Controls
Sequence of operation
Heating — On a call for heating, terminal ‘‘W’’ of the ther-
mostat is energized, starting the induced-draft motor. When
the hall-effect sensor on the induced-draft motor senses that
it has reached the required speed, the burner sequence be-
gins. This function is performed by the integrated control
board (IGC). The indoor-fan motor is energized 45 seconds
after flame is established. When the thermostat is satisfied
and ‘‘W’’ is deenergized, the indoor-fan motor stops after a
45-second time-off delay.
Cooling — With the room thermostat SYSTEM switch in
the COOL position and the FAN switch in the AUTO. po-
sition, the cooling sequence of operation is as follows:
When the room temperature rises to a point that is slightly
above the cooling control setting of the thermostat, the ther-
mostat completes the circuit between thermostat terminal
R to terminals Y and G. These completed circuits through
the thermostat connect contactor coil (C) (through unit wire
Y) and blower relay coil (BR) (through unit wire G) across
the 24-v secondary of transformer (TRAN).
The normally-open contacts of energized contactor (C)
close and complete the circuit through compressor motor
(COMP) and condenser (outdoor) fan motor (OFM). Both
motors start instantly.
The set of normally-open contacts of energized relay BR
close and complete the circuit through evaporator blower
(indoor) fan motor (IFM). The blower motor starts
instantly.
The cooling cycle remains ‘‘on’’ until the room tempera-
ture drops to point that is slightly below the cooling
control setting of the room thermostat. At this point, the
thermostat ‘‘breaks’’ the circuit between thermostat termi-
nal R to terminals Y and G. These open circuits deenergize
contactor coil C and relay coil BR. The condenser and com-
pressor motors stop. After a 30-second delay, the blower
motor stops. The unit is in a ‘‘standby’’ condition, waiting
for the next ‘‘call for cooling’’ from the room thermostat.
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