Pinpoint Test K: Insufficient, Erratic or No Heat

Climate Control System

Pinpoint Tests

Pinpoint Test K: Insufficient, Erratic or No Heat

NOTE: Coolant temperature is critical for heater performance. Diesel engines warm up more slowly than gasoline engines, especially if idling or under light engine loads. Under these conditions, cab heat Is not at peak performance. The diesel electric heater option is designed to provide cab heat during this normal extended warm-up period.

Normal Operation

Under normal operation, coolant flows from the engine through the heater core and back to the engine. Proper coolant temperatures are critical for good heater performance.

This pinpoint test is intended to diagnose the following:
- Plugged or partially plugged heater core
- Low engine coolant level
- Temperature blend door actuator(s)
- Temperature blend door(s) binding or stuck
- Auxiliary Heater Control Module (AHCM)

PINPOINT TEST K: INSUFFICIENT, ERRATIC OR NO HEAT

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K1 CHECK FOR CORRECT ENGINE COOLANT LEVEL

- Ignition OFF.
- Check the engine coolant level when hot and cold.
- Is the engine coolant at the correct level (hot/cold) as indicated on the engine coolant recovery reservoir?

Yes
GO to K3.

No
GO to K2.

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K2 CHECK THE ENGINE COOLING SYSTEM FOR LEAKS

- Pressure test the cooling system for leaks. Refer to Engine Cooling Engine Cooling.
- Does the engine cooling system leak?

Yes
REPAIR the engine coolant leak. TEST the system for normal operation.

No
FILL and BLEED the cooling system. REFER to Engine Cooling Cooling System Draining, Filling and Bleeding. After filling and bleeding the cooling system, GO to K3.

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K3 CHECK FOR COOLANT FLOW TO THE HEATER CORE

- Run the engine until it reaches normal operating temperature. Select the FLOOR position on the control assembly. Set the temperature control to full warm and the blower to the lowest setting.
- Using a suitable temperature measuring device, check the heater core inlet hose to see if it is hot.
- Is the heater core inlet hose hot?

Yes
GO to K4.

No
REFER to Engine Cooling Testing and Inspection to check cooling system function.

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K4 CHECK FOR A PLUGGED OR RESTRICTED HEATER CORE

- Using a suitable temperature measuring device, measure the heater core outlet hose temperature.
- Is the heater core outlet hose temperature similar to the inlet hose temperature (within approximately 6-17°C [10-30°F])?

Yes
For vehicles not equipped with electric heater: GO to Pinpoint Test O. Pinpoint Test O: Temperature Control is Inoperative/Does Not Operate Correctly

For vehicles equipped with electric heater, make sure the electric heater is working correctly. REFER to Auxiliary Electric Heater in Description and Operation for a complete description of electric heater operation. If the electric heater is working correctly, GO to Pinpoint Test O Pinpoint Test O: Temperature Control is Inoperative/Does Not Operate Correctly. If the electric heater is not working correctly GO to Pinpoint Test S. Pinpoint Test S: The Electric Heater is Inoperative/Does Not Operate Correctly

No
INSTALL a new heater core. REFER to Climate Control Removal and Replacement. TEST the system for normal operation.

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