FILTER AS-AIR 4886446 - Caterpillar

Varistor Test
External Varistor Test
The following procedure tests the normal state capability of the external varistor module that is used with half wave rectifier diode modules. If any meter reading does not fall within the given range, replace the heat sink assembly. Refer to the "Removal/Installation Instructions" section.
Remove all of the leads that are connected to the varistor module. Discard the star washers.
Place the megohmmeter test leads on the varistor module terminals. The varistor module is not polarity sensitive.
If the megohmmeter is not capable of reading DC voltages, then connect a DC voltmeter across the varistor module terminals.
Select the 1000 VDC range on the megohmmeter.
Apply 1000 VDC across the varistor module terminals. Note: Do not apply voltage for more than three (3) seconds.
The megohmeter should read between 735 VDC and 910 VDC.
If the reading is greater than 910 VDC, the varistor is "OPEN". The varistor has failed. Replace the heat sink assembly. Refer to the "Removal/Installation Instructions" section.
If the megohmeter reading is less than 735 VDC, then the varistor is "SHORTED" or "DEGRADED". The varistor has failed or is failing. Replace the heat sink assembly. Refer to the "Removal/Installation Instructions". Note: If the varistor module has