Catalogue
UH-PRC002-EN 43
Sequence of Operations
Separated Combustion Units
Single-Stage Control
With power applied to the unit:
1. The thermostat calls for heat.
2. The pressure switch measures the pressure differential between the air inlet and exhaust vent
systems. If the differential is correct, the intermittent pilot ignition is energized.
Important: CAUTION: THE PRESSURE SWITCH MUST NOT BE BYPASSED. THE UNIT MUST
NOT BE FIRED UNLESS THE FLUE VENT FAN IS OPERATING.
3. When the pressure switch is closed, the power venter motor is energized.
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.
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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 gas control.
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.
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See “Fan Control,” p. 30.
• 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.
• High-limit wires minimum 200°C.
• Refer to installation instructions for
venting, gas piping and start-up
procedures.
• - - - Indicates Field Wiring.
• ___ Indicates Factory Wiring.
L2
L1
DISCONNECT
LINE IN 115/1/60
L1
FAN TIME DELAY
L2
8
BLOWER/FAN
MOTOR
MTR
DRAFTOR
MOTOR
MTR
K5
BLACK
BLACK
LINE TO
24V XFORMER
50 VA
L2
8
12
24
VOLTS
2
SUMMER/WINTER SWITCH
W
S
L1
FAN TIME DELAY
DL
DRAFTOR ONE
K5
MV SOL.
PV SOL.
58600 IGNITOR
MV
MV/PV
PV
GND
24V (GND)
24V (HOT)
SPARK
PRESS. SW.
IGN
1
2
V
W1
R1
DL
HIGH LIMIT 1
1
3
2
1
W1
DL
V
2
T/D STAT
R
W/B
1