Condensing Unit & Heat Pump R410A Service Manual
109
SERVICING
heat pump is turned o and the blower motor turns o aer
a 65 second o delay.
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.
5.1 The heat pump will be on and operang in the heang
mode as described the Heang Operaon in secon 4.
5.2 The defrost control in the heat pump unit checks to seeif a
defrost is needed every 30, 60 or 90 minutes of heat pump
operaon depending on the selectable seng by monitoring
the state of the defrost thermostat aached to the outdoor
coil.
5.3 If the temperature of the outdoor coil is low enough to
cause the defrost thermostat to be closed when the defrost
board checks it, the board will iniate a defrost cycle.
5.4 When a defrost cycle is iniated, the contacts of the HVDR
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 contactson 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 will close to start the outdoor fan and the con-
tacts 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 Operaon in secon 4. See
secon 5.4a.
MBE ELECTRONIC BLOWER TIME DELAY RELAY
AEPF AIR HANDLER
SEQUENCE OF OPERATION
This document covers the basic sequence of operaon for a
typical applicaon with a mercury bulb thermostat. When a
digital/electronic thermostat is used, the on/o staging of the
auxiliary heat will vary. Refer to the installaon instrucons and
wiring diagrams provided with the MBE/AEPF for specic wiring
connecons, dip switch sengs and system conguraon.
MBE/AEPF WITH SINGLE STAGE GSX, ASX, SSX, and VSX CONDENSERS
When used with a single stage GSX, SSX, ASX, and VSX
condensers, dip switch #4 must be set to the on posion on the
VSTB inside the MBE/AEPF. The “Y” 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” 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 “Y” and 24Vac is supplied to “G” and “Y/Y2” of the
MBE/AEPF unit. The VSTB inside the MBE/AEPF will turnon
the blower motor and the motor will ramp up to 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
condenser and the compressor and condenser are turned
on.
1.2 When the cooling demand is sased, the room thermo-
stat removes the 24Vac from “G” and “Y”. The MBE/AEPF
removes the 24Vac from “Y’ at the condenser and the com-
pressor 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 ther-