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SGH/SCH036, 060, 120, 240
Electric Heat Start-Up
Electric heat will stage on and cycle with thermostat
demand. Number of stages of electric heat will vary
depending on electric heat assembly. See electric heat
wiring diagram on unit for sequence of operation.
Heating Operation and Adjustments
(SG Units)
A-Heating Sequence of Operation
1- On a heating demand the combustion air inducer starts
immediately.
2- Combustion air pressure switch proves inducer
operation. After a 30-second pre-purge, power is
allowed to ignition control. Switch is factory set and
requires no adjustment.
3- Spark ignitor energizes and gas valve solenoid opens.
4- Spark ignites gas, ignition sensor proves the flame and
combustion continues.
5- If flame is not detected after 8 seconds, the ignition
control will repeat steps 3 and 4 two more times. The
ignition control will wait 5 minutes before the ignition
attempt recycles.
6- For troubleshooting purposes, an ignition attempt after
lock out may be re-established manually. Move
thermostat to “OFF” and return thermostat switch to
“HEAT” position.
Primary Limit Location
Limit controls are factory-set and are not adjustable.
SG 036 & 060 -
On the vestibule to the right of the
combustion air inducer. See figure 32.
SG 120
- Upper right corner of blower support wall.
SG 240
Secondary Limit Location
(none on 3, 5, 20-ton units)
SG 120
- Top back side of blower housing.
B-Heating Adjustment
Main burners are factory-set and do not require adjustment.
C-Two-Stage Gas Manifold Pressure Adjustment
IMPORTANT - Do not set low fire pressure lower than
the certified minimum input rating listed in table 22.
Gas manifold pressures should match pressures shown in
table 22. On two stage gas valves, initiate a W2 thermostat
demand to check high fire pressure before low fire pressure.
With high fire operating, reduce the thermostat demand to
W1 and check the low fire pressure.
HEAT SECTION - 036 & 060 UNITS
FIGURE 32
FORMED
BURNERS
COMBUSTION
AIR INDUCER
VENT
CONNECTOR
GAS VALVE
PRIMARY
LIMIT
SG/SC 240 PRIMARY LIMIT LOCATION
FIGURE 33
LIMITS
DRIP
SHIELD
TABLE 22
Manifold Input Pressures
-
in.wg. (kPa)
Unit
Natural Gas
Propane (LP) Gas
1st Stage
+ 0.2 (+.05)
2nd Stage
+ 0.3 (+.08)
1st Stage
+ 0.2 (+.05)
2nd Stage
+ 0.3 (+.08)
036, 060
2.0 (0.50)
3.5 (0.87)
5.9 (1.47)
10.5 (2.61)
120, 240
1.6 (0.40)
3.7 (0.92)
5.5 (1.37)
10.5 (2.61)
