Pinpoint Test H: Insufficient, Erratic Or No Heat
Climate Control System
Pinpoint Tests
Pinpoint Test H: 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 will not be 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 heater core
- Coolant level
- Temperature blend door
PINPOINT TEST H: INSUFFICIENT, ERRATIC OR NO HEAT
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H1 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 H3.
No
GO to H2.
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H2 CHECK THE ENGINE COOLING SYSTEM FOR LEAKS
- Pressure test the cooling system for leaks. Refer to Cooling System &/or Engine Block Heater.
- 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 Cooling System &/or Engine Block Heater. After filling and bleeding the cooling system, GO to H3.
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H3 CHECK FOR COOLANT FLOW TO THE HEATER CORE
- Run the engine until it reaches normal operation 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 H4.
No
REFER to Cooling System &/or Engine Block Heater to check cooling system function.
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H4 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:
For EMTC systems, GO to Pinpoint Test L. Pinpoint Test L: Temperature Control is Inoperative/Does Not Operate Correctly - EMTC Systems, Vehicles Not Equipped With Elect
For DATC systems, GO to Pinpoint Test M. Pinpoint Test M: Temperature Control is Inoperative/Does Not Operate Correctly - DATC Systems, Vehicles Not Equipped With Elect
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, For EMTC systems, GO to Pinpoint Test N. Pinpoint Test N: Temperature Control is Inoperative/Does Not Operate Correctly - EMTC Systems, Vehicles Equipped With Electric
If the electric heater is working correctly, For DATC systems, GO to Pinpoint Test O. Pinpoint Test O: Temperature Control is Inoperative/Does Not Operate Correctly - DATC Systems, Vehicles Equipped With Electric
If the electric heater is not working correctly diagnose that first.
No
INSTALL a new heater core. TEST the system for normal operation.
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