Service reference manual sequence of operations – Armstrong World Industries HWC PREMIER 183 User Manual
Page 39
Service Reference Manual
SEQUENCE OF OPERATIONS
2-29
SRM-HW/HWC 2/99
9.
With
W
de-energized, the
gas valve
closes immedi-
ately and the
induced draft blower
stops several
seconds later.
10. The
blower control board
starts a 90-second
circulating air blower
“off” delay. Approximately
90 seconds later, the blower stops.
FLAME SENSE
1.
During a call for heat, the
spark
terminal is ener-
gized and the
gas valve
is opened to light the
burners.
2.
The
ignition control
energizes the
spark
terminal
and the
gas valve
for approximately six seconds. If
a flame is not sensed in this time period, the
igni-
tion control
de-energizes the
spark
terminal and
the
gas valve
. This causes the
gas valve
to close
and the burners to shut off.
3.
Since the 24-volt signal has been sent to the
blower control board
, the
circulating air blower
times “on” in approximately 60 seconds.
4.
The
induced draft blower
continues to run for
approximately 30 seconds, then another trial for
ignition begins.
5.
The
ignition control
runs three trials for ignition. If
a flame is not sensed during these three trials, the
ignition control
will lockout.
6.
The
circulating air blower
continues to run until
the
R-W
circuit at the
thermostat
is interrupted.
7.
The
ignition control
remains in lockout until 24-volt
power to the
ignition control
is reset.
LIMIT OPENS
If the
limit switch
opens for any reason during a call for
heat, the following happens:
1.
If the
limit switch
senses that the temperature in
the unit is too high, the contacts between terminals
C
and
NC
on the
limit switch
open and the con-
tacts between
C
and
NO
close. This interrupts the
24-volt signal to the
pressure switch
and also de-
energizes terminal
P.SW
on the
ignition control
.
The
gas valve
closes immediately, as the 24-volt
signal to terminal
P.SW
is no longer present. The
induced draft blower
and the
circulating air
blower
continue to run. Power to
blower control
board
terminal
W
is maintained. The blower
continues to run until the
limit switch
closes or the
heat call at the
thermostat
is satisfied.
2.
When the
limit switch
senses that the tempera-
tures in the unit are normal, the contacts between
terminals
C
and
NO
open, the contacts between
terminals
C
and
NC
close and the operation of the
unit returns to normal.
PRESSURE SWITCH OPENS (BLOCKED FLUE)
1.
If blockage of the flue occurs, negative pressure in
the
induced draft blower
is reduced. At the set
point of the
pressure switch
, the contacts open.
This interrupts the 24-volt signal to terminal
P.SW
on the
ignition control
. The
gas valve
closes
immediately, as a relay in the
ignition control
opens and interrupts the signal to terminal
V2
of the
ignition control
.
2.
Terminal
W
on the
blower control board
stays
energized and the
circulating air blower
contin-
ues to run. If negative pressure is restored, the
pressure switch
closes and sends a 24-volt signal
to the
P.SW
terminal on the
ignition control
. The
ignition control
makes a trial for ignition again and
the operation returns to normal.
ROLLOUT SWITCH ACTIVATED
1.
If conditions in the burner compartment cause the
rollout switch
to trip, the contacts on the switch
open, interrupting the 24-volt signal going to termi-
nal
P.SW
on the
ignition control
. This causes the
ignition control
to de-energize terminal
V1
,
interrupting the 24-volt signal to the
gas valve
and
immediately closing it.
2.
The reason the
rollout switch
was tripped must be
determined before any corrective action is taken.
3.
The signal to terminal
P.SW
can only be restored if
the
rollout switch
is reset, which can only be done
manually. The
W
terminal on the
blower control
board
remains energized and the
circulating air
blower
continues to operate. Once the
rollout
switch
is reset, the operation of the unit returns to
normal.
CALL FOR COOLING
Line Voltage
On a call for cooling, the
thermostat
closes the circuit
between
Y
,
G
and
R
.
1.
With
Y
energized, the
contactor
closes. This
sends line voltage to
compressor
terminal
C
,
causing the
compressor
to start. The
outdoor fan
also starts, drawing air through the
outdoor coil
.
2.
Terminal
G
on the
blower control board
also
energizes at same time as
Y
. This starts the timer
on the
blower control board
. Approximately 15
seconds later (or immediately - see note on page 2-
30), the terminal marked
COOL
energizes. This
sends line voltage to the
circulating air blower
,
starting the blower.