5120416-XIM-C-0216
Johnson Controls Unitary Products
41
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Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature.
Electric Heat Anticipator Setpoints
It is important that the anticipator setpoint be correct. Too high
of a setting will result in longer heat cycles and a greater
temperature swing in the conditioned space. Reducing the
value below the correct setpoint will give shorter “ON” cycles
and may result in the lowering of the temperature within the
conditioned space. Refer to Table 18 for the required electric
heat anticipator setting.
Gas Heating Sequence Of Operations
The following sequence describes the operation of the gas heat
section.
When the thermostat calls for the first stage of heating, the low-
voltage control circuit from “R” to “W1” and “G” is completed,
thru the UCB. The heat relay “RW1” is energized. The “RW1-2”
contacts close energizing the draft motor control. The draft
motor control contacts close and start the draft motor. As the
speed of the draft motor reaches approximately 2500 RPM, the
centrifugal switch contact, located on the end of the draft motor
shaft, closes to power the first stage ignition module “IC1”, thru
the “RW1-1” contacts.
Ignition module “IC1” will immediately start the first stage igniter
sparking and will open the redundant valve located inside the
first stage main gas valve “GV1” to allow a flow of gas to only
the first stage carryover tube. Only after the pilot flame has
been ignited and the presence of pilot flame detected at the
“IC1” by a signal sent back through the flame sensor is sparking
terminated and the first stage main gas valve opened.
Gas flows into each of the main burners and is ignited from the
carryover tube flame.
After completing the specified fan on delay for heating, the UCB
will energize the blower motor.
If “IC1” fails to detect a pilot flame, it will continue to try for a
maximum of 85 seconds to ignite the pilot tube. If the pilot flame
is not detected, then “IC1” will lock out first stage furnace
operation for five minutes or until 24V power is removed from
the module either at the unit or by resetting the room
thermostat.
When the thermostat calls for the second stage of heating, the
low-voltage control circuit from “R” to “W2” is completed, thru
the UCB. Heat relay “RW2” is energized. The “RW2-1” contact
is closed energizing the second stage ignition module “IC2”.
“IC2” will immediately start the second stage igniter sparking
and will open the redundant valve located inside the second
stage main gas valve “GV2” to allow a flow of gas to the second
stage carryover tube. Only after the pilot flame has been ignited
and the presence of pilot flame detected at “IC2” by a signal
sent back through the flame sensor is sparking terminated and
the main gas valve opened.
Gas flows into each of the second stage main burners and is
ignited from the carryover tube flame.
If “IC2” fails to detect a pilot flame, it will continue to try for a
maximum of 85 seconds to ignite the pilot tube. If the pilot flame
is not detected, then “IC2” will lock out first stage furnace
operation for five minutes or until 24V power is removed from
the module either at the unit or by resetting the room
thermostat.
NOTE:
That the second stage furnace can operate even if first
stage has locked out.
When the thermostat satisfies de-energizing the “RW2”and
“RW1”, thus opening all gas valves. The blower motor will
continue to run after the furnace is shut down until the specified
fan off delay for heating has been satisfied. The UCB will de-
energize the blower motor.
Figure 23: Gas Valve Piping
When the thermostat calls for the first stage of heating, the low-
voltage control circuit from “R” to “W1” is completed. A call for
heat passes through the UCB to the ignition control board
(ICB). The UCB monitors the “W1” call and acts upon any call
for heat. Once voltage has been sensed at “W1”, the UCB will
initiate the fan on delay for heating, energizing the indoor
blower after the specified delay has elapsed.
When the thermostat has been satisfied, heating calls are
ceased. The GV is immediately de-energized. The blower is de-
energized after the fan off delay for heating has elapsed. The
draft motor performs a 25-second post purge.
Gas Heating Operation Errors
Temperature Limit
If the UCB senses zero volts from the high temperature limit,
the indoor blower motor is immediately energized. When the
UCB again senses 24 volts from the temperature limit, the draft
motor will perform a 25-second post-purge and the indoor
blower will be de-energized following the elapse of the fan off
delay for heating.
Table 18: Electric Heat Anticipator Setpoint
Heater
Kw
Voltage
Setting, Amps
Th1
Th2
18
380/415-3-50
0.29
-
36
0.29
0.29
54
0.29
0.29
72
0.29
0.29
Gas Valve
Gas main
Main valve
To main burner
Redundant valve
To pilot burner
