SERVICING
39
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.
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.
For the 3
rd
and 4
th
heater elements to
operate on a second stage heat demand, the PJ4
jumper on the VSTB inside the MBE and AEP* 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
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 and the
blower motor will change to high speed. When the “W2”
demand is satisfied, 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
off and the blower motor will change to low speed.
On
most digital/electronic thermostats, “W2” will re-
main 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
thermostat will remove the 24Vac from “E/W1” and the
VSTB removes the 24Vac from HR1. The contacts on
HR1 will open between 30 to 70 seconds and turn off the
heater element(s) and the blower motor ramps down to a
complete stop.
AEP* & MBE WITH SINGLE STAGE HEAT PUMPS
When used with a single stage heat pump, 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 heat pump.
The orange jumper
wire from terminal “Y1” to terminal “O” on the VSTB
inside the MBE must be removed.
3.0 Cooling Operation
