Service Manual

SYSTEM OPERATION
22
IGNITION CONTROL SEQUENCE OF OPERATION
(CONT.)
B. Cooling Operation: High stage cool
Thermostat type is set to two-stage.
Thermostat “Y1” and “Y2” or “Y1”, “Y2” and “G” inputs
initiate high stage cooling.
IDT/ODT/Pressure/Loss of Charge Switch circuits are
checked for closed condition. Cooling operation can
proceed only if these circuits are closed.
1. Low and high stage compressor outputs are ener-
gized.
2. Condenser fan motor is energized at high speed.
3. Air circulating blower is energized at high cool speed
after cool ON delay expires. Cool ON delay timer
begins when thermostat inputs are detected.
Control monitors thermostat, gas valve, flame, and IDT/
ODT/Pressure/Loss of Charge Switches during high
stage cooling operation.
Thermostat “Y1” and “Y2” or “Y1”, “Y2” and “G” inputs
are removed.
Low and high stage compressor outputs are de-ener-
gized.
High speed condenser fan motor is de-energized.
4. Air circulating blower switches to low cool speed for the
cool OFF delay. Cool OFF delay timer begins when
thermostat input is removed.
Control returns to Standby and awaits next thermostat
request.
A. Continuous Fan Operation
1. Thermostat “G” input initiates Continuous Fan opera-
tion.
2. Air circulation blower shall be immediately energized
at the continuous fan speed. For purposes of this
specification, the continuous fan speed shall be the
low heat speed.
3. Thermostat “G” input is removed.
4. Air circulation blower is immediately de-energized.
5. Control returns to Standby and awaits next thermostat
request.
DEFROST CYCLE
NOTE: The defrost board is equipped with a jumper for
SmartShift™ defrost technology operation. This operation
turns the compressor off for 30 seconds at defrost initiation
and termination. The unit is factory shipped for SmartShift™
defrost technology operation. To operate unit at rated effi-
ciencies, move the jumper on the defrost board from “DLY” to
“NORM”.
During operation, the power to the circuit board is controlled
by a temperature sensor, which is clamped to a feeder tube
entering the outdoor coil. Defrost timing periods of 30, 60 and
90 minutes may be selected by setting the circuit board
jumper to 30, 60 and 90 respectively.
Accumulation of time for the timing period selected starts
when the sensor closes (approximately 34°F), and when the
wall thermostat calls for heat. At the end of the timing period,
the unit’s defrost cycle will be initiated provided the sensor
remains closed.
Upon a call for defrost, the blower will continue to run and the
defrost board will send a W1 signal to the ignition control. At
the same time, the compressor will stop for 30 seconds, if the
SmartShift™ defrost technology delay feature is selected on
the defrost board. At this time, the reversing valve shifts from
heat to cool position and condenser fans shut off. The inducer
motor will immediatly energize for a 15 second prepurge.
A 7-second trial for ignition begins by energizing the low and
high stages of the gas valve along with this spark ignition.
Main burners light and control detects presence of flame. The
compressor (after its 30/OFF second delay) restarts in
cooling mode to defrost the condensor coil.
When the sensor opens (approximately 60°F), the defrost
cycle is terminated and the timing period is reset. If the
defrost cycle is not terminated due to the sensor tempera-
ture, a twelve minute override interrupts the unit’s defrost
period. At this time the W1 signal is removed from the ignition
control board, the compressor will stop for a 30 second
SmartShift™ defrost technology delay (if selected) and the
reversing valve slides back to its normal heat position.
A/GPD14