9
Sequence of Operation
NOTE
: Defrost control board is equipped with 5 minute lockout
timer that is initiated upon any interruption of power.
Turn on power to indoor and outdoor units. Transformer is
energized.
Cooling
On a call for cooling, thermostat makes circuits R--O, R--Y, and
R--G. Circuit R--O energizes reversing valve, switching it to
cooling position. Circuit R--Y sends low voltage through the
safeties and energizes the T1 terminal on the circuit board. If the
compressor
has been off for 5 minutes, or power has not been cycled for 5
minutes, the OF2 relay and T2 terminal will energize. This will
close the contactor, and start the outdoor fan motor and
compressor.
When the cycle is complete, R--Y is turned off, stopping the
compressor and outdoor fan. The 5 minute time guard begins
counting. Compressor will not come on again until this delay
expires. In the event of a power interruption, the time guard will
not allow another cycle for 5 minutes.
NOTE
: If the indoor blower off delay is enabled, it will run up
to an additional 90 seconds to increase system efficiency.
Heating
On a call for heating, thermostat makes circuits R--Y and R--G.
Circuit R--Y sends low voltage through the safeties and energizes
the T1 terminal on the circuit board. T1 energizes the defrost
logic circuit. If the compressor has been off for 5 minutes, or
power
has not been cycled for 5 minutes, the OF2 relay and T2 terminal
will energize. This will close the contactor, start the outdoor fan
motor and compressor.
When the cycle is complete, R--Y is turned off , stopping the
compressor and outdoor fan. The 5 minute time guard begins
counting. Compressor will not come on again until this time
delay expires. In the event of a power interruption, the time guard
will
not allow another cycle for 5 minutes.
Quiet Shift
Quiet shift is a field selectable defrost mode (factory set to OFF),
which will eliminate occasional noise that could be heard at the
start of defrost cycle and restarting of heating cycle. It is selected
by placing DIP switch 3 on defrost board (see Fig. 12) in the ON
position.
When Quiet Shift switch is placed in ON position, and a defrost is
initiated, the following sequence of operation will occur.
Reversing valve will energize, compressor will turn off for 30
seconds, and then turn back on to complete defrost. At the start of
heating after conclusion of defrost, reversing valve will
de--energize, compressor will turn off for another 30 seconds, and
the fan will turn off for 40 seconds, before starting in the heating
mode.
Defrost
The defrost control is a time/temperature control which has field
selectable settings of 30, 60, 90, or 120 minutes, factory set to
90 minutes. These settings represent the amount of time that must
pass after closure of the defrost thermostat before the defrost
sequence begins.
The defrost thermostat senses coil temperature throughout the
heating cycle. When the coil temperature reaches the defrost
thermostat setting of approximately 32 degrees F, it will close,
which energizes the DFT terminal and begins the defrost timing
sequence. When the DFT has been energized for the selected
time, the defrost cycle begins.
Defrost cycle is terminated when defrost thermostat opens, or
automatically after 10 minutes.
Defrost Speedup
To initiate a forced defrost, speedup pins (J1) must be shorted
with a flat head screwdriver for 5 seconds and
RELEASED
. If
the defrost thermostat is open, a short defrost cycle will be
observed (actual length depends on Quiet Shift switch position).
When Quiet Shift is off, only a short 30 second defrost cycle is
observed. With Quiet Shift ON, the speedup sequence is one
minute; 30 second compressor off period followed by 30 seconds
of defrost with compressor operation. When returning to heating
mode, the compressor will turn off for an additional 30 seconds
and the fan for 40 seconds.
If the defrost thermostat is closed, a complete defrost cycle is
initiated. If the Quiet Shift switch is turned on, the compressor
will be turned off for two 30 second intervals as explained
previously.
25H
C
R
