Gas Pressure Adjustment - Lennox G51MP SERIES Installation Instructions Manual

White Rodgers 36G Series Gas Valve
INLET
PRESSURE
POST
GAS VALVE SHOWN IN OFF POSITION
FIGURE 55
Honeywell VR8205 Gas Valve with ON/OFF Switch
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
(under
barbed
fitting)
INLET
PRESSURE
PORT
GAS VALVE SHOWN IN ON POSITION
FIGURE 56
8 − White Rodgers 36G Gas Valve − Move gas valve
switch to ON. See figure 55 for the White Rodgers
36G valve
Honeywell VR8205 Gas Valve − Move gas valve
switch to ON. See figure 56 for Honeywell VR8205
valve.
9 − Replace the upper access panel.
10− Turn on all electrical power to to the unit.
11− Set the thermostat to desired setting.
NOTE − When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line.
12− If the appliance will not operate, follow the instructions
Turning Off Gas to Unit" and call the gas supplier.
Turning Off Gas to Unit
1 − Set the thermostat to the lowest setting.
2 − Turn off all electrical power to the unit if service is to be
performed.
3 − Remove the upper access panel.
4 − White Rodgers 36G Gas Valve − Move gas valve
switch to OFF.
OUTLET Honeywell VR8205 Gas Valve − Move gas valve
PRESSURE
switch to OFF.
POST
5 − Replace the upper access panel.
Heating Sequence Of Operation
When thermostat calls for heat, combustion air inducer
MANIFOLD
starts.
PRESSURE
ADJUSTMENT
Combustion air pressure switch proves blower opera-
SCREW
tion. Switch is factory set and requires no adjustment.
After a 15−second prepurge, the hot surface ignitor en-
ergizes.
After a 20−second ignitor warm−up period, the gas
valve solenoid opens.
MANIFOLD
PRESSURE
Gas is ignited, flame sensor proves the flame, and the
OUTLET
combustion process continues.
If flame is not detected after first ignition trial, the igni-
tion control will repeat steps 3 and 4 four more times
before locking out the gas valve ( WATCHGUARD"
flame failure mode). The ignition control will then auto-
matically repeat steps 1 through 6 after 60 minutes.
To interrupt the 60−minute WATCHGUARD" period,
move thermostat from Heat" to OFF" then back to
Heat". Heating sequence then restarts at step 1.

Gas Pressure Adjustment

Gas Flow (Approximate)
1 − Operate unit at least 15 minutes before checking gas
flow. Determine the time in seconds for one revolu-
tions of gas through the meter. A portable LP gas me-
ter (17Y44) is available for LP applications.
2 − Compare the number of seconds and the gas meter
size in table 10 to determine the gas flow rate. Multiply
the gas flow rate by the heating value to determine the
unit input rate. If manifold pressure is correct and the
unit input rate is incorrect, check gas orifices for proper
size and restriction.
3 − Remove temporary gas meter if installed.
NOTE − To obtain accurate reading, shut off all other gas
appliances connected to meter.
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