Service Reference Manual
SEQUENCE OF OPERATIONS
2-25
SRM-HW/HWC 2/99
9.
When
W
de-energizes, the
gas valve
immediately
shuts down and the
induced draft blower
also
stops after several seconds.
10. The
blower control board
starts a countdown to
blower “off”. Approximately 90 seconds later, the
circulating air blower
shuts down.
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 circuit between terminals
C
and
NC
on the
limit switch
opens. This closes the
circuit between terminals
C
and
NO
on the
limit
switch
, interrupting the 24-volt signal to the
pres-
sure switch
and the
rollout switch
and causing
terminal
P.SW
on the
ignition control
to de-
energize. The
gas valve
immediately closes, as
there is no longer a 24-volt signal at terminal
V1
on
the
ignition control
. With 24 volts still going to the
blower control board
and terminal
TH
on the
ignition control
, the
circulating air blower
and
induced draft blower
continue to run.
2.
The
circulating air blower
and the
induced draft
blower
continue to run as long as there is a call for
heat from the
thermostat
or the
limit switch
remains open.
3.
When the
limit switch
senses that the temperature
in the unit is low enough, the circuit between
C
and
NO
opens and the circuit between
C
and
NC
closes.
4.
With the
limit switch
closed, the unit again makes
a trial for ignition and returns to normal operation.
PRESSURE SWITCH OPENS (BLOCKED FLUE)
1.
If blockage of the flue occurs, the 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 coming from
terminal
NC
on the
limit switch
. Terminal
P.SW
on
the
ignition control
de-energizes, as does terminal
V1
. With loss of the 24-volt signal to the
gas valve
,
the valve closes immediately.
2.
Terminals
TH
on the
ignition control
and
W
on the
blower control board
remain energized. The
induced draft blower
and the
circulating air
blower
continue to run.
3.
When the
pressure switch
senses that there is
enough negative pressure within the flue, it will
again close the circuit between the l
imit switch
and
terminal
P.SW
on the
ignition control
.
4.
The unit makes a trial for ignition and returns to
normal operation.
Note: If the
P.SW
and
TH
terminals energize at the
same time, the
ignition control
will not respond.
A
pressure switch
being stuck closed is an
example of what would cause this to happen.
ROLLOUT SWITCH ACTIVATED
1.
If the conditions in the burner compartment cause
the
rollout switch
to trip, the contacts on the switch
open. This interrupts the 24-volt signal going to
terminal
P.SW
on the
ignition control
, causing
terminal
V1
on the
ignition control
to de-energize.
This interrupts the 24-volt signal to the
gas valve
and immediately closes it. Since terminal
TH
on the
ignition control
and
W
on the
blower control
board
remain energized, the
induced draft
blower
and the
circulating air blower
continue to
run.
2.
The 24-volt signal to the
ignition control
can only
be restored if the
rollout switch
is manually reset.
3.
Once the cause of the
rollout switch
being tripped
has been determined, the switch can be reset.
4.
With the
rollout switch
reset, terminal
P.SW
on the
ignition control
again energizes. The
ignition
control
makes a trial for ignition and operation
returns to normal.
Summary of Contents for HWC PREMIER 122
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