Sequence Of Operation - Lennox CBA25UHV-018 Unit Information

Sequence of Operation

COOLING (COOLING ONLY OR HEAT PUMP)
When the thermostat calls for cooling, 24 volts is put on
the blower time-delay relay coil and then the indoor blow-
er relay energizes. The normally open contacts close,
causing the indoor blower motor to operate. The circuit
between R and Y is completed, closing the circuit to the
contactor in the outdoor unit, starting the compressor and
outdoor fan motor.
On heat pumps, circuit R and O energizes the reversing
valve, switching the valve to the cooling position. (The re-
versing valve remains energized as long as the thermo-
stat selector switch is in the COOL position.)
At the completion of the cooling demand, the indoor blow-
er and outdoor unit should cycle off. Air handler should
cycle off 45 seconds after the outdoor unit shuts off.
HEATING (ELECTRIC HEAT ONLY)
When the thermostat calls for heat, the circuit between R
and W is completed, and the heat sequencer is energized.
A time delay follows before the heating elements and the
indoor blower motor come on. Units with a second heat
sequencer can be connected with the first sequencer to W
on the thermostat subbase, or they may also be connect-
ed to a second stage on the subbase.
HEATING (HEAT PUMP)
When the thermostat calls for heating, 24 volts is put on
the blower time-delay relay coil. Then normally open con-
tacts close, causing the indoor blower motor to operate.
The circuit between R and Y is completed, closing the cir-
cuit to the contactor in the outdoor unit, starting the com-
pressor and outdoor fan motor.
If the room temperature should continue to fall, the cir-
cuit between R and W1 is completed by the second-stage
heat room thermostat. Circuit R-W1 energizes a heat se-
quencer. The completed circuit will energize supplemen-
tal electric heat (if applicable). Units with a second heat
sequencer can be connected with the first sequencer to
W1 on the thermostat. They may also be connected to a
second heating stage W2 on the thermostat subbase.
EMERGENCY HEAT (HEATING HEAT PUMP)
If the selector switch on the thermostat is set to the emer-
gency heat position, the heat pump will be locked out of
the heating circuit, and all heating will be electric heat (if
applicable). A jumper should be placed between W2 and E
on the thermostat subbase so that the electric heat control
will transfer to the first-stage heat on the thermostat. This
will allow the indoor blower to cycle on and off with the
electric heat when the fan switch is in the AUTO position.
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