Reznor PDF2SF Unit Installation Manual - Manual (Page 21)

21
OPERATING SEQUENCE
The operating sequences for the heating, cooling, and
fan modes are described below. Refer to the field and
furnace wiring diagrams (Figures 14 - 17, pages 31 - 34).
2-Stage Heating Mode (Heat Pump)
1. On an initial call for heat, the thermostat closes and
applies 24 VAC to terminals G & Y1. NOTE: This closes
the compressor contactor and the compressor operates
on first stage. The reversing valve is not energized in
heating mode.
2. The control energizes the circulating blower at first stage
for the selected air flow.
3. If the thermostat is not satisfied in the required time
(based on the operation of the two-stage cooling
thermostat), Y2 will energize and the compressor will
run in 2nd stage. Refer to the thermostat installation
instructions for the heating profile.
4. When the thermostat is satisfied, terminals G & Y on the
control board are de-energized, opening the compressor
contactor.
5. If the thermostat does not satisfy on 2nd stage heat pump
mode, the thermostat or outdoor sensor will call for the
back-up gas heat. NOTE: If the unit is switching from
heat pump to furnace, the outdoor fan and compressor
will continue to run until flame ignition is detected in the
furnace. The indoor blower will continue to run.
gas Heating Mode - Emergency Heat &
Defrost Mode
1. On a call for 1st stage heat, the thermostat closes and
applies 24 VAC to terminal W 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 flash 1 on the red LED.
3. The furnace control checks for continuity (24 VAC)
across the pressure switch. If the pressure switch is
closed, the heat mode sequence will not continue. If it
remains closed for 10 seconds, the red LED will flash
3 times repetitively until the fault condition clears.
4. Pressure Switch Proving - The control energizes the
induced draft motor on High speed and waits for the
low pressure vent switch to close. If the low pressure
switch does not close within 60 seconds, the control
will flash 2 on the red LED. If the low pressure switch
does not close before 60 seconds expires, the control
will de-energize the inducer for 60 minutes and continue
to flash 2 during the 60 minute inducer off period. After
the inducer has been off for 60 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, low pressure switch, and flame sense.
High pressure switch is ignored.
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 valves (24 VAC) 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 low main gas valve is energized. If
flame is sensed, burners are on and the igniter cools off.
If no flame is sensed, the gas valve closes immediately
and the inducer continues to run. 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
red LED will flash 4 times repetitively. The thermostat
must be opened for at least ten 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 Low main
gas valve energized, inducer motor on High speed for the
first 15 seconds, and begins the heat blower on delay.
Control inputs are continuously monitored while the call
for heat remains. The control will always energize the
gas valve on Low fire with the inducer on high speed for
4. If the pressure measured in step 1 is greater than the
required liquid refrigerant pressure determined in step
3, then there is too much charge in the system. Remove
refrigerant and repeat steps 1 through 3 until the system
is correctly charged.
5. If the pressure measured in step 1 is less than the
required liquid refrigerant pressure determined in step
3, then there is too little charge in the system. Add
refrigerant and repeat steps 1 through 3 until the system
is correctly charged.
Charging an R-410A Unit in Heating Mode
1. Evacuate the refrigerant system.
2. Weigh in the proper charge based on the charge level
noted on the rating plate. Unit charge MUST be verified
in cooling season.
3. Verify the unit is operating properly as outlined in System
Heating.