The Thermo King Alarm 20 indicates that the diesel engine powering the CR steam engine did not start when requested by the microprocessor. The manufacturer provides the following description:

Alarm Code 20:

• Color Indicator: Yellow.
• Description: The engine (CR steam engine) did not start.
• Action: If the unit or area shuts down, repair it immediately. Otherwise, report the alarm at the end of the day.

Causes of Alarm 20:

The causes can be divided into two categories:

1. Mechanical Causes (Related to Fuel Supply):
   • Check for mechanical issues related to fuel supply to the diesel engine.
2. Electrical Causes (Related to Ignition and Fuel Supply Control):
   • Check for issues preventing ignition or affecting the control of fuel supply.

Mechanical Issues with Thermo King Alarm 20:

The normal operation of the fuel system is as follows:

• The electric fuel pump (5) creates a vacuum in the supply line in the fuel tank.
• Atmospheric pressure in the tank pushes fuel upward (line 6).
• Fuel reaches the fuel filter and part travels to the mechanical injection pump (9).
• Fuel is distributed according to the engine sequence to the pistons through the injectors (10).

What to Check with Alarm 20:

If you’re experiencing Alarm 20, it’s likely a fuel system issue. Check the fuel solenoid located at the back of the injection pump.

1. Fuel Solenoid Issues:
   • Clear alarms.
   • Stand in front of the unit and touch the side or back of the fuel solenoid.
   • Turn on the unit, keeping a finger on the solenoid. The unit should make a starting sound.
   • If the solenoid makes a sound, it’s energized and functioning correctly.
2. Blocked Fuel System:
   • Inspect the in-line fuel filter located at the inlet hose fitting of the transfer pump.
   • Remove the bolt and washers.
   • Take out the filter from inside the bolt and check for any clogs.
   • Clean the bolt, screen, and fitting.
   • Reinstall the bolt and washers. Replace the screw-on fuel filter if necessary.
3. Air Presence in the Fuel System:
   • Loosen the manual primer on the transfer pump.
   • Ensure the fuel tank has at least three-quarters of fuel; otherwise, add fuel.
   • Locate the vent fitting on top of the tank near the fuel supply and return lines.
   • Pressurize the fuel tank.
   • Bleed air from the fuel lines.
   • Open the purge bolt on top of the injection pump to release air. If needed, continue pressurizing and priming to remove all air.
4. Confirming Fuel Return:
   • Locate the return fuel line.
   • Loosen the hose connection and gently pull the line to check for fuel.
   • Lack of fuel indicates an air issue; constant, steady flow confirms a functioning fuel system.

Electrical Issues with Alarm 20:

The starter motor provides the initial impulse to the diesel engine for the first revolutions. Key components include:

• Starter motor.
• Starter solenoid.
• Pinion coupling.

The starter only works during startup, engaging through the coupling solenoid. Once the diesel engine starts turning on its own, the solenoid separates the coupling pinion, disconnecting the starter from the diesel engine.

What to Check for Electrical Issues:

1. Battery Voltage:
   • Test the battery voltage to ensure it supplies sufficient voltage to the starter motor.
2. Loose Connections:
   • Check for loose connections that may hinder sufficient current flow to the starter motor.
3. Starter Solenoid Operation:
   • Visually check the starter solenoid for proper operation. You can observe the coupling to the diesel engine or listen for the characteristic sound.
4. Diesel Engine Rotation:
   • Ensure the diesel engine rotates enough when using electric start.
5. Starter Motor Engagement:
   • If the starter engages but doesn’t turn, the issue may lie with the starter motor.