7
SELF-TEST
The 21V51D-751 furnace control is equipped with a self-test
routine used during the control’s installation. Self-test checks
the functionality of the control, ignitor, inducer, and blower to
verify they are in proper working order. Ensure thermostat is
turned OFF or thermostat wires are disconnected to enable.
NOTE
The self-test functionality is available after power up and
until a solid green LED is present (5 seconds after power
up). During this time, the control will ignore all active
calls. If a solid green LED is present, disconnect power
for 10 seconds and refer above to enter self-test routine.
Enter Self-Test by:
• Turn on power and manually close blower door switch.
• Wait 1 second.
• Slowly double-click SELECT button within 3 seconds.
Sequence is as follows:
• LED will flash in red the previous error code 4 times
• Afterward, the LED will slowly flash alternate colors (red,
amber, green) to indicate Self-Test is active and continue
until Self-Test is complete
• Inducer motor will turn ON at HIGH speed and continue
running until Self-Test is complete
• After 7 seconds, the ignitor will turn ON for 15 seconds,
then OFF
• Blower motor operates on LOW HEAT speed for 10
seconds
• Blower motor operates on HIGH HEAT speed for 10
seconds
• Blower motor operates on COOL speed for 10 seconds
• Blower motor turns OFF
• Inducer motor goes to LOW speed for 10 seconds and
then turns OFF
• LED will display solid green to indicate Standby mode
OPERATION
HEAT PUMP MODE
When installed with a heat pump, the furnace control automatically changes the timing sequence to avoid long blower off times
during defrost cycles.
Output
Standb
y
Call f
or Heat Pump
Heat Pump ON Dela
y
Heating until
Thermostat
is Satisfied
Call f
or Defr
ost
Self Chec
k
Pre-Pur
g
e
Ignitor W
arm-Up
Ignition Activ
ation P
eriod
Heat ON Dela
y
Blo
wer Sta
ging
Defrost
until
Unit is
Satisfied
Heating
until Ther-
mostat is
Satisfied
P
ost-Pur
g
e
Blo
wer Off Dela
y
System Off
Thermostat - W/W1
Thermostat - Y/Y2
Thermostat - Y1
3 s
15 s 17-19 s <5 s 5 s 5 s
15 s 90, *120, 150, 180 s
Hi Speed Inducer (IND HI)
Low Speed Inducer (IND LO)
Pressure Switch (HPS)
Pressure Switch (LPS)
Ignitor (HSI)
Second Stage Gas (MVH)
First Stage Gas Valve (MVL)
Flame Sensor (FS)
Blower (Cool Speed)
Blower (High Heat Speed)
Blower (Low Heat Speed)
Humidifier (24V)
EAC
LED
Green LED
– 1 flash
Green
LED – 2
flashes
Amber LED – 3 flashes
Green – ON
