Carrier 48SS - Manual (Page 24)

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Heating
On a call for heating, terminal “W” of the thermostat is en­
ergized, 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 begins.
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 position, the cool­
ing 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) to condenser (outdoor) fan motor (OEM) Both mo­
tors 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
NOTE. Once the compressor has started and then has stopped,
it should not be started again until 5 minutes have elapsed
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 ther­
mostat “breaks” the circuit between thermostat terminal R
to terminals Y and G These open circuits deenergize con­
tactor 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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