Condensing Unit & Heat Pump R410A Service Manual
111
SERVICING
relay on the defrost board open and turns o the outdoor
fan.
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 connue to run in this mode
unl the defrost cycle is completed.
a. For models with defrost control PCBDM133 or PCBDM160,
a 30 second compressor delay at defrost iniaon/termina-
on is oponal. As shipped from the factory, the control is
set for the delay (“DLY”), which will turn the compressor o
for 30 seconds while the reversing valve shis to/from the
cooling mode posion. To bypass the delay, which typically
reduces sound levels during defrost mode, change the pin
sengs 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 pro-
grammed 10 minute override me the defrost thermostat
is sll closed, the defrost board will automacally 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 o the reversing valve and electric heater(s). The
unit will now be back in a normal heang mode with a heat
pump demand for heang as described in the Heang Oper-
aon in secon 4. See secon 5.4a.
MBE/AEPF WITH TWO STAGE ASX & DSX CONDENSERS
1.0 COOLING OPERATION
When used with the ASX & DSX two stage condensers, 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 “Ylow/Y1” at the condenser. 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 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 sengs
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 operaon.
1.2 If rst stage cooling cannot sasfy 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 operaon and the VSTB will supply 24Vac to “Y/Y2” at
the condenser and the compressor and condenser 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 “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 energized
the “G”, “Y1” and “Y2” demands will be removed.
1.3 When the rst stage cooling demand, “Y1”, is sased,
the room thermostat removes the 24Vac from “G” and
“Y1”. The MBE/AEPF removes the 24Vac from “Ylow/Y1’ at
the condenser and the compressor and condenser fan are
turned o. The blower motor will ramp down to a complete
stop based on the me and rate programmed in the motor.
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 sengs 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 me, if the
heater assembly contains a second heater element, HR1
will contain 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 3rd and 4th heater elements if available. For
the 3rd and 4th 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 rst stage heat demand, “W1” cannot be sased by the
heat pump, the temperature indoors will connue 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 sased,
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 o and the blower motor will change to
low speed. On most digital/electronic thermostats, “W2” will
and then the “W1” and “W2” demands will be removed.
2.3 When the “W1” heat demand is sased, the room
thermostat will remove the 24Vac from “E/W1” and the
VSTB removes the 24Vac from HR1. The contacts on HR1