Pinpoint Test D: Insufficient, Erratic or No Heat

Climate Control System

Pinpoint Tests

Pinpoint Test D: Insufficient, Erratic or No Heat

Normal Operation

Under normal operation, the function selector switch receives engine vacuum. When OFF or MAX A/C is selected, vacuum is applied to the recirculation vacuum control motor. When the temperature is in the full COOL position, the heater control valve vacuum switch applies vacuum to the heater control valve.

This pinpoint test is intended to diagnose the following:
- Function selector switch
- Heater control valve
- Stuck or bound linkage or door
- Leaking or plugged vacuum hose
- Temperature blend door actuator



PINPOINT TEST D: INSUFFICIENT, ERRATIC OR NO HEAT

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D1 INSPECT FOR CORRECT ENGINE COOLANT LEVEL


- Ignition OFF.
- Inspect the engine coolant level when the engine is hot and when cold.




- Is the engine coolant at the correct levels?

Yes
GO to D3.

No
GO to D2.

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D2 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, including the radiator cap, hold pressure?

Yes
GO to D3.

No
REPAIR the engine cooling system leak. TEST the system for normal operation.

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D3 CHECK FOR HOT COOLANT AT THE HEATER CORE INLET HOSE


- Allow the engine to reach normal operating temperature.
- Place the function selector switch in the FLOOR position and the temperature control switch in the full WARM position.
- 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 D4.

No
GO to D5.

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D4 CHECK FOR HOT COOLANT AT THE HEATER CORE OUTLET HOSE


- 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
GO to Pinpoint Test H. Pinpoint Test H: Temperature Control is Inoperative/Does Not Operate Correctly

No
CARRY OUT the heater core component test. REFER to Heater Core under Component Tests to determine whether a plugged or partially plugged condition exists. Climate Control System

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D5 CHECK FOR HOT COOLANT AT THE HEATER CONTROL VALVE INLET HOSE


- Ignition OFF.
- Using a suitable temperature measuring device, check the heater control valve inlet hose.




- Is the heater control valve inlet hose hot?

Yes
GO to D6.

No
GO to Cooling System &/or Engine Block Heater to check the engine cooling system function.

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D6 CHECK FOR VACUUM TO THE HEATER CONTROL VALVE


- NOTICE: When disconnecting the heater control valve, position the vacuum line away from the cooling fan and the accessory drive system or vacuum line damage may occur.
- Disconnect the vacuum line from the heater control valve.




- Ignition ON.
- With the engine running, check for the presence of vacuum at the heater control valve vacuum line.
- Is vacuum present?

Yes
GO to D7.

No
INSTALL a new heater control valve. TEST the system for normal operation.

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D7 CHECK FOR INCORRECT VACUUM LINE PLACEMENT


- Ignition OFF.
- Inspect the heater control valve and A/C vacuum lines for correct placement.
- Is the vacuum line placement correct?

Yes
INSTALL a new climate control assembly. TEST the system for normal operation.

No
CORRECT the vacuum line placement. TEST the system for normal operation.

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