Bulletin 30-20 — Page 21
© Copyright 2010, Unico, Inc.
STARTUP
! IMPORTANT !
The most important step when installing
the Unico System is making sure it has
the correct airflow. Be sure to record the
amperage and voltage of every system in
order to verify the airflow through the unit.
Also, measure the airflow at each outlet to
verify the airflow in each room. Both me-
thods are described later in this section.
Sequence of Operation
The sequence of operation depends greatly on the op-
tions installed and type of control thermostat used. Most
thermostats have a fan AUTO-ON switch. When the fan
switch is set to ON, the “G” circuit is closed and the
blower relay is energized. The indoor blower starts after
about a 20 second delay. The following paragraphs de-
scribe the sequence of operation when the fan is set to
AUTO. If the fan switch is set to ON, the sequence is the
same except the “G” circuit is always closed and the
indoor fan is always operating.
Cooling Cycle (A/C or Heat Pump). When the
thermostat calls for cooling, the “Y” and the “G” circuits
are closed, and a 24 V signal is sent to the compressor
contactor in the outdoor unit and fan relay in the indoor
unit. After about 20 seconds, the indoor blower starts. At
the same time, the compressor and outdoor fan also start.
Depending on the control circuitry in the outdoor unit,
there may be a time delay before the outdoor unit starts.
If the system was just turned off, the time delay could be
as much as five minutes. The cooling system is now op-
erating.
For heat pump thermostats setting the switch to ‘cooling’
immediately closes the “O” circuit, which is used to
energize the reversing valve solenoid if required by the
heat pump. Otherwise, the “B” circuit, which closes
when switched in heating, is used to energize the revers-
ing valve solenoid. (Refer to the heat pump manufactur-
er’s instructions to see which mode the solenoid needs to
be energized – whether in heating or cooling.)
When the thermostat is satisfied, the 24 V signals are
opened and the outdoor unit stops. The indoor blower
continues to operate for about 40 seconds, then stops.
The system is now off.
Heating Cycle (Heat Pump). Setting the thermostat
to HEATING will automatically switch the reversing
valve solenoid. This setting closes the “B” circuit which
sends a 24V signal to energize the solenoid if required
by the heat pump. Otherwise the “B” circuit is not used
and the solenoid is not energized during heating.
When the thermostat calls for heating, the “Y” and “G”
circuits are closed, sending a 24 V signal to the compres-
sor contactor in the outdoor unit and the fan relay in the
indoor unit. This starts the indoor blower and the out-
door compressor. There is a time delay of about 20
seconds for the indoor unit. The heating system is now
operating in stage one.
If the first stage does not satisfy the thermostat, the
second stage thermostat calls for more heat. This closes
the “W2” contacts and energizes the sequencer for elec-
tric heat (if installed). When the second stage thermostat
is satisfied, the “W2” circuit is broken and the sequencer
is de-energized. The electric heating system is now off.
When the first stage thermostat is satisfied, the 24 V
signals are opened and the outdoor unit stops. The in-
door blower continues to operate for about 40 seconds,
then stops. The system is now off.
Heating Cycle (Electric Heat-Only). When the
thermostat calls for heating, the “W” and “G” circuits
are closed. The W circuit completes the 24V signal to
the sequencer in the electric duct heater, which cycles on
the electric heating elements. The G circuit completes
the 24V signal to the fan relay in the indoor unit, which
starts the indoor blower after a time delay of about 20
seconds. The heating system is now operating.
When the thermostat is satisfied, the 24 V signals are
opened and the indoor blower stops after about 40
seconds. At the same time the sequencer cuts the power
to the electric elements. The system is now off.
Note: Use a thermostat designed for electric
heat. A normal heating-cooling thermostat will
not close the “G” circuit on heating.
Ventilation Cycle. When the thermostat is satisfied
and the fan switch is set to “AUTO”, the “G” circuit is
open so that power to the motor goes through the varia-
ble speed controller and the motor runs at reduced speed.
The speed controller is set by the installer to a specific
speed. (The factory default setting for the speed control
is “OFF”.)
Using the typical wiring schematic, the fan will operate
continuously if the variable speed control is switched on.
It will either operate at normal speed (full speed) or at a
reduced speed. Use the alternate wiring diagram to allow
the user to turn the ventilation mode off at the thermos-
tat. To turn it off simply move the fan switch to the
AUTO position.
Checking Air Flow
CAUTION
Do not operate blower with free dis-
charge or low static pressures (below 1-
inch w.c. (250 Pa)) to prevent motor
from overloading.
After the system is installed and before charging system,
check for proper airflow. Record the position of the re-
strictor plate, the plenum static pressure, and the motor
amperage. With this information, the amount of airflow
can be determined.
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