Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
05/2023 Rev.21
47
Resistance can be measured as shown above. Any deviation from above values could indicate a
defective compressor.
4.
High Voltage/Insulation Test:
Test internal leakage with a megoh meter. Attach one lead to the
compressor case on a bare metal tube and to each compressor terminal to test the motor windings.
A short circuit at high voltages indicates a motor defect. Do not do this test under vacuum.
5. On single phase models, check the capacitor by substitution.
5.4 Control Board Diagnosis
The PCB is equipped with an on board seven-segment display (see Section 2.3)
for configuring various settings and displaying faults. During normal operation
the display remains off unless the configuration menu is accessed or a fault has
occurred. Faults will be annunciated on the display as shown below:
Display
Displayed Faults
AS-F
Supply Air Sensor Fault (Sensor Disconnected Or Faulty) If Equipped
DB-F
Dry Bulb / Outdoor Sensor Fault (Sensor Disconnected Or Faulty) If Equipped
DS-F
Defrost Sensor Fault (Sensor Disconnected Or Faulty) Heat Pumps Only
ES-F
Enthalpy Sensor Fault (Sensor Disconnected Or Faulty) If Equipped
LP-1
Low Pressure Lockout Compressor Circuit 1
LP-2
Low Pressure Lockout Compressor Circuit 2
HP-1
High Pressure Lockout Compressor Circuit 1
HP-2
High Pressure Lockout Compressor Circuit 2
03
Low Voltage "Brownout" 16VAC or Less for 10 Minutes
5.5 Control Board Diagnosis (Alternate Construction)
The control board (see section 1.6a for a complete description of the control board) has a red diagnostic
LED which indicates the lockout fault. The control board will enter into and indicate lockout if either
of the fault conditions (LPS or HPS) occur twice.
The contactor must be closed before the first fault condition can be recognized by the control board.
The contactor will be closed 3 minutes after the unit is energized and only if cooling is required. The
first fault condition will open the contactor and shutdown the unit. The contactor on the unit that has
the fault condition must be closed before the second fault condition can be recognized by the control
board. The contactor on the unit with the fault condition will close after 3 minutes if the unit is still
calling for cooling and if the fault condition no longer exists. If you get a second fault condition, the
contactor will open and shutdown the unit. The “red” led will have one blink if the high pressure switch
has opened twice and will have two blinks if the low pressure switch has opened twice. The unit must
be in the cooling mode (compressor contactor Closed) before a fault condition can occur.
