American Standard UHMB080ACV3VB Series Installer's Manual page 50

Installer's Guide
the YES and then press the ENTER button.
• Are you Sure and NO [NO] will now be displayed. With a NO/
NO question being asked, use the or arrows to select
the YES and then press the ENTER button.
• Turn 115VAC power off. When the Green LED on the
variable speed inducer drive goes out, turn 115 VAC
power back on.
• When the furnace is operating in the contingency mode
(stand alone operating cycle), the user interface will
display the following information. The top line will say
CNTNGNCY MODE. The bottom line will show the duty
cycle stage number STG (1 or 2) selected, and the percent
number 10-50 % selected.
• All furnace operating controls, pressure switches and
communications between the IFC and the variable speed
inducer drive and the variable speed indoor blower will
be functional during contingency mode operation of the
furnace.
• The  and ENTER buttons do not function in the
contingency mode of operation.
• To exit the contingency mode of operation turn off the
115 VAC power to the furnace.
• The contingency mode will stop for any of the following
reasons:
(1) If the furnace IFC receives a signal from the
communicating comfort control. This will only happen
if the data wire "D" from the comfort control has been
reconnected to the furnace IFC terminal board terminal
"D".
(2) Power is removed from the furnace and then turned
back on.
(3) The furnace IFC enters a RESET mode of operation.
(4) A fault is detected by the furnace IFC. Fault LED will
be flashing an Alert Code.
24V CONTINGENCY MODE
An alternative method for the contingency mode can be
used by changing the mode of operation in the Use
Interface to 24V mode and installing a conventional
24V comfort control.
To set this mode of operation:
Remove all wiring from the *CONT900 comfort control
and install a 24V comfort control. If the comfort
control requires a 24V common; connect R and
B to respective terminals. Connect a third wire to
"W". At the IFC, connect the same three wires to
the corresponding terminals. Jumper W1 to W2 at
the IFC. The stage delay between W1 and W2 can
be set by scrolling through the User Interface. It is
factory set to zero minutes but can be adjusted to 5,
10, or 15 minutes.
50
IFC INDUCER LEARNING ROUTINE SEQUENCE
• The furnace IFC will go through an inducer learning routine
for three pressure switches.
• The learning routine is done to determine the correct
amount of ventilation air for complete combustion.
• The inducer motor speed may be different for each
installation due to the different length and size of the
ventilation pipe, exhaust vent pipe, number of pipe
fittings used, and the type of vent cap installed.
• The inducer learning routine is repeated each time the
power to the furnace is interrupted. Once power is
restored and the furnace receives a call for heat, the
PS-1, PS-2 inducer learning routine will be initiated. The
furnace IFC will not go through a PS-3 inducer learning
routine until it receives a call for 100% (high) heat.
• To ensure the furnace heating efficiency is maintained
the furnace IFC will repeat the inducer motor learning
routine after :
150 Cycles at 40% (low) heat
100 Cycles at 65% (medium) heat
50 Cycles at 100% (high) heat
PS-1, PS-2 Inducer Learning Routine
• The furnace IFC checks pressure switches PS-1, PS-2,
and PS-3. They all have to be open before a heating
cycle can begin.
• The furnace IFC sends a digital signal to the variable
speed inducer drive to run the inducer motor at the
preset factory 65% (medium) heat RPM.
• The furnace IFC waits for the PS-1 and PS-2 pressure
switches to close. A 24 Volt AC signal is sent to the
furnace IFC when a pressure switch closes.
• If PS-1 and PS-2 do not close at the preset factory 65%
(medium) heat RPM, the furnace IFC will continue to
signal the variable speed inducer drive to increase the
inducer speed in steps until PS-1 and PS-2 close or until
the maximum RPM for 65% (medium) heat is reached.
• When PS-1 and PS-2 switches close, the furnace IFC will
then start the ignition cycle.
• The IFC now starts the igniter warm up cycle.
• Approximately 20 seconds later, the furnace IFC will turn
on the gas valve.
18-CD30D1-20-EN