Generac — Block Heater Test
Testing & diagnosis
From a Generac service manual covering: 4077, 4079, 4109, 4389, 4390, 4456, 4674, 4675. Check it applies to your exact model before use.
Applies to: Generac 4077, Generac 4079, Generac 4109, Generac 4389, Generac 4456
Before you start
- In multiple hairpin configurations, one hairpin can fail while the others remain functioning. Note the jumper position so they can be properly reassembled.
Procedure
- Disconnect the heater from the power source.
- For heaters with a thermostat, allow the coolant to cool below the thermostat range or remove the heater from the engine.
- Check for continuity with an ohmmeter between the element terminals inside the electrical box (remove all wires to avoid a false reading).
- If there is continuity through the element, check for continuity across the thermostat terminals (if applicable).
- If there is no continuity between the element or thermostat terminals the heater has failed; determine the cause of failure.
- If there is continuity through both the element and the thermostat, the heater is fine and the problem is improper installation, faulty wiring or an air pocket.
Tools required
- Phillips screwdriver (slip-joint pliers for explosion proof) Amazon
- Needle nose pliers or nut driver Amazon
- Ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Generac 4077 →, Generac 4079 →, Generac 4109 →, Generac 4389 →, Generac 4456 →
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.