20
CONTROLS
Operating sequence
Cooling — When the system thermostat calls for cooling, 24 V is
supplied to the “Y” and “G” terminals of the thermostat. This
completes the circuit to the contactor coil (C) and indoor
(evaporator) fan relay (IFR). The normally open contacts of
energized C close and complete the circuit through compressor
motor (COMP) to outdoor (condenser) fan motor (OFM). Both
motors start instantly. The set of normally open contacts of
energized IFR close and complete the circuit through IFM. The
IFM starts instantly.
On the loss of the thermostat call for cooling, 24 V is removed
from both the “Y” and “G” terminals (provided the fan switch is in
the “AUTO” position) de--energizing the compressor contactor and
opening the contacts supplying power to compressor/OFM. After a
90--second delay, the IFM shuts off. If the thermostat fan selector
switch is in the “ON” position, the IFM will run continuously. For
the 460 V units there is a step down autotransformer supplying 230
V to the Indoor Fan Motor.
NOTE: On units with a Time Guard
®
II device: Once the
compressor has started and then stopped, it cannot be restarted
again until 5 minutes have elapsed.
Heating — If accessory electric heaters are installed, on a call for
heat, circuit R--W is made through the thermostat contacts. Circuit
R--G is made which energizes the IFR. If the heaters are staged,
then the thermostat closes a second set of contacts (W2) when
second stage is required. When thermostat is satisfied, contacts
open, deenergizing the heater relay and the IFR.
50GL--A
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