20
On models equipped with a thermostatic expansion valve, charge
the system to 10º of subcooling. When necessary, adjust the
expansion valve stem for superheat setting.
NOTE: The expansion valve will not need adjustment for most
applications. Check that the system superheat is set between
12ºF and 15ºF after final adjustment.
Superheat Adjustment
1. To adjust superheat, remove the control box cover and locate
the expansion valve on the liquid line of the evaporator.
2. Unscrew the cover from the expansion valve
3. Locate the adjustment screw, and turn it clockwise (in) to
increase superheat or counterclockwise (out) to decrease
superheat.
4. Replace the adjustment cap.
5. Wait a minimum of 10 minutes between adjustments to allow
time for the TXV and pressures to stabilize.
Cooling Operation
NOTE: Mechanical cooling cannot be reliably provided at
ambient temperatures below 50°F (10ºC).
1. Turn on the electrical power supply to the unit.
2. Place the room thermostat selector switch in the COOL
position (or AUTO if available, and if automatic changeover
from cooling to heating is desired).
3. Set the room thermostat to the desired temperature.
SEQUENCE OF OPERATION
Heating System
This unit is equipped with an ignition control that automatically
lights the main burner.
NOTE: Do not attempt to light the main burners by any other
method.
1. Thermostat calls for low-stage or high-stage heating.
2. The induced draft blower energizes for a 15-second pre-
purge.
3. The spark igniter and low-stage and high-stage gas control
valves energizes for 7 seconds.
NOTE: The igniter produces a very intense electrical spark that
ignites the gas.
4. The main burners light, and the control detects the presence
of a flame.
5. If the call is for low-stage heat, the induced draft blower
switches to low speed and the high-stage gas control valve
closes 5 seconds after the main burners light. If the call is for
high-stage heat, the induced draft blower remains at high
speed and the high-stage gas control valve remains open.
NOTE: If a single-stage thermostat is used, the control will
step to low stage after the main burners light and remain at
low stage for 5 or 10 minutes, depending on the jumper
position. If the call for heat remains after the transition delay
time expires, the control will transition from low stage to high
stage.
6. The 30-second Heat Fan On delay time begins after the main
burners light.
7. The unit delivers heat to the conditioned space until the
thermostat is satisfied.
8. The gas control valve(s) de-energizes.
9. The induced draft blower continues operation for a
30-second post-purge.
10. The induced draft blower remains at low speed (or switches
from high to low, if operating at high stage heat) for the
30-second post-purge.
11. Ignition control begins timing the Heat Fan Off delay.
There is an adjustable Heat Fan Off delay of approximately
90/120/150/180 seconds (factory set at 150). If the unit is
operating at high stage when the call for heat is removed, the
blower will operate for 30 seconds at high-heat speed, and
then switch to low-heat speed for the remainder of the
selected Heat Fan Off delay.
After the Heat Fan Off delay time has elapsed, the induced
draft blower will de-energize. This allows any additional heat
in the heat exchanger to be transferred to the conditioned
space.
Cooling System
1. The thermostat calls for low- or high-stage cooling.
2. If the thermostat call is for low-stage cooling, the compressor
and outdoor fan are energized at low stage. If the thermostat
call is for high-stage cooling, the compressor and outdoor fan
are energized at high-stage cooling.
3. Approximately 6 seconds later, the indoor blower fan will
energize.
4. The unit will deliver cooling to the conditioned space until the
thermostat is satisfied.
5. The compressor and outdoor fan will be de-energized when
the thermostat opens.
6. The indoor blower fan continues to run at low-cool speed for
approximately 60 seconds after the thermostat is satisfied.
This allows additional cooling from the indoor coil to be
transferred to the conditioned space. Then, the indoor blower
fan is de-energized.
NOTE: A 180-second anti-short cycle is integral to the control
and prevents recycling of the compressor.
