Service manual

SERVICING
34
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.
5.0 Defrost Operation
On heat pump units, when the room thermostat is 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.
5.1 The heat pump will be on and operating in the heating
mode as described the Heating Operation in section 4.
5.2 The defrost control in the heat pump unit checks to see
if a defrost is needed every 30, 60 or 90 minutes of heat
pump operation depending on the selectable setting by
monitoring the state of the defrost thermostat attached 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 initiate a defrost
cycle.
5.4 When a defrost cycle is initiated, the contacts of the
HVDR relay on the defrost board open and turns off 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
continue to run in this mode until the defrost cycle is
completed.
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
programmed 10 minute override time the defrost thermo-
stat is still closed, the defrost board will automatically
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
contacts of the LVDR relay will open and turn off the
reversing valve and electric heater(s). The unit will now be
back in a normal heating mode with a heat pump demand
for heating as described in the Heating Operation in
section 4.
S-41 AEP* & MBE WITH SINGLE STATE CON-
DENSERS
AEP* & MBE ELECTRONIC BLOWER TIME DELAY RELAY
SEQUENCE OF OPERATION
This document covers the basic sequence of operation for a
typical application with a mercury bulb thermostat. When a
digital/electronic thermostat is used, the on/off staging of the
auxiliary heat will vary. Refer to the installation instructions
and wiring diagrams provided with the MBE for specific wiring
connections, dip switch settings and system configuration.
AEP* & MBE WITH SINGLE STAGE CONDENSERS
When used with a single stage condenser, dip switch #4 must
be set to the on position on the VSTB inside the MBE. 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 must remain
connected.
1.0 Cooling Operation
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 unit. The VSTB inside the MBE will turn on the
blower motor and the motor will ramp up to the speed
programmed in the motor based on the settings 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 satisfied, the room thermo-
stat removes the 24Vac from “G” and “Y”. The MBEand
AEP* remove the 24Vac from “Y’ at the condenser and the
compressor and condenser fan are turned off. The blower
motor will ramp down to a complete stop based on the
time and rate programmed in the motor.
2.0 Heating Operation
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 MBEand AEP* units. The VSTB will turn
on the blower motor and the motor will ramp up to the
speed programmed in the motor based on the settings 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
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.