58
Operation
Unit operations should be controlled with
thermostat or unit controller, never at the
main power supply, except for emergency or
complete shutdown of the unit.
Thermostat Operation
Heating
Thermostat system switch - "Heat"
Thermostat fan switch - "Auto" or "On"
Thermostat temperature set to desired point.
Cooling
Thermostat system switch - "Cool"
Thermostat fan switch - "Auto" or "On"
Thermostat temperature set to desired point.
Air Circulation
Thermostat system switch - "Off"
Thermostat fan switch - "Auto" or "On"
No change of the thermostat temperature.
With these settings, the supply blower will
run continuously but the supply air will not
be heated, cooled, or dehumidified.
System Off
Thermostat system switch - "Off"
Thermostat fan switch - "Auto"
No change of the thermostat temperature.
With these settings the system is shut down,
with the exception of control system power.
Night and Weekend Unoccupied Operation
To reduce the operating time of the unit when
the space is unoccupied, such as nights and
weekends, it is recommended that the
temperature setting be raised about 5°F while
unoccupied during the cooling season and
lowered about 10°F during the heating
season.
Split System DX Cooling Operation and
Control
When a call for cooling (G and Y1, Y2, etc.)
is made the supply blower motors and
compressors will energize.
Chilled Water or Non-Compressorized
DX Cooling Operation
Valve controls for chilled water cooling coil
and non-compressorized DX coil are by
others.
Steam or Hot Water Preheating
Operation
Valve control for steam and hot water heating
coils are by others. Heating is accomplished
by passing steam or hot water through the
steam or hot water coil assembly.
Electric Heating Operation
When a call for heating (G and W1, W2, etc.)
is made the supply fan motors and electric
resistance heaters will energize. Heating is
accomplished by passing electrical current
through a specified amount of resistance
heaters which will produce the required heat.
On a fault condition the main limit located in
the supply air or the auxiliary limit located
downstream the supply blower will remove
power from all contactors.
Gas Heater Operation
When heat (G and W1, W2, etc.) is called for
the combustion motor starts and the ignition
control is energized. The control sends 24
VAC to the main gas valve and high voltage
to the igniter. If a burner flame has been
detected within 10 seconds, the spark is
extinguished and the flame continues. If a
flame has not been detected after 10 seconds,
the gas valve closes, the spark ceases and the
induced draft blower continues to purge the
heat exchanger. After 45 seconds of purge,
the ignition system will attempt to light the
burners again. Should no flame be detected
after 3 tries, the ignition control will lock out
the system. Power to the ignition control
must be cycled to reset the heater control.
On a fault, the gas train is shut down by a
main limit located in the heat exchanger area
or by an auxiliary limit sensing the
temperature after the supply fan.
