Dwg. No. X730377 P02
Page 9
SEQUENCE OF OPERATION
GENERAL
Operation of the system cooling (and optional heating) cycles is
controlled by the position of the system switch on the room ther-
mostat. Once the system switch is placed in either the HEAT OR
COOL position, unit operation is automatic. The optional automatic
changeover thermostat, when in the AUTO position, automatically
changes to heat or cool with sufficient room temperature change.
With the unit disconnect closed, voltage is supplied to the unit
control transformer and the crankcase heater (if provided). On
single phase units, the crankcase heater is optionally field installed.
COOLING — MECHANICAL COMPRESSOR CYCLE
On a call for mechanical cooling, the indoor fan “G” and the
compressor circuit “Y1” are energized. The indoor fan circuit “G”
starts with power from the control transformer and then energizes
the fan relay coil (F). This closes the fan relay (F) contacts and the
indoor fan motor (IDM) starts.
The compressor circuit starts with power from the control trans-
former through the thermostat switch “Y1” to the compressor
contactor (CC) coil. This closes the (CC) contacts and starts the
compressor (CPR) and the outdoor fan motor (ODM). When the call
for cooling is complete, the compressor contactor (CC), outdoor fan
motor (ODM), and indoor fan relay (F) is de-energized.
HEATING — ELECTRIC HEATERS
On a call for heat, power from the thermostat is received at “W1”,
which energizes the “AH” contactor coil. The “AH” contactor closes
powering the heater, provided all element limits are closed.
If two stages of heat are provided and additional heat is required, the
thermostat’s second stage “W2” circuit is energized powering the
“BH” contactor coil.
NOTE: The indoor thermostat must be configured to provide a “G”
signal to energize the indoor fan relay (F) during the heating mode.
The heater control circuit will not be energized unless the indoor fan
relay (F) is energized.
TROUBLESHOOTING CHART
SYSTEM
FAULTS
ELECTRICAL
REFRIGERANT CIRCUIT
P-PRIMARY CAUSES S-SECONDARY CAUSES
Liquid Pressure Too high
Liquid Pressure Too Low
Suction Pressure Too High
Suction Pressure Too Low
Liquid Refrigerant floodback (TXV System)
Liquid Refrig. floodback (Cap. Tube System)
I. D. Coil Frosting
Compressor Runs Inadequate or No Cooling
Compressor & O.D. fan Do Not Start
Compressor Will Not Start But O.D. Fan Runs
O.D. Fan Won't Start
Compressor Hums But Will Not Start
Compressor Cycles on IOL
I.D. Blower Won't Start
