Condensing Unit & Heat Pump R410A Service Manual
112
SERVICING
will open between 30 to 70 seconds and turn o the heater
element(s) and the blower motor ramps down to a complete
stop.
MBE/AEPF WITH TWO STAGE ASZ & DSZ HEAT PUMP UNITS
When used with the ASZ & DSZ two stage heat pumps, dip
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
“Thermostat” 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 posion 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 sengs 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 operaon.
3.2 If rst stage cooling cannot sasfy 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 operaon and the VSTB will supply 24Vac to “Y2”
at the heat pump. The compressor and outdoor fan will
change to high speed operaon. When the “Y2” demand is
sased, 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
operaon. On most digital/electronic thermostats, “Y2” will
be removed.
3.3 When the rst stage cooling demand, “Y1”, is sased, 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 o. The blower
motor will ramp down to a complete stop based on the me
and rate programmed in the motor.
On heat pump units, when the room thermostat is set to the
heang mode, the reversing valve is not energized. As long
as the thermostat is set for heang, the reversing valve will
be in the de-energized posion for heang except during a
defrost cycle. Some installaons may use one or more outdoor
thermostats to restrict the amount of electric heat
that is available above a preset ambient temperature. Use of
oponal controls such as these can change the operaon of
the electric heaters during the heang mode. This sequence of
operaon does not cover those applicaons.
4.1 On a demand for rst 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 sengs of dip switch 1 and 2. The VSTB will supply
24Vac to “Y” at the heat pump. The compressor will start
on low stage and outdoor fan will start on low speed on
4.2 If a thermostat that provides a “Y2” demand in heang is
used and rst stage heang cannot sasfy 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 heang operaon and the VSTB will sup-
ply 24Vac to “Y/Y2” at the heat pump. The outdoor fan will
change to high speed operaon and compressor will shi to
high stage. If the “Y2” demand is present and becomes sat-
ised, the thermostat will remove the “Y2” demand and the
VSTB will remove the 24Vac from “Y/Y2” at the heat pump.
The blower will drop to 60% of the programmed cfm and
the outdoor fan will change to low speed. On most digital/
electronic thermostats, “Y2” will remain energized unl the
rst stage heang demand “Y1” is sased and then the “G”,
“Y1” and “Y2” demands will be removed.
4.3 If the heat pump operaon cannot sasfy the demand, the
room thermostat energizes “W2/W3” and 24Vac is supplied
to terminal “E/W1” of the VSTB inside the MBE/AEPF unit.
The VSTB will supply 24Vac to heat sequencer HR1 on the
electric heater assembly.
4.4 HR1 contacts M1 and M2 will close within 10 to 20 seconds
and turn on heater element #1. At the same me, if the
heater assembly contains a second heater element, HR1
will contain a second set of contacts, M3and M4, which will
close and turn on heater element #2.
Note: If more than two heater elements are on the heater
assembly, it will contain a second heat sequencer, HR2, which
will control the 3rd and 4th heater elements if available. For the
3rd and 4th heater elements to operate on a second stage
auxiliary heat demand, the PJ4 jumper on the VSTB inside
the MBE/AEPF must be cut. If the “W2/W3” demand cannot
be sased by the heat pump, the temperature indoors will
connue to drop. The room thermostat will then energize “W3/
W4” and 24Vac will be supplied to “W/W2” of the MBE. The
VSTB will supply 24Vac to HR2 on the electric heater assembly.
When the “W3/W4” demand is sased, the room thermostat
will remove the 24Vac from “W/W2” of the MBE/AEPF. The
contacts on HR2 will open between 30 to 70 seconds and