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SERVICING
57
For the 3
rd
and 4
th
heater elements to operate on a
second stage heat demand, the PJ4 jumper on the VSTB
inside the MBE/AEPF must be cut. With the PJ4 jumper
cut, the VSTB will run the blower motor on low speed on a “W1”
only demand. If the first stage heat demand, “W1” cannot be
satisfied by the heat pump, the temperature indoors will
continue to drop. The room thermostat will then energize “W2”
and 24Vac will be supplied to HR2 on the heater assembly and
the blower motor will change to high speed. When the “W2”
demand is satisfied, the room thermostat will remove the
24Vac from “W2” and the VSTB will remove the 24Vac from
HR2. The contacts on HR2 will open between 30 to 70
seconds and heater elements #3 and #4 will be turned off and
the blower motor will change to low speed. On most digital/
electronic thermostats, “W2” will remain energized
until the first stage demand “W1” is satisfied and then
the “W1” and “W2” demands will be removed.
2.3 When the “W1” heat demand is satisfied, the room
thermostat will remove the 24Vac from “E/W1” and the
VSTB removes the 24Vac from HR1. The contacts on
HR1 will open between 30 to 70 seconds and turn off the
heater element(s) and the blower motor ramps down to a
complete stop.
MBE/AEPF WITH TWO STAGE ASZ & DSZ HEAT PUMP
UNITS
3.0 Cooling Operation
When used with the ASZ & DSZ two stage heat
pumpS, dip switch #4 must be set to the OFF position
on the VSTB inside the MBE/AEPF. The “Y1” output
from the indoor thermostat must be connected to the
purple wire labeled “Ylow/Y1” inside the wire bundle
marked “Thermostat” and the purple wire labeled “Ylow/
Y1” inside the wire bundle marked “Outdoor Unit” must be
connected to “Y” at the heat pump. The “Y2” output from
the indoor thermostat must be connected to the yellow
wire labeled “Y/Y2” inside the wire bundle marked “Ther-
mostat” and the yellow wire labeled “Y/Y2” inside the wire
bundle marked “Outdoor Unit” must be connected to “Y/
Y2” at the heat pump. The orange jumper wire from
terminal “Y1” to terminal “O” on the VSTB inside the
MBE/AEPF must be removed.
On heat pump units, when the room thermostat is set to the
cooling mode, 24Vac is supplied to terminal “O” of the
VSTB inside the MBE unit. The VSTB will supply 24Vac
to “O” at the heat pump to energize the reversing valve. As
long as the thermostat is set for cooling, the reversing
valve will be in the energized position for cooling.
3.1 On a demand for cooling, the room thermostat energizes
“G” and “Y1” and 24Vac is supplied to “G” and “Ylow/Y1”
of the MBE unit. The VSTB inside the MBE will turn on
the blower motor and the motor will ramp up to 60% of the
speed programmed in the motor based on the settings for
dip switch 5 and 6. The VSTB will supply 24Vac to “Y” at
the heat pump and the compressor and outdoor fan starts
in low speed operation.
3.2 If first stage cooling cannot satisfy the demand, the room
thermostat will energize “Y2” and supply 24Vac to “Y/
Y2”of the MBE unit. The blower motor will change to the
cfm for high speed operation and the VSTB will supply
24Vac to “Y2” at the heat pump. The compressor and
outdoor fan will change to high speed operation. When
the “Y2” demand is satisfied, the thermostat will remove
the “Y2” demand and the VSTB will remove the 24Vac
from “Y2” at the heat pump. The blower will drop to 60%
of the programmed cfm and the compressor and outdoor
fan will change to low speed operation. On most digital/
electronic thermostats, “Y2” will remain energized
until the first stage cooling demand “Y1” is satisfied
and then the “G”, “Y1” and “Y2” demands will be
removed.
3.3 When the first stage cooling demand, “Y1”, is satisfied,
the room thermostat removes the 24Vac from “G” and
“Y1”. The VSTB removes the 24Vac from “Y’ at the heat
pump and the compressor and outdoor fan are turned off.
The blower motor will ramp down to a complete stop
based on the time and rate programmed in the motor.
4.0 Heating Operation
On heat pump units, when the room thermostat is set to
the heating mode, the reversing valve is not energized.
As long as the thermostat is set for heating, the reversing
valve will be in the de-energized position for heating
except during a defrost cycle. Some installations may
use one or more outdoor thermostats to restrict the
amount of electric heat that is available above a preset
ambient temperature. Use of optional controls such as
these can change the operation of the electric heaters
during the heating mode. This sequence of operation
does not cover those applications.
4.1 On a demand for first stage heat with heat pump units,
the room thermostat energizes “G” and “Y1” and 24Vac
is supplied to “G” and “Ylo/Y1” of the MBE/AEPF. The
VSTB will turn on the blower motor and the motor will
ramp up to 60% of the speed programmed in the motor
based on the settings of dip switch 1 and 2. The VSTB
will supply 24Vac to “Y” at the heat pump. The
compressor will start on high speed and outdoor
fan will start on low speed on a “Y1” heating
demand but the blower motor will deliver only 60%
of the programmed cfm for high speed heating
operation.
4.2 If a thermostat that provides a “Y2” demand in heating is
used and first stage heating cannot satisfy the demand,
the room thermostat will energize “Y2” and supply
24Vac to “Y/Y2” of the MBE unit. The blower motor will
change to the cfm for high speed heating operation and
the VSTB will supply 24Vac to “Y/Y2” at the heat pump.