8 TROUBLESHOOTING
Symptom Possible Cause Check or Remedy
Condenser will not
start
No power to condenser. Check voltage at input terminal block.
Circuit breaker or fuse for low-voltage
transformer in condenser is tripped.
Locate problem in condenser electrical panel and repair.
No low-voltage signal to/from indoor
unit.
Locate open circuit and repair.
Low discharge
pressure
Faulty head pressure control valve or
premium efficiency control board.
Replace if defective.
High discharge
pressure
Dirty condenser fins. Clean coil.
Condenser fans not operating.
Check for low-voltage signal from indoor unit.
Check fan motors and fuses.
High refrigerant charge Check refrigerant charge.
SPD green and red
LEDs are
extinguished
No voltage or improper phasing exists
at condenser.
Check voltage at input terminal block.
Electrical connections to SPD are
faulty.
Locate connection problem and repair.
Condenser disconnect is turned Off. Recheck lights with disconnect switch in the On position.
SPD red LED is
illuminated
A surge exceeding the rating of the
SPD has occurred.
Replace SPD and inspect other components for damage and replace them if
necessary.
Control Board LEDs
do not light.
Connection to P24 is loose or
disconnected.
Check the connection to P24 to verify that is connected securely.
Check the connector from the transformer for loose terminals.
Fuse located next to P24 has blown. Verify that the fuses next to P24 have not blown. Replace as needed.
24V transformer has failed.
With a voltmeter verify that the output from the transformer is 24Vac ±10%. If the
value exceeds ±10%, verify that the correct primary leads are being used.
Premium Efficiency Control Board has
failed.
If there is no output voltage, verify that the primary connections are secure and
receiving the correct voltage. If they are, replace the transformer.
Fan will not run
Jumper not installed between 24V and
DIN1 (for Ziehl-Abegg fan motor).
Install jumper between 24V and DIN1 (for Ziehl Abegg fan motor).
Table 8.1
Troubleshooting
Vertiv | Liebert® MC™ Installer/User Guide | 87
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