23
Marvair GAA A/C w/Gas Heat I&O Manual
06/2023 Rev.5
the heating setpoint is satisfied, the Indoor motor continues to run based on the fan purge timer
setpoint (default 90 seconds) selected in setting 3 of the configuration menu of the control board.
When the system is operating in Heap Pump mode the electric heat is considered as supplemental
heat and will only be allowed under certain conditions due to additional features that may be
used. These features include the Outdoor Sensor and SCKT (safety circuit). See ODS and SCKT
for more details.
ODS - Outdoor Sensor (Heat-Pumps Only)
The outdoor sensor only responds to the temperature of the outside air. The sensor is a 10K
NTC sensor probe. The factory setting is 50°F. This setpoint can be adjusted in 1F increments
from 0F to 70F in the control board configuration menu setting 11.
If the optional Outdoor Sensor is used (Heat-pump systems only). The electric heat will not
operate upon a request for “W2” unless the outdoor temperature is below the setpoint for the
ODS setpoint. If the sensor is not connected or faulty the electric heat will be allowed to operate
anytime a request for W2 is present.
Note:
A request for Cooling and Electric Heat at the same time is not allowed and the control
board will not allow the electric heat to operate.
SCKT – Safety Circuit (Heat-Pumps Only)
The SCKT is a selectable menu option in the control board configuration menu setting 10. The
options for this feature are Y=Yes or N=No. When set to Y=Yes, control board will prevent the
compressor and electric heat from operating simultaneously. In this case the compressor will
shut off upon a request for “W2” (Electric Heat). The compressor will remain off as long as the
request for W2 is active. Once the request for W2 satisfies the compressor will be allowed to
operate. The default setting for SCKT is N=No, the electric heat and compressor will be allowed
simultaneous operation in the heat pump heating mode.
Note:
If the ODS is used the electric heat will not operate unless the outdoor temperature is
below the ODS setpoint.
EHDD – Electric Heat During Defrost (Heat-Pumps Only)
The EHDD is a selectable menu option in the control board configuration menu setting 9.
The options for this feature are Y=Yes or N=No. When set to Y=Yes, control board will force
the electric heat to operate during a defrost cycle unless SCKT is set to Y=Yes or the outdoor
temperature is not below ODS (if equipped) setpoint. The default setting for EHDD is Y=Yes.
Note:
SCKT takes priority over ODS and EHDD.
5.0 Dehumidification Operation AC / HP
5.1 Hot Gas Reheat (if equipped) –
When there is a request for “Dehumidification” (HUM-signal
via Digital input or Modbus), this will result in the control board energizing the Indoor Fan (IBR),
Compressor 1 (CC1), Compressor 2 (CC2), Reversing Valve (RV) “heat pumps only” and the
Reheat (RH) relay outputs on the board. This forces the system to operate in the full capacity
cooling mode while energizing the reheat solenoid valve to allow hot gas to be introduced into
the supply air stream of the system for dehumidification operation. The indoor fan motor will
operate at the “Dehum” speed setting on the board or via Modbus. The indoor fan remains on
continuously but the outdoor fan modulates based on liquid line temperature. The Fan Cycle
Control Sensor (Low Ambient Control Sensor) monitors the liquid line to maintain a 90F liquid
line temperature. When the liquid line temperature is below 80F the outdoor fan will shut off. A
liquid line temperature above 115F will force the outdoor fan to operate at the maximum speed
