Lennox 16HPX Series, Unit Information

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Page 31
16HPX OPERATING SEQUENCE
This is the sequence of operation for 16HPX series units.
The sequence is outlined by numbered steps which cor-
respond to circled numbers on the adjacent diagram. The
steps are identical for both cooling and first stage heat -
ing demand with the exception reversing valve L1 is en -
ergized during cooling demand and de-energized during
heating demand.
NOTE –
Transformer in indoor unit supplies power (24
VAC) to the thermostat and outdoor unit controls.
COOLING:
Internal thermostat wiring energizes terminal O by cooling
mode selection, energizing the reversing valve L1.
1 - Demand initiates at Y1 in the thermostat.
2 - 24VAC energizes compressor contactor K1.
3 - K1-1 N.O. closes, energizing compressor (B1) and
outdoor fan motor (B4).
END OF COOLING DEMAND:
4 - Demand is satisfied. Terminal Y1 is de-energized.
5 - Compressor contactor K1 is de-energized.
6 - K1-1 opens and compressor (B1) and outdoor fan
motor (B4) are de-energized and stop immediately.
FIRST STAGE HEAT:
Internal thermostat wiring de-energizes terminal O by
heating mode selection, de-energizing the reversing valve
L1.
See steps 1, 2 and 3.
End of FIRST STAGE HEAT:
See steps 4, 5 and 6.
DEFROST MODE:
When a defrost cycle is initiated, the control energizes
the reversing valve solenoid and turns off the condenser
fan. The control will also put 24VAC on the “W1” (auxil -
iary heat) line. The unit will stay in this mode until either
the coil sensor temperature is above the selected termi-
nation temperature, the defrost time of 14 minutes has
been completed, or the room thermostat demand cycle
has been satisfied. (If the temperature select shunt is not
installed, the default termination temperature will be 90°F.)
If the room thermostat demand cycle terminates the cycle,
the defrost cycle will be held until the next room thermo -
stat demand cycle. If the coil sensor temperature is still
below the selected termination temperature, the control
will continue the defrost cycle until the cycle is terminated
in one of the methods mentioned above. If a defrost is ter-
minated by time and the coil temperature did not remain
above 35°F (2°C) for 4 minutes the control will go to the
30-minute Time/Temperature mode.
Servicing Units Void of Charge
If the outdoor unit is void of refrigerant, clean the system
using the procedure described below.
1 - Leak check system using procedure outlined on
page 15.
2 - Evacuate the system using procedure outlined on
page 16.
3 - Use nitrogen to break the vacuum and install a new
filter drier in the system.
4 - Evacuate the system again using procedure
outlined on page 16.
5 - Weigh in refrigerant.
Start-Up
IMPORTANT
If unit is equipped with a crankcase heater, it should
be energized 24 hours before unit start-up to prevent
compressor damage as a result of slugging.
1 - Rotate fan to check for binding.
2 -
Inspect all factory and field-installed wiring for loose
connections.
3 - After evacuation is complete, open the liquid line
and suction line service valves to release the
refrigerant charge (contained in outdoor unit) into
the system.
4 - Replace the stem caps and tighten as specified in
Operating Service Valves on page 7.
5 - Check voltage supply at the disconnect switch. The
voltage must be within the range listed on the unit's
nameplate. If not, do not start the equipment until
you have consulted with the power company and
the voltage condition has been corrected.
6 - Set the thermostat for a cooling demand. Turn
on power to the indoor indoor unit and close the
outdoor unit disconnect switch to start the unit.
7 - Recheck voltage while the unit is running. Power
must be within range shown on the nameplate.
8 - Check system for sufficient refrigerate by using
the procedures listed under Start-Up and Charging
Procedures.
9 - Recheck voltage while the unit is running. Power
must be within range shown on the nameplate.