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SERVICING
Testing Auxiliary Limit Control
S-302 Checking Flame Rollout Switch
DRG units are equipped with a temperature-activated
manual reset control. This control is mounted to the
manifold assembly and is wired in series with the auxiliary
limit and gas valve. The control is designed to open should
a flame roll out occur. An over firing condition or flame
impingement on the heat shield can also cause the control
to open.
If the rollout control has opened, the circuit between the
ignition control and gas valve will be interrupted and the
ignition control module will go into lockout. The servicer
should reset the ignition control by opening and closing
the thermostat circuit. The servicer should look for the
ignitor glowing which indicates there is power to the
ignition control. The servicer should measure the voltage
between each side of the rollout control and ground while
the ignition control is try to power the gas valve.
Checking Flame Rollout Switch
Limit Switch Operation (Applies to Primary, Auxiliary,
and Roll Out Limits) DSI systems.
If a limit switch opens, the indoor blower is energized on
heat speed and the induced draft blower is energized. The
LED on the control flashes “4” to indicate an open limit
switch. The blower and inducer remain on while the limit
switch is open. The gas valve is de-energized. Power to
the thermostat “R” is removed while the limit switch is
open.
When the limit switch re-closes, the induced draft motor
runs through its post purge and the indoor blower goes
through the heat off delay.
If a call for heat exists when the limit switch re-closes, the
control goes through a pre-purge period and then makes
an ignition attempt. The indoor blower remains on (for the
delay off time) during the re-ignition attempt.
1. If no voltage is measured on either side of control it
indicates ignition control or wiring to control problem.
2. If voltage is measured on one side of the control and
not the other, it indicates the control is open.
3. If voltage is measured on both sides of the control the
wiring to gas valve or valve is at fault.
Servicing procedure with furnace not firing.
1. Confirm that the outer door was in place and all
screws tightened. (No leaks under the door.)
2. Check to see if any damage was done to the furnace
especially the wiring.
3. Confirm that heat exchanger is not obstructed by
feeling for discharge air from the flue hood when
the combustion blower is running but the unit is not
firing.
If the above steps do not suggest the reason the control
has tripped the furnace should be fired.
1. Remove the heating compartment door.
2. Turn of the power or open the thermostat circuit.
3. Reset the rollout control.
4. Turn power on and put the unit into a call for heating.
CAUTION
Flame rollout could occur. Keep face and hands a
safe distance from burner area.
Summary of Contents for DRG0361DL00001S
Page 20: ...20 SYSTEM OPERATION...
