Page 19
Unit Adjustments
HIGH LIMIT AND CAPILLARY TUBE LIMIT
The high limit and manuallyĆreset capillary tube limit are
both located on the heating compartment vestibule panel.
Both limits are factory set and do not require field adjustĆ
ment.
When there is inadequate supply air (a high supply air
temperature), the high limit shuts off the gas supply to
the burners, turns the combustion air blower
OFF
, and
keeps the air circulating blower
ON
until the limit resets
itself. While the limit is open, the control board displays
DIAG.1 - FLASHING; DIAG.2 Ć ON.
If the limit trips 5
times in succession, a 60 minute Watchguard" occurs.
After 60 minutes, the control board automatically resets
itself. (The control board can also be reset by switching
the thermostat from
HEAT
to
OFF
and then back to
HEAT
again.)
When there is inadequate supply air (a high supply air
temperature), the manuallyĆreset capillary tube limit
shuts off the gas supply to the burners and turns both the
combustion air blower and the air circulating blower
OFF.
(The air circulating blower turns off only after its preset
delayĆoff time expires). While the limit is open, the control
board then displays
DIAG.1 - ON; DIAG.2 Ć FLASHING
.
To reset the limit, allow the furnace to cool, and then push
the switch on the limit's face inward.
If either limit trips, check for clogged filters or blocked supĆ
ply/return air grilles.
COMBUSTION AIR PRESSURE SWITCH
The combustion air pressure switch is located on the
heating compartment vestibule panel. This switch checks
for proper combustion air fan operation before allowing
ignition trial. The switch is factoryĆset and requires no field
adjustment.
FAN CONTROL
The fan control is part of the control board located on the
heating compartment vestibule panel. The preset fan on
delay time of 45 seconds is not adjustable. The fan off
delay time is factory adjusted at
120 seconds and can be
adjusted by moving the jumper on the integrated control
board. See figure 24 for settings.
120
180
90
60
To adjust fan-off timings:
Remove jumper and select one of the
other pin combinations to achieve the
desired time.
TIMING
JUMPER
TIMING PINS
(seconds)
FAN-OFF TIME ADJUSTMENT
FIGURE 24
GAS FLOW
To check for proper gas flow to combustion chamber, deterĆ
mine heat (kW) input from the unit rating plate. Divide this
input rating (MJ/hr) by the calorific value per unit volume
(MJ/m
3
) of the gas being used. Result is the volume of gas
required per hour. Determine the flow of gas through gas
meter for two minutes and multiply by 30 to get the hourly
flow of gas.
GAS PRESSURE
1 - Check the gas line pressure with unit firing at maximum
rate. See technical data table on page 22 for minimum
and maximum allowable pressure.
2 - After line pressure has been checked and adĆ
justed, check manifold pressure. Manifold pressurĆ
es are given in technical data table on page 22. See
figure 23 for gas pressure adjustment screw location.
TEMPERATURE RISE
Check the temperature rise and, if necessary, adjust fan
speed to maintain the temperature rise within range
shown on the unit rating plate.
If outdoor air is added to the recirculating room air, the
mixed air temperature at the heat exchanger should not
be lower than 15.5
°
C for extended periods of time.
THERMOSTAT HEAT ANTICIPATION
Set thermostat heat anticipation to:
0.80 amps
S.I.T. gas valve
ELECTRICAL
1 - Check all wiring for loose connections.
2 - Check for correct voltage at the furnace (furnace opĆ
erating).
3 - Check amp-draw on fan motor.
Motor Nameplate__________Actual__________
FAN SPEEDS
Note - CFM readings are taken external to unit with a dry
evaporator coil and without accessories.
1 - Turn off electrical power to furnace.
2 - Remove unit access panel.
3 - Disconnect existing speed tap at control board
speed terminal.
NOTE - TERMINATION OF ANY UNUSED MOTOR
LEADS MUST BE INSULATED.
4 - Refer to fan speed selection chart on unit wiring diaĆ
gram for desired heating or cooling speed.
5 - Connect selected speed tap at control board speed
terminal.
6 - Resecure blower access panel.
7 - Turn on electrical power to furnace.
FLUE AND CHIMNEY
1 - Check flue pipe, chimney and all connections for
tightness and to make sure there is no blockage.
2 - Check unit for proper draught.
3 - Is pressure switch closed? Obstructed flue will cause
unit to shut off at pressure switch. Check flue and
outlet for blockages.
