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UH-PRC002-EN38
Electric
Power
High-Efficiency Units
NOTE: On duct furnaces, the fan motor
and associated controls shown in the
wiring diagrams are not integral to the
unit. It is essential, however, that the air
handling system be interlocked with the
duct furnace to prevent duct furnace
operation without airflow.
Single-Stage Control
With power applied to the unit:
1
The thermostat calls for heat.
2
The pressure switch measures the flow
through the vent system and energizes
the intermittent pilot when the flow is
correct. CAUTION: THE PRESSURE
SWITCH MUST NOT BE BYPASSED.
THE UNIT MUST NOT BE FIRED UNLESS
THE FLUE VENT FAN IS OPERATING. If
this procedure is not followed, there may
be a gas buildup that could cause an
explosion.
3
The pressure switch closes and activates
the flue vent fan.
4
The pilot valve opens.
5
The ignitor sparks continuously to ignite
the pilot.
6
The sensor proves pilot ignition and
shuts off the ignitor.
7
With the pilot lit, the main gas valve
opens.
8
Main burners are lit at 100 percent of the
unit’s rated input.
9
The fan time delay relay allows the
heater to come up to operating
temperature. At this time, the fan time
delay relay closes and activates the fan
motor.
10
The unit continues to fire until the
thermostat is satisfied and no longer
calls for heat.
11
The main and pilot valve close.
12
The pressure switch opens and
deactivates the flue vent fan.
13
The fan time delay relay remains closed,
keeping the fan operating to dissipate
residual heat from the heat exchanger. At
this time, the fan time delay relay opens
and deactivates the fan motor.
• Caution - Disconnect power before
servicing.
• Unit must be grounded.
• Use copper conductors only.
• If any of the original wire as supplied
with the appliance must be replaced, it
must be replaced with wiring material
having a temperature rating of at least
125°C.
• Hi-limit and blocked vent (spill) wires
minimum 200°C.
• Refer to installation instructions for
venting, gas piping and start-up
procedures.
• - - - Indicates Field Wiring.
• ___ Indicates Factory Wiring.
L2
L1
L1
L1
L1
8
LINE IN
115-240/1/60
TIME DELAY
SUMMER
WINTER
RELAY 1
L2
L2
BLOWER
MOTOR
T1
115-240/24V
50VA
DRAFTOR
MTR.
2
1
R
R
W
W
THERMOSTAT
HIGH LIMIT
1
3
2
DRAFTOR
PRESS. SW.
58600
IGNITOR
MV SOL.
MV
MV/PV
PV
GND
24V (HOT)
24V (GND)
SPARK
IGN
PV SOL.
RELAY 1
R
TIME DELAY
TD