SYSTEM OPERATION
62
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 third stage heat demand,
the PJ4 jumper on the VSTB inside the MBE/AEPF
must be cut. 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 “W/W2” of the MBE/AEPF. The VSTB will supply
24Vac to HR2 on the electric heater assembly. When
the “W3” demand is satisfied, the room thermostat will
remove the 24Vac from “W/W2” of the MBE/AEPF. 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 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 “E/W1” of the MBE/AEPF. 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/
Y2” of the MBE/AEPF. The VSTB removes the 24Vac from
“Y” at the heat pump and the heat pump is turned off. The
blower motor will ramp down to a complete stop based on
the time and rate programmed in the motor control.
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.
5.4a
For models with defrost control PCBDM133 or
PCBDM160, a 30 second compressor delay at defrost
initiation/termination is optional. As shipped from the
factory, the control is set for the delay (“DLY”), which will
turn the compressor off for 30 seconds while the reversing
valve shifts to/from the cooling mode position. To bypass
the delay, which typically reduces sound levels during
defrost mode, change the pin settings 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 programmed 10 minute override time the
defrost thermostat 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 on the defrost board 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. See section 5.4a.
MBE/AEPF With Two Stage ASX & DSX Condensers
1.0 Cooling Operation
When used with the ASX & DSX two stage condensers,
dip switch #4 must be set to the OFF position on the
VSTB inside the MBE/AEPF. The “Y1” output from
the indoor
thermostat must be connected to the purple
wire labeled “Ylow/Y1” inside the wire bundle marked
“Thermostat” and the purple wire labeled “Ylow/Y1” inside
the wire bundle marked “Outdoor Unit” must be connected
to “Ylow/Y1” at the condenser. The “Y2” 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/Y2” at
the condenser.
The orange jumper wire from terminal
“Y1” to terminal “O” on the VSTB inside the MBE/AEPF
must remain connected.
Summary of Contents for ANX
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