The Carrier CARB-compliant gensets (24 series) includes thermal safety switches attached to the Diesel Oxidation Catalyst (DOC). These two normally closed switches are wired in series between the ignition “RUN” switch (IGN4) and Fuse 1 (F1). In the event of the DOC surface temperature exceeding 260°C / 500°F, the switches will open and break the circuit to the Engine Control Unit (ECU), turning off the unit.

These switches are self-resetting (SRT) and will close when the temperature drops below 180°C / 356°F: 12-00954-00 or 232°C / 450°F: 12-00955-00.

If the unit is found not operating with the ignition in the run position it is recommended that the DOC circuit be tested prior to putting the unit back into service.

The DOC circuit be tested by ohming (with power off), between IGN4 and F1 in the control box.

If the DOC switches are found open, check DOC surface temperature using an infrared temperature tool. If the DOC surface temperature is below their SRT, check each switch to determine which has failed and replace using kit 76-01018-00.

If the temperature is at or above the SRT, investigate the air intake indicator. If the indicator is red (RG) or Yellow (UG), clean filter element housing and change the air filter.

NOTE: As the DOC switches are self-resetting, it is recommended to start and run the unit for a minimum of 20 minutes. If the unit runs with no red glow on the DOC housing, then the unit was left in run position for other causes (low oil pressure, high coolant temp, lack of fuel). If the DOC glows replace the DOC (UG kit 76-01016-00, RG kit 76-01017-00).