Generac NP-30G / NP-40G — Testing the Genistor
Testing & diagnosis · Genistor (Frequency Converter)
For the Generac NP-30G / NP-40G, from the Generac service manual.
Applies to: Generac NP-30G, Generac GN-190 / GN-220 engine, Generac GN-190 or GN-220 (see NOTE 2) engine, Generac GN-220 engine
Before you start
- Do NOT test the Genistor until ALL leads have been disconnected. If testing is done with leads connected, all results are invalid.
Procedure
- Disconnect all wires from the Genistor.
- Set VOM to a scale reading about 20-60 ohms and zero the meter.
- Measure resistance from COM terminal to G1, G2, G3 and G4 one at a time (should be 20-60 ohms each).
- Set VOM to Rx1 and check continuity from COM to center screw.
- Check continuity from each screw to its matching terminal (AC1, AC2, SL1, SL2).
- Set VOM to Rx10,000 or Rx1K and verify no continuity (infinity) between any of the screws.
- Replace Genistor if it fails any test.
Tools required
- Volt-Ohm-Milliammeter (VOM) 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
- Between any two screws approximately 1 megohm
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.