GSZH5 Service Manual
67
SYSTEM OPERATION
3.1 On a demand for cooling, the room thermostat
energizes “G” and “Y1” and 24Vac is supplied to “G” and
“Ylow/Y1” of the MBE unit. The VSTB inside the MBE will
turn on the blower motor and the motor will ramp up to
60% of 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 heat pump and the compressor and outdoor
fan starts in low speed operation.
room thermostat will energize “Y2” and supply 24Vac to
“Y/Y2”of the MBE unit. The blower motor will change to
the cfm for high speed operation and the VSTB will supply
24Vac to “Y2” at the heat pump. The compressor and
outdoor fan will change to high speed operation. When
the “Y2” demand and the VSTB will remove the 24Vac
from “Y2” at the heat pump. The blower will drop to 60%
of the programmed cfm and the compressor and outdoor
fan will change to low speed operation.
3.3
the room thermostat removes the 24Vac from “G” and “Y1”.
The VSTB removes the 24Vac from “Y’ at the heat pump
blower motor will ramp down to a complete stop based on
the time and rate programmed in the motor.
4.0 Heating 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. 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 sequence of operation does not cover those
applications.
4.1
the room thermostat energizes “G” and “Y1” and 24Vac is
supplied to “G” and “Ylo/Y1” of the MBE/AEPF. The VSTB
will turn on the blower motor and the motor will ramp up to
60% of the speed programmed in the motor based on the
settings of dip switch 1 and 2. The VSTB will supply 24Vac
to “Y” at the heat pump. The compressor will start on
low stage and outdoor fan will start on low speed on a
heating operation.
If a thermostat that provides a “Y2” demand in heating
the room thermostat will energize “Y2” and supply 24Vac
to “Y/Y2” of the MBE unit. The blower motor will change
to the cfm for high speed heating operation and the VSTB
will supply 24Vac to “Y/Y2” at the heat pump. The outdoor
fan will change to high speed operation and compressor
will shift to high stage. If the “Y2” demand is present and
demand and the VSTB will remove the 24Vac from “Y/
Y2” at the heat pump. The blower will drop to 60% of the
programmed cfm and the outdoor fan will change to low
speed. On most digital/electronic thermostats, “Y2” will
removed.
4.3 If the heat pump operation cannot satisfy the demand,
the room thermostat energizes “W2/W3” and 24Vac is
supplied to terminal “E/W1” of the VSTB inside the MBE/
AEPF unit. The VSTB will supply 24Vac to heat sequencer
HR1 on the electric heater assembly.
4.4 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, M3and M4,
which will close and turn on heater element #2.
If more than two heater elements are on
the heater assembly, it will contain a second heat
heater elements if available. For the 3rd and 4th
heater elements to operate on a second stage auxiliary
heat demand, the PJ4 jumper on the VSTB inside the
will continue to drop. The room thermostat will then
will be removed.