Operation; Troubleshooting - White Rodgers 21V51U-843 Installation Instructions Manual

OPERATION

NORMAL OPERATION – HEAT ON
When the thermostat calls for heat the module verifies the
pressure switches are open and energizes the inducer (high
speed) and optional humidifier contacts. When the low pressure
switch contacts close a 15 second pre-purge begins. After 15
seconds the inducer switches to low speed and the 120 VAC
ignitor is energized. The ignitor warms up for 17 seconds and
the gas valve is energized on low fire. Flame must be detected
within 4 seconds. If flame is detected, a 45 second heat,
fan on time delay begins. This allows the heat exchanger to
warm up before energizing the circulator on low speed and
(optional) Electronic Air Cleaner contact. When the thermostat
(or module) initiates second stage the inducer is energized at
high speed.
This closes the second stage inducer pressure switch then
energizes the second stage on the gas valve and then the high
heat circulator speed.
NORMAL OPERATION – HEAT OFF
When the thermostat satisfies for second stage, the control
will switch high speed inducer and high fire gas valve to low
speed inducer and low fire gas valve. After the 30 second high
heat fan delay the circulator will drop to low speed. When the
thermostat satisfies for first stage the gas valve de-energizes
and the inducer will run low speed for a 15 second post-purge.
The circulator runs until the heat off delay ends.

TROUBLESHOOTING

SYSTEM LOCKOUT
When a system lockout occurs (1hour), the gas valve is de-
energized, the low speed inducer blower is energized for the
60 second interpurge period and the circulator is energized for
selected heat off delay if it was previously ON. The diagnostic
indicator light will flash the fault that is present (refer to
diagnostic table).
To reset the control after system lockout, do one of the
following:
System Reset
Remove 24 VAC power to the control for twenty (20) seconds
or longer to reset the control.
Thermostat Reset
Remove the call for heat from the thermostat for a period of
between (1) second and less 20 seconds. If flame is sensed
with the gas valve de-energized, interrupting the call for heat
at the thermostat will not reset the control.
Auto Restart
After one (1) hour of internal or external lockout, the control
will automatically reset itself and go into an auto restart purge
for 15 seconds.
DIAGNOSTIC FEATURES
The control continuously monitors its own operation and the
operation of the system. If a failure occurs the diagnostic
indicator LED (DSI) will flash a "RED" failure code. If a failure
is internal to the control the "RED" indicator will stay on
8
Note: If the module is configured for a single stage thermostat
and running on second stage when the call for heat ends, the
circulator will drop to low speed after 30 seconds and continue
until the heat off delay ends.
COOL MODE
In a typical system, a call for cool is initiated by closing Y
and G. This energizes the compressor and the electronic air
cleaner (optional). The electronic air cleaner and the G and (Y
or Ylo outputs to the Circulator motor will energize after the 5
second cool on delay period. After the thermostat is satisfied,
the compressor is de-energized and the control starts a 60
second cool circulator speed off delay. After 60 seconds the
circulator is de-energized.
MANUAL FAN ON MODE
If the thermostat fan switch is moved to the "ON" position, the
electronic air cleaner (optional) and the G circulator output to
the circulator motor will be energized. When the fan switch is
returned to the AUTO position, the G circulator output and the
electronic air cleaner are de-energized.
continuously. In this case, the entire control should be
replaced as the control is not field-repairable. If the LED
is continuously OFF, there may be no power to the control
or a failure within the control. If the sensed failure is in the
system (external to the control), the LED will flash RED in
the sequence listed in the Diagnostic Table. The LED will also
indicate "System Status" as per the Amber and Green LED
signatures listed in the Diagnostic Table. The LED will flash one
RED flash at power up.
CFM INDICATOR
The LED (DS2) CFM flashes when the blower motor is running.
The flashing indicates the motor CFM (cubic feet per minute)
air flow designated by the furnace manufacturer. Consult the
furnace manufacturer for flash code detail.
FAULT CODE RETRIEVAL
To retrieve fault codes, push and release the "LAST ERROR"
button for more than 1/5 second and less than 5 seconds.
(Control will indicate this period by solid GREEN for 1/5 secs.
to 5 secs.). The LED will flash up to five stored fault codes,
beginning with the most recent. If there are no fault codes in
memory, the LED will flash two green flashes. The control will
flash the most recent error first and the oldest error last (last in
first out). There shall be 2 seconds between codes. Solid LED
error codes will not be displayed.
NOTE
These error codes may be different from furnace label or
furnace manual.