Cummins/Onan — Heating System Performance Check
Testing & diagnosis
From a Cummins/Onan service manual covering: ES2075s, FS1870s, M11979s, M1976s, M1977s, M1978s. Check it applies to your exact model before use.
Applies to: Kubota 2482B engine
Procedure
- Put the Heat/Off/AC switch in the Heat position and set the Temp control to the hottest setting and Fan switch to High.
- Allow the power unit to operate for 5 more minutes.
- Measure the heat output from the sleeper duct with a thermometer.
- Verify the air outlet temperature is 120°F (49°C) or more.
- If no heat is produced, check the solenoid valve assembly and coolant level.
- If heat output is low, check for low coolant level or a restriction in the heater hoses.
Tools required
- thermometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Air outlet temperature: 120°F (49°C) or more
Source: Cummins/Onan 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.