22
M
od
Pac II, 9/09-15
4.3 Compressor Troubleshooting
NOTE: It is important to rule out other component failures before condemning the compressor.
The following electrical tests will aid diagnosis:
1.
Start-Up Voltage
: Measure the voltage at the compressor terminals during start-up. The
voltage must exceed the minimum shown in Table 4, section 2.2, or compressor failure is
likely. A low voltage condition must be corrected.
2.
Running Amperage
: Connect a clamp-on type ammeter to the (common) lead to the com
-
pressor. Turn on the supply voltage and energize the unit. The compressor will initially draw
high amperage; it should soon drop to the RLA value or less. If the amperage stays high,
check the motor winding resistances.
NoTE:
Feel the top of the compressor to see if it has overheated. If it is hot, the internal
overload may be open. You may have to wait several hours for it to reset.
3.
Motor Winding Resistances:
Using a digital volt-ohm meter (VOM), measure the resistance
across the compressor windings as shown on the following page:
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 megohmeter. 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.
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
