Operating sequence, Heating mode, Ating sequence – Reznor R6GI Unit Installation Manual User Manual
Page 19: Operating sequence section
19
OPERATING SEQUENCE
The operating sequences for the heating, cooling, and
fan modes are described below. Refer to the field and
furnace wiring diagrams:
Heating Mode
1. On a call for 1st stage heat, the thermostat closes and
applies 24 VAC to terminal W1 on the control board.
2. Safety Circuit Proving - The control board verifies
continuity through the 24VAC limit control circuit. If the
high temperature limit switch and flame roll-out switch
are closed and both the high and low vent pressure
switches are open, the control board will then begin
pressure switch proving. If an open limit is detected, the
control board will energize the indoor blower motor and
operate it continuously while the limit switch circuit is
open. All other system functions will be inoperable until
the limit circuit closes. While the limit circuit is open, the
control will display Open Limit Switch Fault. See
3. The furnace control checks for continuity (24 VAC)
across the pressure switch. If either the high or low
pressure switch is closed, the heat mode sequence
will not continue. If either remains closed, the control
will display a Pressure Switch Closed with Inducer Off
Fault until the fault condition clears.
4. Pressure Switch Proving - The control energizes the
induced draft motor on High speed and waits for the
high and low pressure vent switch to close. If the low
pressure switch does not close within 12 seconds, the
control will display a Pressure Switch Open with Inducer
On Fault. If the pressure switches do not close before
60 seconds expires, the control will de-energize the
inducer for 5 minutes and continue to display a Pressure
Switch Open with Inducer On Fault during the 5 minute
inducer off period. After the inducer has been off for 5
minutes, the control energizes the inducer motor and
restarts the 60 second pressure switch proving period.
5. Pre-Purge - If the low pressure switch closes the control
runs the inducer on high speed for a 30 second pre-
purge time while monitoring the thermostat call for heat,
limit switch circuit, high and low pressure switch, and
flame sense.
6. Igniter Warm Up - When the 30 second pre-purge time
has elapsed, the control begins the Hot Surface Ignition
(HSI) warm-up as follows:
Initial Power up: After 30 seconds of igniter warm-up, the
gas valve will open. The igniter circuit will stay energized
for 3 seconds after the gas valve opens.
After Initial Power up: The control has a programmed
adaptive ignition feature which varies the warm-up
period as follows: If ignition is successful the warm-up
is reduced by 3 seconds on each subsequent call for
heat until ignition failure occurs. Upon ignition failure,
the warm-up is increased by 3 seconds on the next try.
If successful, the timing remains fixed at this level. In
general, whenever ignition failure occurs the warm-up
interval is increased by 3 seconds on the next try. And
if successful, it remains there. Minimum and maximum
warm-up time limits are set at 9 and 54 seconds.
7. Flame Proving / Ignition / Low Heat Operation - The
furnace control must prove flame via the flame sensor
5 seconds after the high main gas valve is energized.
• If flame is sensed, burners are on and the igniter
cools off. The yellow LED will be lit.
• If no flame is sensed, the gas valve closes
immediately and the inducer continues to run on
high. A second trial for ignition (step 6) begins. If
no flame is sensed on the fifth try for ignition, the
furnace control is locked and the control will display 1
Hour Lockout Fault. The thermostat must be opened
for at least 10 seconds to reset the furnace control
after a lock out. Otherwise, the furnace will attempt
another ignition sequence in 1 hour.
Low Fire Heat (Stage 1): If flame is present at the end
of the trial for ignition time, the control leaves High main
gas valve energized and inducer motor on High speed
for the first 15 seconds, and begins the heat blower
22 second on delay. Control inputs are continuously
monitored while the call for heat remains. The control
will always energize the gas valve on High fire with the
inducer on High speed for the first 15 seconds of any
heating cycle. After this 15 second period, the control
switches the gas valve to Low fire and inducer to Low
speed if no second stage (W2) demand is present.
8. Blower Start-Up - After flame is proven, the furnace
control energizes the circulating air blower after 22
seconds. The blower will then ramp up to the airflow
selected for heating.
9. High Heat Staging (with 2 Stage Heat Thermostat) - Unit
will always start in High heat operation. See step 7 for
start up sequence. After the initial 15 second start up
sequence is satisfied, the control will move to Low heat
and wait for a W2 call from a 2-stage thermostat. After a
second stage heat demand is present (W2 energized),
the gas valve will open to High heat mode increasing
the flow of gas to the burners while the inducer and
blower motor ramp to high speed.
Single Stage Heat Thermostat with Automatic Heat
Staging - Automatic heat staging allows the unit to
operate as a two stage gas furnace with the use of
a single stage heating thermostat. With the ignition
control AUTO HEAT STAGE jumper repositioned from
the OFF position to the ON position, the gas furnace
will automatically switch to High heat mode of operation
after a 10 minute delay. The induced draft motor and
blower motor will both ramp to high speed. See
10. When the thermostat has been satisfied, gas valve is
de-energized.