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THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
Flame rectification sensing is used on all units. Loss of
flame during a heating cycle is indicated by an absence of
flame signal (0 microamps). If this happens, the control will
immediately restart the ignition sequence and then lock
out if ignition is not gained after the third trial. See System
Service Checks section for flame current measurement.
The control shuts off gas flow immediately in the event of
a power failure. Upon restoration of gas and power, the
control will restart the ignition sequence and continue until
flame is established or system locks out.
On a heating demand, the ignition control is energized by
the A55 Unit Controller. The ignition control then allows
30 to 40 seconds for the combustion air blower to vent
exhaust gases from the burners. When the combustion
air blower is purging the exhaust gases, the combustion
air prove switch is closing proving that the combustion air
blower is operating before allowing the ignition control to
energize. When the combustion air prove switch is closed
and the delay is over, the ignition control activates gas
valve, the spark electrode and the flame sensing elec-
trode. Sparking stops immediately after flame is sensed.
The combustion air blower continues to operate through-
out the heating demand. If the flame fails or if the burners
do not ignite, the ignition control will attempt to ignite the
burners up to two more times. If ignition cannot be ob-
tained after the third attempt, the control will lock out. The
ignition control is not adjustable.
13-Balance Point Thermostat A526
When outdoor air temperature is above setpoint (35°F
+ 5F° default), the unit will operate in heat pump mode.
When outdoor air temperature falls below setpoint, the
unit willoperate in gas heat mode. The balance point set-
point can be adjusted using the following mobile service
app menu path:
Go to RTU MENU > SETTINGS > RTU OPTIONS > EDIT
PARAMETER = 526 (HP DF BALANCE POINT)
Note - Only stage one is used; stage 2 is not used.
Although the recommended balance point setpoint is 35F,
the setpoint can be adjusted. Weigh the comfort / cost
benefit when increasing the setpoint.
IGNITION CONTROL TIMING
ON
SECONDS 0
30
OFF
GAS VALVE
IGNITION SPARK
BLOWER
IGNITION TRIAL
6 (+3.4, -2.0) SEC.
30
30
1
2
FIGURE 16
II-PLACEMENT AND INSTALLATION
Make sure the unit is installed in accordance with the in-
stallation instructions and all applicable codes. See ac-
cessories section for conditions requiring use of the op-
tional roof mounting frame (LARMF).
III-START UP - OPERATION
Refer to start-up directions and refer closely to the unit
wiring diagram when servicing. See unit nameplate for
minimum circuit ampacity and maximum fuse size.
A-Preliminary and Seasonal Checks
1 - Make sure the unit is installed in accordance with
the installation instructions and applicable codes.
2 - Inspect all electrical wiring, both field and factory
installed for loose connections. Tighten as required.
Refer to unit diagram located on inside of unit
control box cover.
3 - Check to ensure that refrigerant lines are in good
condition and do not rub against the cabinet or
other refrigerant lines.
4 - Check voltage at the disconnect switch. Voltage
must be within the range listed on the nameplate.
If not, consult the power company and have the
voltage corrected before starting the unit.
5 - Recheck voltage and amp draw with unit running. If
voltage is not within range listed on unit nameplate,
stop unit and consult power company. Refer to unit
nameplate for maximum rated load amps.
6 - Inspect and adjust blower belt (see section on
Blower Compartment - Blower Belt Adjustment).
B-Heat Pump Start Up
Note - The outdoor air ambient temperature must be above
the heat pump balance point setpoint (35_F default) to en-
able heat pump operation. The balance point setpoint can
be adjusted using the following mobile service app menu
path: Go to RTU MENU > SETTINGS > RTU OPTIONS
> EDIT PARAMETER = 526 (HP DF BALANCE POINT)
Page 27
END OF
THERMOSTAT
DEMAND
HEATING
CYCLE
3
42 SEC.
122 SEC.
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