Filter
Top Products
506252-01 Page 7 of 13Issue 0902
OPERATION
Sequence of Operation
Cooling
Upon cooling demand, the thermostat closes circuit R and Y.
Closing R and Y closes the unit contactor, starting the
compressor and outdoor fan. The thermostat automatically
closes R to G circuit which also brings on the indoor blower at
the same time. Upon satisfying cooling demand, the thermostat
will open the above circuits and open the main contactor,
stopping the compressor and outdoor fan. If the unit is equipped
with a delay timer, the blower will continue to operate for 90
seconds which improves system efficiency.
Circulating Air Blower
Depending on the package unit model, the blower motor will
be either a multi-tap PSC motor or a variable speed motor.
PSC Motor
The circulating air blower is controlled by a timing circuit in
the blower control. Timings are not adjustable.
There is no blower “on” delay after a call for heating or
cooling. Blower “off” delay is 90 seconds after the thermostat
is satisfied.
Variable Speed Motor
Units equipped with a variable speed circulation air blower
motor will deliver a constant airflow within a wide range of
external static pressures. Other features of this variable
speed motor include:
ledoM
rotoM
PH
TSUJDA
gnitteS
TAEH
gnitteS
LOOC
gnitteS
MFC
A
MFC
B
MFC
C
MFC
D
lanimoN
gnilooC
UTBk
gnitaeH
eziS
Wk
4201-53/1MRONBB0001008006009
03 01-5 3/1 MRON A A 0001 008 006 009
6351-52/1MRONAA002100010080011
24 02-5 4/3 MRON C C 0081 0061 0041 0021
8402-54/3MRONBB0081006100410021
06 02-5 4/3 MRON A A 0081 0061 0041 0021
Adjusting Airflow (Variable Speed Motor Equipped Units Only)
Table 3
DEHUMIDIFY
CUT TO ENABLE
COOLHEATADJUST
NORM A
B
C
D
A
B
C
D
(+)
(–)
TEST
D1
ADJUST, HEAT,
and COOL Taps
and Dehumidify
Resistor
on Interface
Board
Soft Start/Stop – The variable speed motor will slowly ramp
up to normal operating speed. This minimizes noise and
increases comfort by eliminating the initial blasts of air
encountered with standard motors. At the end of a cooling
or heating cycle, the motor will slowly ramp down.
Circulation Airflow Adjustments – The controls include a
variable speed motor interface board. The ADJUST tap can
be used to raise (+) or lower (–) the airflow by 15%.
Heating and Cooling Airflows – The units are factory set
for the correct heating and cooling airflows. However, airflow
changes can be made by moving the position of the HEAT
and COOL taps (see Table 4).
Continuous Blower – The comfort level of the living space
can be enhanced when using this feature by allowing
continuous circulation of air between calls for cooling or
heating. The continuous circulation of air occurs at half the
full cooling airflow rate. To use this feature, place the
thermostat fan switch into the ON position.
Cooling Airflow Ramp Up – At the beginning of a call for
cooling, the blower will run at 80% of full airflow for 7.5
minutes. This improves the system’s moisture removal and
saves blower power during cooling start.
Reduced Airflow Operation (Dehumidification) – For
situations where humidity control is an issue, the variable
speed motor can be connected to operate at a 25% reduction
in the normal airflow rate. The variable speed motor interface
board provides for connection of a humidistat on the HUM
terminal. When a humidistat is connected, the dehumidifier
resistor on the interface must be cut. The humidistat should
be wired to open during high humidity, which will reduce
blower airflow.