Generac — Testing the Genistor
Testing & diagnosis · Genistor (frequency converter)
From a Generac service manual covering: GN-190, GN-220, NP-30G, NP-40G. Check it applies to your exact model before use.
Applies to: Generac NP-30G, Generac GN-190 / GN-220 engine, Generac GN-220 engine
Before you start
- DO NOT attempt to test the Genistor until ALL leads have been disconnected. It MUST be completely disconnected from the circuit or all test results are invalid.
Procedure
- Disconnect all wires from the Genistor before testing.
- Set a VOM to a resistance scale allowing 20-60 ohms to be read and zero the meter.
- Connect one VOM lead to COM and the other to terminals G1, G2, G3 and G4 one at a time; each should read 20-60 ohms.
- Set the VOM to Rx1; connect across COM terminal and the center screw; should read continuity.
- Check continuity across each AC1, AC2, SL1 and SL2 screw to its terminal.
- Set VOM to Rx10,000 or Rx1K; there should be no continuity (infinity) between any of the screws.
- Replace the Genistor if it fails any of these tests.
Tools required
- VOM (volt-ohm-milliammeter) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- COM to G1/G2/G3/G4 = 20-60 ohms
Full service-parts list: Generac NP-30G →
Source: Generac service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.