Condensing Unit & Heat Pump R410A Service Manual

108
SERVICING
“G” and “Y” and 24Vac is supplied to “Y” at the condensing
unit and the “G” terminal on the EBTDR board.
1.2 The compressor and condenser fan are turned on and aer
a 7 second on delay, the relay on the EBTDR board is ener-
gized and the blower motor starts.
1.3 When the cooling demand “Y” is sased, the room ther-
mostat removes the 24Vac from “G” and “Y”.
1.4 The compressor and condenser fan are turned o and aer
a 65 second delay o, the relay on the EBTDR board is de-en-
ergized and the blower is turned o.

2.1 On a demand for heat, the room thermostat energizes
“W1” and 24Vac is supplied to heat sequencer, HR1, on the
heater assembly.
2.2 The contacts M1 and M2 will close within 10 to 20 sec-
onds and turn on heater element #1. The normally closed
contacts on the EBTDR are also connected to terminal M1.
When M1 and M2 close, the blower motor will be energized
thru the normally closed contacts on the EBTDR board. 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 to 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. 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. When the “W2” demand is
sased, the room thermostat 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. On most digital/


“W2” demands will be removed.
2.3 When the “W1” heat demand is sased, the room ther-
mostat will remove the 24Vac from HR1. Both set of con-
tacts on the relay opens within 30 to 70 seconds and turn o
the heater element(s) and the blower motor.
MBR/AR*F WITH SINGLE STAGE HEAT PUMPS

On heat pump units, when the room thermostat set to the
cooling mode, 24Vac is supplied to “O” which energizes the
reversing valve. As long as the thermostat is set for cooling, the
reversing valve will be in the energized posion for cooling.
3.1 On a demand for cooling, the room thermostat energizes
“G” and “Y” and 24Vac is supplied to “Y” at the heat pump
and the “G” terminal on the EBTDR board.
3.2 The heat pump turned on in the cooling mode and aer a 7
second on delay, the relay on the EBTDR board is energized
and the blower motor starts.
3.3 When the cooling demand is sased, the room thermostat
removes the 24Vac from “G” and “Y”.
3.4 The heat pump is turned o and aer a 65 second delay o,
the relay on the EBTDR board is de-energized and the blower
motor is turned o.

On heat pump units, when the room thermostat 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. Some installaons may use one or more outdoor
thermostats to restrict the amount of electric heat that is
available above a preset ambient temperature. Use of oponal
controls such as these can change the operaon of the electric
heaters during the heang mode. This sequenceof operaon
does not cover those applicaons.
4.1 On a demand for rst stage heat with heat pump units, the
room thermostat energizes “G” and “Y” and 24Vac is sup-
plied to “Y” at the heat pump unit and the “G” terminal on
the EBTDR board. The heat pump is turned on in the heang
mode and the blower motor starts aer a 7 second on delay.
4.2 If the rst stage heat demand cannot be sased by the
heat pump, the temperature indoors will connue to drop.
The room thermostat will then energize terminal “W2’ for
second stage heat and 24Vac will be supplied to heat se-
quencer HR1 on the heater assembly.
4.3 HR1 contacts M1 and M2 will close 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 ele-
ment, HR1 will contain a second set of contacts, M3 and M4,
which will close and turn on heater element #2. The blower
motor is already on as a result of terminal “G” on the EBTDR
board being energized for the rst stage heat demand.
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. If the
second stage heat demand, “W2” cannot be sased by the heat
pump, the temperature indoors will connue to drop. The room
thermostat will then energize “W3” and 24Vac will be supplied
to HR2 on the heater assembly. When the “W3” demand is
sased, the room thermostat 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. On most digital/


“W2” and “W3” demands will be removed.
4.4 As the temperature indoors increase, it will reach a point
where the second stage heat demand, “W2”, is sased.
When this happens, the room thermostat will remove the
24Vac from the coil of HR1. The contacts on HR1 will open
between 30 to 70 seconds and turn o both heater ele-
ment(s). The heat pump remains on along with the blower
motor because the “Y” demand for rst stage heat will sll
be present.
4.5 When the rst stage heat demand “Y” is sased, the room
thermostat will remove the 24Vac from “G” and “Y”. The