Rheem RGRK-12ERAJS Series Installation Instructions Manual page 52

gas valve to 100% and the main
blower goes to high-fire heating
speed.
f. When the thermostat cycle ends, the
gas valve de-energizes, and the
burners go out.
g. The draft inducer will continue
running for a 10 second post purge.
h. The main blower will run for for the
user-defined blower-off delay (this
timing is field adjustable, for 90, 120
150, or 180 seconds at Jumper P6 on
the furnace control board). See Figure
48 for switch settings.
Sequence if the system doesn't light
or doesn't sense flame:
a. If flame is not sensed within 8
seconds after the gas valve energizes,
the valve and the ignitor are de-
energized. The induced draft motor
will, stop momentarily, and then restart
to check PS operation.
b. The ignition process goes through
three more tries.
c. If there is no ignition after the fourth
trial, the furnace goes into soft lockout
for one hour.
d. The sequence repeats after a one
hour delay and continues repeating
until ignition is successful or the call
for heat is terminated.
e. To reset the lockout, break power
either at the thermostat or at the unit
disconnect switch for 30 seconds. The
furnace will then go through another
set of trials for ignition.
f. If flame is established and maintained
during the trial for ignition period and
flame is lost, the gas valve is de-
energized, the draft inducer stops after
a 10-second post-purge. The blower
motor runs at the high-fire or low-fire
heating speed (depending on state
when flame was lost) until it completes
the blower-off delay.
When the blower-off delay is over, the
control initiates another ignition trial
period by starting the inducer for the
pre-purge. The control will recycle up
to 5 flame losses (4 re-cycles) within a
single call for heat before going into
lockout.
TO SHUT DOWN FURNACE
1. Set the room thermostat to its lowest
setting.
2. Shut off the gas to main burners by
setting the gas control switch to the
"OFF" position, or by turning the
manual gas stop closed.
Sequence of operation with two
stage thermostat
See the section of this book titled
"Electrical Wiring - Thermostat" for a
wiring diagram showing how to connect
a thermostat.
Connect W1 on thermostat to W on IFC.
Connect W2 on thermostat to W2 on
IFC.
Call for 1st stage heat
a. R and W thermostat contacts close
and the IFC runs a self check routine.
After the IFC verifies that both sets of
pressure switch contacts are open,
the induced draft motor starts on high
until both pressure switch contacts
close (a maximum of 60 seconds).
52
b. After a 30 second pre-purge the spark
igniter energizes and the gas valve
(high stage) opens, lighting the
burners.
c. After the burners light, the remote
flame sensor must prove ignition. If the
burners do not light or flame cannot be
proven, the system goes through
another ignition sequence. It does this
up to 4 times.
d. Twenty seconds after flame sense,
the main blower energizes on low
speed, the gas valve drops to low fire,
and the inducer drops to low speed.
The furnace continues to run on low
until the call for heat is satisfied or the
second-stage contacts close. If the
first-stage call for heat is satisfied the
gas valve de-energizes and the
induced draft motor continues running
for a 10 second post purge time. The
main blower runs for the user-defined
blower-off delay (this timing is field
adjustable at Jumper P6). See Figure
48 for switch settings.
Call for 2nd stage heat after 1st stage
R and W2 thermostat contacts close,
calling for 2-stage heat. The induced
draft motor then switches to high
speed and the high pressure switch
contacts will close. The gas valve
switches to high fire and the main
blower switches to high-fire heating
speed.
2nd stage heat satisfied, 1st stage
heat still required.
R and W2 thermostat contacts open (W1
to R remains closed). The induced draft
motor switches to low speed, the main
blower motor switches to low-fire heating
speed and the gas valve changes to low.
The furnace continues to run in this mode
until the first-stage heat call is satisfied.
The system will shut down as noted in
"d," under first-stage call for heat.
Call for second-stage heat with no
other existing heat call present.
a-c. Same operation as call for first-stage
heat
FIGURE 48
TWO-STAGE, 90 PLUS IFC JUMPER SELECTIONS
d. Main blower starts on high speed
20 seconds after gas valve
energizes. The furnace continues
to run on high until the W2
contacts open. If W2 and W1
open at the same time (both high
& low stages are satisfied), the
gas valve de-energizes and the
inducer continues to run for a 10-
second post-purge. The main
blower runs for the user selected
blower-off delay. See Figure 48
for switch settings.
NOTE: Under certain conditions the
furnace may alternate between low
and high fire continuously. This
operation is based on demand from
the thermostat and is controlled by
the thermostat. This operation is
normal and can be expected at times
to maintain optimum comfort.
SETTING BLOWER TIMING
The UT ELECTRONIC CONTROLS
IFC has four quick connect terminals
for connecting the motor speed
leads. These are:
1. FAN SPEED/LOW — motor runs
on this speed when the
thermostat is in the "FAN ON"
position or when in low-fire
heating speed heat.
2. COOL — connect desired
cooling speed.
3. HEAT — connect desired high-
fire heating speed.
4. HEAT/COOL — connect desired
speed when high heating and
cooling speed are the same.
High fire and low fire blower timing
are the same.
IMPORTANT: Do not connect any
motor speeds to "HEAT" or "COOL" if
you use the "HEAT/COOL" terminal.