Condensing Unit & Heat Pump R410A Service Manual

109
SERVICING
heat pump is turned o and the blower motor turns o aer
a 65 second o delay.

On heat pump units, when the room thermostat is set to the
heang mode, the reversing valve is not energized. As long as
the thermostat is set for heang, the reversing valve will be in
the de-energized posion for heang except during a defrost
cycle.
5.1 The heat pump will be on and operang in the heang
mode as described the Heang Operaon in secon 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
operaon depending on the selectable seng by monitoring
the state of the defrost thermostat aached 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 iniate a defrost cycle.
5.4 When a defrost cycle is iniated, 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 connue to run in this
mode unl the defrost cycle is completed.
a.For models with defrost control PCBDM133 or PCBDM160,
a 30 second compressor delay at defrost iniaon/termina-
on is oponal. 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 shis to/from the
cooling mode posion. To bypass the delay, which typically
reduces sound levels during defrost mode, change the pin
sengs 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 sll closed, the defrost board will automacally 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 heang mode with a heat pump demand for heang
as described in the Heang Operaon in secon 4. See
secon 5.4a.

MBE ELECTRONIC BLOWER TIME DELAY RELAY
AEPF AIR HANDLER
SEQUENCE OF OPERATION
This document covers the basic sequence of operaon for a
typical applicaon 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 installaon instrucons and
wiring diagrams provided with the MBE/AEPF for specic wiring
connecons, dip switch sengs and system conguraon.
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 posion 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 sengs 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 sased, 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 sengs 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 sased by the
heat pump, the temperature indoors will connue 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 sased,
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 sased, the room ther-