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Other Unit Adjustments
Primary Limit
The primary limit is located on the heating compartment
vestibule panel. This limit is factory set and requires no
adjustment.
Flame Rollout Switches (Two)
These manually reset switches are located on the inside of
the burner box. If tripped, check for adequate combustion
air before resetting.
Pressure Switches (Two)
The pressure switches are located on the cold end header
box. These switches check for proper combustion air
inducer operation before allowing ignition trial. The switches
are factory set and require no adjustment. Pressure switch
tubing installation is critical for safe operation. See Figure
60 below.
High-Fire
Pressure
Switch
Cold End
Header Box
Low-Fire
Pressure
Switch
Gas Valve
1. Black tubing from front port on low-fire pressure switch to
positive port on the gas valve.
2. Red and black tubing from rear port on low-fire pressure
switch to the negative port on the gas valve.
3. Red and black tubing from front port on high-fire pressure
switch to negative port on cold end header box.
4. Black tubing from rear port on high-fire pressure switch to
positive port on cold end header box.
Figure 60. Pressure Switch Tubing Installation
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Temperature Rise
After the furnace has been started and supply and return
air temperatures have been allowed to stabilize, check the
temperature rise with the unit operating at 100 percent
firing rate. If necessary, adjust the blower speed to maintain
the temperature rise within the range shown on the unit
nameplate. See Table 22 for allowable heating speeds.
Increase the blower speed to decrease the temperature.
Decrease the blower speed to increase the temperature.
Failure to adjust the temperature rise may cause erratic
limit operation.
Thermostat Heat Anticipation
Set the heat anticipator setting (if adjustable) according to
the amp draw listed on the wiring diagram that is attached
to the unit.
Electronic Ignition
The integrated control has a feature that serves as an
automatic reset device for ignition control lockout caused
by ignition failure. This type of lockout is usually due to low
gas line pressure. After one hour of continuous thermostat
demand for heat, the control will break and remake
thermostat demand to the furnace and automatically reset
the control to begin the ignition sequence.
Exhaust and Air Intake Pipe
1.
Check exhaust and air intake connections for tightness
and to make sure there is not blockage.
2.
Are pressure switches closed? Obstructed exhaust
pipe will cause unit to shut off at pressure switches.
Check termination for blockages.
3.
Reset manual flame rollout switches on burner box
cover.
507029-05
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