GSZH5 Service Manual
63
SYSTEM OPERATION
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.
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
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
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.
When the defrost cycle is terminated, the contacts
of the HVDR relay will close to start the outdoor fan and
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.
MBE Electronic Blower Time Delay Relay AEPF Air
Handler
SEQUENCE OF OPERATION
This document covers the basic sequence of operation for
a typical application with a mercury bulb thermostat. When
of the auxiliary heat will vary. Refer to the installation
instructions and wiring diagrams provided with the MBE/
And VSX Condensers
When used with a single stage GSX, SSX, ASX, and VSX
condensers, dip switch #4 must be set to the on position
on the VSTB inside the MBE/AEPF. 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/AEPF 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/AEPF unit. The VSTB inside the MBE/
AEPF 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.
thermostat removes the 24Vac from “G” and “Y”. The MBE/
AEPF removes the 24Vac from “Y’ at the condenser and
blower motor will ramp down to a complete stop based on
the time and rate programmed in the motor.
On a demand for heat, the room thermostat energizes
“W1” and 24Vac is supplied to terminal “E/W1” of the
VSTB inside the MBE/AEPF unit. 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.
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.