut off furnace set thermostat to "OFF"
(See figure 7) .
2. Close furnace manual valve (See figure 5) .
SEQUENCE OF OPERATION
THERMOSTAT CONTACTS CLOSE,
CALLING FOR HEAT (START CYCLE)
1 . Control relay 2CR is energized providing
power to the ignition pak, thermal relay heater,
blower motor, and control relay 1CR. When control
relay 1 CR is energized power is supplied to the aux-
iliary furnace blower, through terminal 1 on the con-
trol box.
2. When the blower reaches minimum operating
speed (approximately 2-3 seconds), the blower
Figure 7 -Furnace Thermostat
switch contacts close providing power to the gas (so-
lenoid) valve.
BURNER IGNITES (START CYCLE)
1 . Approximately 10-15 seconds after ignition the
flame rod (switch) contacts close, de-energizing the
thermal relay heater TH 1 through control relay
3CR. The furnace will continue running until the
thermostat is satisfied and its contacts open .
THERMOSTAT CONTACTS OPEN
(PURGE CYCLE)
1 . The coil of control relay 2CR is de-energized,
stopping the flow of power to the ignition pak and
the gas valve. Power is maintained to the blower
motor through the still closed 3CR contacts.
2. After approximately two minutes the flame
switch cools, opening the circuit to control relay
3CR and de-energizing the blower motor. This also
opens control relay 1 CR contacts and de-energizes
the auxiliary furnace blower .