Service Manual

SERVICING
105
1.2 The compressor and condenser fan are turned on and after
a 7 second on delay, the relay on the EBTDR board is
energized and the blower motor starts.
1.3 When the cooling demand “Y” is satisfied, the room thermo-
stat removes the 24Vac from “G” and “Y”.
1.4 The compressor and condenser fan are turned off and after
a 65 second delay off, the relay on the EBTDR board is de-
energized and the blower is turned off.
2.0 Heating Operation
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 seconds
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 time, 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 3
rd
and 4
th
heater elements if available. 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. When the “W2” demand is
satisfied, 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 off. 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 thermo-
stat will remove the 24Vac from HR1. Both set of contacts
on the relay opens within 30 to 70 seconds and turn off the
heater element(s) and the blower motor.
MBR/AR*F WITH SINGLE STAGE HEAT PUMPS
3.0 Cooling Operation
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 position 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 after 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 satisfied, the room thermostat
removes the 24Vac from “G” and “Y”.
3.4 The heat pump is turned off and after a 65 second delay off,
the relay on the EBTDR board is de-energized and the blower
motor is turned off.
4.0 Heating Operation
On heat pump units, when the room thermostat set to the heating
mode, the reversing valve is not energized. As long as the
thermostat is set for heating, the reversing valve will be in the
de-energized position for heating except during a defrost cycle.
Some installations may use one or more outdoor thermostats
to restrict the amount of electric heat that is available above a
preset ambient temperature. Use of optional controls such as
these can change the operation of the electric heaters during the
heating mode. This sequenceof operation does not cover those
applications.
4.1 On a demand for first 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 heating mode
and the blower motor starts after a 7 second on delay.
4.2 If the first stage heat demand cannot be satisfied by the heat
pump, the temperature indoors will continue to drop. The
room thermostat will then energize terminal “W2’ for sec-
ond stage heat and 24Vac will be supplied to heat sequencer
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 time,
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. The blower motor
is already on as a result of terminal “G” on the EBTDR board
being energized for the first 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 3
rd
and 4
th
heater elements if available. If the
second stage heat demand, “W2” cannot be satisfied by the heat
pump, the temperature indoors will continue 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
satisfied, 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 off. On most digital/
electronic thermostats, “W3” will remain energized until the
first stage heat demand “Y” is satisfied and then the “G”, “Y”,
“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 satisfied.
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 off both heater element(s).
The heat pump remains on along with the blower motor
because the “Y” demand for first stage heat will still be
present.
4.5 When the first stage heat demand “Y” is satisfied, the room
thermostat will remove the 24Vac from “G” and “Y”. The heat
pump is turned off and the blower motor turns off after a 65
second off delay.