Service Instructions

SERVICING
108
The contacts of the LVDR relay on the defrost board closes
and supplies 24Vac to “O” and “W2”. The reversing valve is
energized and the contacts on HR1 close and turns on the
electric heater(s). The unit will continue to run in this mode
until the defrost cycle is completed.
a. For models with defrost control PCBDM133 or PCBDM160,
a 30 second compressor delay at defrost initiation/termi-
nation is optional. As shipped from the factory, the control
is set for the delay (“DLY”), which will turn the compressor
off for 30 seconds while the reversing valve shifts to/from
the cooling mode position. To bypass the delay, which
typically reduces sound levels during defrost mode, change
the pin settings from “DLY” to “NORM”.
5.5 When the temperature of the outdoor coil rises high enough
to causes the defrost thermostat to open, the defrost cycle
will be terminated. If at the end of the programmed 10 minute
override time the defrost thermostat is still closed, the
defrost board will automatically terminate the defrost cycle.
5.6 When the defrost cycle is terminated, the contacts of the HVDR
relay on the defrost board will close to start the outdoor fan
and the contacts of the LVDR relay will open and turn off the
reversing valve and electric heater(s). The unit will now be
back in a normal heating mode with a heat pump demand for
heating as described in the Heating Operation in section 4.
See section 5.4a.
MBE/AEPF WITH TWO STAGE ASX & DSX CONDENSERS
1.0 COOLING OPERATION
When used with the ASX & DSX two stage condensers, 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 “Out-
door Unit” must be connected to “Ylow/Y1” at the condenser.
The “Y2” output from the indoor thermostat must be con-
nected 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 condenser. The orange jumper
wire from terminal “Y1” to terminal “O” on the VSTB inside
the MBE/AEPF must remain connected.
1.1 On a demand for cooling, the room thermostat energizes “G”
and “Y1” and 24Vac is supplied to “G” and “Ylow/Y1” of the
MBE/AEPF unit. The VSTB inside the MBE/AEPF 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 “Ylow/Y1” at
the condenser and the compressor and condenser fan starts
in low speed operation.
1.2 If first stage cooling cannot satisfy the demand, the room
thermostat will energize “Y2” and supply 24Vac to the MBE/
AEPF unit. The blower motor will change to the cfm for high
speed operation and the VSTB will supply 24Vac to “Y/Y2” at
the condenser and the compressor and condenser 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 “Y/Y2” at the condenser.
The blower will drop to 60% of the programmed cfm and the
compressor and condenser fan will change to low speed. On
most digital/electronic thermostats, “Y2” will remain ener-
gized until the first stage cooling demand “Y1” is satisfied and
then the “G”, “Y1” and “Y2” demands will be removed.
1.3 When the first stage cooling demand, “Y1”, is satisfied, the
room thermostat removes the 24Vac from “G” and “Y1”. The
MBE/AEPF removes the 24Vac from “Ylow/Y1’ at the con-
denser and the compressor and condenser fan are turned off.
The blower motor will ramp down to a complete stop based
on the time and rate programmed in the motor.
2.0 Heating Operation
2.1 On a demand for heat, the room thermostat energizes “W1”
and 24Vac is supplied to terminal “E/W1” of the VSTB inside
the MBE/AEPF unit. The VSTB will turn on the blower motor
and the motor will ramp up to the speed programmed in the
motor based on the settings for dip switch 1 and 2. The VSTB
will supply 24Vac to heat sequencer HR1 on the electric
heater assembly.
2.2 HR1 contacts M1 and M2 will close within 10 to 20 seconds
and turn on heater element #1. At the same time, if the heater
assembly contains a second heater element, HR1 will con-
tain a second set of contacts, M3 and 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 3
rd
and 4
th
heater elements if available. 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.