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Marvair ComPac AVHDA I&O Manual 03/2019 Rev.3
3.
Motor Winding Resistances:
Using a digital volt-ohm meter (VOM), measure the resistance across
the compressor windings as shown below.
C
S
R
R
2
R
1
R
3
SINGLE
PHASE
R
3
> R
2
> R
1
R
3
= R
2
+ R
1
T
1
T
2
T
3
R
2
R
1
R
3
THREE
PHASE
R
3
= R
2
= R
1
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.
4.4 Control Board Diagnosis
The control board (see section 1.6 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 compressor 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 compressor 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.
