AS3251C Asphalt Screed Caterpillar

Troubleshooting the Screed Heating System

Reference Testing and Adjusting, KENR3709, "Screed Troubleshooting" for the following statements:

• The asphalt mat is tearing because the screed plate is cold.

• The screed plate may be cold because the screed heating system is not functioning.

Probable root cause for the screed heating system that is not functioning properly

• The system is not turned ON.

• The selected temperature setting is too low for the type of asphalt mix.

• The circuit breakers have tripped.

• The temperature sensor has failed.

• The temperature sensor or the wiring for the heater element is not correctly connected to the wrong section.

Probable causes of tripped circuit breakers

• The wiring is damaged.

• The wiring is incorrectly connected to the wrong section.

• The electrical connectors are damaged.

• The elements and the electrical wiring are submerged in water or wet.

• The circuit breaker has failed.

• The element is shorted or grounded.

Note: The following conditions aid in determining the possible root cause for the tripped circuit breakers. The following conditions aid in determining when you should test the heater elements.

Condition: The screed heats during start-up, but the circuit breakers trip after reaching a set point (dry conditions).

The element may not be failed. A tripped breaker is most likely from feedback of current to the circuit breaker when the element is turned to the OFF position. This action is typically a GFCI trip. It is likely that only one of the two elements in the suspected section will cause the trip. Disconnect the heater elements one at a time in order to determine if the heater element is causing the circuit breaker to trip. The interim solution is using a lower heat setting. This condition isgenerally worse when high heat setting is used. Go to Medium heat or go to Low heat, when possible. If the circuit breakers still continue to trip on the low heat setting, test the elements, as described below. Review the wiring for shorts or for grounds. Also, review the wiring schematics for latest potential updates that are available.

Condition: The circuit breakers immediately trip after starting the screed heating system (dry conditions).

First inspect the circuit breaker. Move the circuit breakers into different locations in order to determine if the tripped condition will follow the circuit breaker. Check the wiring connection at the breaker. Remove the wires and reinstall the wires into the circuit breaker. Use low air pressure to clean the generator and the circuit breakers. Refer to Special Instruction, SEHS9124, "Cleaning and Drying of the Generator" which instructs proper cleaning of the generator on a regular basis. If the tripped condition does not follow the circuit breaker, then test the suspected element using the test in the section below. Review the wiring for shorts or for grounds. Also, review the wiring schematics for latest potential updates that are available.

Condition: The screed does not heat to operating temperature and the circuit breakers have tripped (wet conditions).

The root cause may be due to the circuit breaker, shorts in the wiring, grounds in the wiring, shorts in the elements, or grounds in the elements. Determine if the elements were under water or if the elements are wet. Visually inspect the wiring connections and the wiring in the elements. Determine if moisture has entered the connectors or the connections at the elements. Dry the system in order to determine if the circuit breaker continues to trip. Move the circuit breakers into different locations in order to determine if the tripped condition will follow the circuit breaker. If the tripped condition does not follow the circuit breaker, then test the suspected element using the test in the section below. Dry the screed heating system in order to test the suspect element by unplugging the suspect element. Operate the system until the suspected heater element is dry. Connect the harness to the element. If you continue to have a tripped circuit breaker, test the heater elements as described below. If the circuit breaker trips cease. Inspect the wiring to the connectors and the connectors to the heater elements for any moisture that may have entered the system. Reseal the electrical connectors to the heater elements if signs of moisture are present.

Procedure for Screeds with Single Four Pin Deutsch Connectors

Illustration 1	g01571225
(1) Connectors For the Outer heating Element (2) Connectors For the Inner heating Element (3) Outer Heating Element (4) Inner Heating Element

Each of the four sections of the screed plate is assembled with an inner electric heating element (4) and an outer electric heating element (3). The Cat Electric Screed Control will output a diagnostic flash code in order to alert the operator when one or more of the electrical components in the heating system malfunctions. When a heating element is suspected to be malfunctioning, the following procedure should be performed.

Reference: For more information on the diagnostic flash codes, refer to System Operation, "Electric Heat System" in this manual.

TEST THE RESISTANCE OF THE HEATING ELEMENT.

Table 1 lists the part numbers for the various heating elements and the expected electrical resistance values.

1. Turn the ignition switch to the OFF position. Ensure that the machine is secured in order to prevent any movement.

2. Allow the screed plates to cool down. The heating elements must be checked at ambient air temperature.

3. Remove the covers for the screed plate in order to allow access to the connectors for the electric heating element.

4. Unplug the machine harness connectors from the connectors for the heating element.

5. Use an ohmmeter in order to check the resistance of the element.

6. Observe the resistance value on the ohmmeter. Match the part number and the location of the element to the resistance range that is shown in Table 1.

7. Repeat the process for the other heating elements.

Expected Result: The resistance value of the electric heating element is in the correct resistance range that is listed in the table for the part number of the element.

NOT OK - The resistance value of the electric heating element is NOT in the correct resistance range that is listed in the table for the part number of the element.

Repair: Replace the heater element.

Stop.

OK - The resistance value of the electric heating element is in the correct resistance range that is listed in the table for the part number for the element. The heating element is OK.

Repair: There is a problem with either the voltage supply for the heating elements or there is a problem with the wiring harness or components between the generator and the heating elements.

Reference: Refer to Electrical System Schematic, KENR6660 for information on the components and the wiring harness that supplies voltage to the heating elements.

Note: It is highly unlikely that the CAT Electric Heat Control is causing the problem in the electric heating system. Investigate all other possible causes of a problem before checking the control. Call your Caterpillar dealer before attempting to replace the control.

Stop.

TEST FOR A SHORT TO THE GROUND FAULT ON THE HEATER ELEMENT FOR THE SCREED.

This test is intended to check for a short to the ground fault in the heater elements. A short to the ground fault in the heater element would result in tripping the circuit breaker. The circuit breaker for a ground fault is located at the generator.

Illustration 2	g01619052
(9) Metal case (10) Connector

Note: The heater element should be dry and clean before taking the following measurements.

Note: The measurements should be taken with the heater element at ambient temperature.

1. Disconnect the plugs from the heating element.

2. Set the 300-8648 Insulation Tester to 500 VDC in order to use the insulation tester as a megohmmeter.

3. Use the tester in order to check for a lack of continuity between the metal case of the heater element and the resistance coil inside the heating element.

   1. Place one probe of the insulation tester on metal case (9) of the heater element.

   2. Place one probe of the insulation tester on the pin of connector (10) for the heater element.

   3. The insulation tester should indicate an infinite reading. The insulation tester will indicate an infinite reading and any reading of more than 500 Megohms with a ">" symbol.

4. Replace the heating element if the reading on the insulation tester is less than 500 Megohms.