292453-UUM-A-0108
6
Unitary Products Group
NORMAL OPERATION SEQUENCE
The furnace control calculates the optimum firing rate each time the wall
thermostat R and W contacts close or open (at the beginning and at the
end of each call for heat) based on information from the thermostat and
past demand. UNLIKE CONVENTIONAL SYSTEMS, THE WALL
THERMOSTAT DOES NOT SIMPLY TURN THE FURNACE ON AND
OFF. THE FURNACE CONTROL CALCULATES THE DEMAND AND
MAY CONTINUE TO FIRE THE FURNACE DURING PORTIONS OF
THE THERMOSTAT "OFF" CYCLE.
When the wall thermostat R and W contacts close, indicating a call for
heat, the following sequence occurs:
1.
The inducer is energized and ramps up its speed until airflow is
proven by the pressure switch and by the pressure sensor on the
control board.
2.
The hot surface ignitor is energized.
3.
After a 17-20 second igniter heatup, the gas valve opens and the
burners light.
4.
When the control senses that flame is present, the circulating
blower starts at low speed.
5.
The furnace fires at 70% of full rate for 30-45 seconds, then drops
to the minimum (35%) firing rate.
6.
The firing rate is automatically adjusted to meet demand, increas-
ing gradually to maximum (100%) firing rate if the thermostat is not
satisfied within a defined time.
7.
When the thermostat R and W contacts open (thermostat is satis-
fied) the furnace control recalculates the demand and a new firing
rate.
a.
If demand exceeds the minimum firing rate, the burners will
continue to fire at a recalculated reduced firing rate, decreas-
ing if the thermostat remains off for a defined time.
b.
If demand does not exceed the minimum firing rate, the burn-
ers will shut off immediately.
8.
After the burners shut off, the circulating blower will continue to run
until the temperature sensor detects that the supply air tempera-
ture has dropped to the desired level, which should take from 30 to
90 seconds.
ADJUSTMENT OF FAN CONTROL SETTINGS
Cooling -
The airflow delivered by the furnace during cooling operation
can be adjusted to match the cooling capacity of the A/C condensing
unit. This is done by moving the COOL jumper on the control board to
give the desired airflow.
Do not move the motor wires to different positions on the
furnace control board!
The jumper has four positions, which will deliver sufficient airflow in
cooling mode for the cooling capacities shown in the table below. The
CFM delivery on each jumper position is shown in Table 14.
Continuous Fan Operation -
The airflow delivered by the furnace dur-
ing continuous fan operation can be adjusted as desired. This is done
my moving the FAN jumper on the control board to give the desired air-
flow.
Do not move the motor wires to different positions on the
furnace control board!
The jumper has three positions. The "A" position delivers maximum air-
flow, 100% of the blower capacity. Position "B" delivers approximately
70% of the blower capacity. And Position "C" delivers minimum airflow,
approximately 40% of the blower capacity.
Hot Surface Ignition System
TROUBLESHOOTING
The following visual checks should be made before troubleshooting:
1.
Check to see that the power to the furnace and the ignition control
module is ON.
2.
The manual shut-off valves in the gas line to the furnace must be
open.
3.
Make sure all wiring connections are secure.
4.
Review the sequence of operation. Start the system by setting the
thermostat above the room temperature. Observe the system’s
response. Then use the troubleshooting section in this manual to
check the system’s operation.
TABLE 2:
Cooling Airflow - A/C Capacity in Tons
Models
Jumper Position
D
C
B
A
60/1200
1-1/2
2
2-1/2
3
80/1200
1-1/2
2
2-1/2
3
80/1600
2-1/2
3
3-1/2
4
100/1600
2-1/2
3
3-1/2
4
100/2000
3
3-1/2
4
5
120/2000
3
3-1/2
4
5
FIGURE 6:
Furnace Control Board
HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a
match or any other means). There may be a potential
shock hazard from the components of the hot surface
ignition system. The furnace can only be lit automatically
by its hot surface ignition system.
Never bypass any safety control to allow furnace opera-
tion. To do so will allow furnace to operate under poten-
tially hazardous conditions.
Do not try to repair controls. Replace defective controls
with UPG Source 1 Parts.
Never adjust pressure switch to allow furnace operation.
ERROR
TEST
A
B
C
BLOWER
D’AUX
LOW VOLTAGE
TERMINALS
DIAGNOSTIC
LIGHT
TEST
BUTTON
LAST ERROR
BUTTON
CONTINUOUS
FAN SPEED
JUMPER
COOLING
SPEED JUMPER
HUMIDIFIER
TERMINALS
EAC
TERMINALS
