Heating Output, Checking

Corrective Measure for Poor Heating Output or Noises from Coolant Circuit

-- Perform a longer test drive at higher engine speeds (at least 10 minutes, engine speed above 2500 rpm). Select a lower gear during the test to prevent excessive vehicle speed.

-- If the customer complains of poor heating output at certain engine speeds, check the integration of the heater core in the coolant circuit. If both engine coolant hoses (supply and return) are interchanged, then coolant is flowing in the wrong direction through the heater core. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .

-- For vehicles with a parking/auxiliary heater, check the activation of the Recirculation Pump -V55- for the parking heater as well as the incorporation of the parking heater in the coolant circuit.

Requirements for Reaching Maximum Heating Output

• The coolant circuit must be bled according to the guidelines. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .
• All air ducts, covers and seals are OK and properly installed.
• Check that the air flow through dust and pollen filter is not obstructed by dirt. Refer to DUST AND POLLEN FILTER, REMOVING AND INSTALLING .
• The engine is warm.
• The release cable and the release lever for the temperature doors are OK.
• The engine coolant thermostat is OK. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .
• The foam seal on the heater core is OK. Refer to HEATER CORE, REMOVING AND INSTALLING .
• For vehicles with a diesel engine, the function of the Auxiliary Heater Heating Element -Z35- and the activation of the Heater Control Module -J65- are OK. Use the Vehicle Diagnostic Tester in Guided Fault Finding  (perform Guided Fault Finding for the auxiliary heater).
• For vehicles with a gasoline engine, the activation of the engine control module from the Heater Control Module -J65- is OK.

Test Requirements

• The coolant circuit must be bled according to the guidelines. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .
• All air ducts, covers and seals are OK and properly installed.
• Air flow through dust and pollen filter not obstructed by contamination.
• The engine is warm.
• The vehicle is not exposed to sunlight.

Checking

-- Close the engine hood.

-- Close doors, window and sliding sunroof.

-- Open all instrument panel vents.

-- Measure the ambient temperature (temperature in the workshop).

-- Start the engine.

-- Set the temperature knob all the way to "cold".

-- Set the air distribution control knob to "instrument panel vent".

-- Adjust rotary fresh-air blower control to speed "4".

-- Measure the temperature of the air flowing out of the left and right instrument panel vents using a thermometer.

Specified Values:

• The temperature of the air coming out of the left and right instrument panel vents is maximum 15 °C (59 °F) greater than the previously measured ambient temperature.
• The temperature difference between the air coming out of the left and right instrument panel vents is less than 8 °C (46 °F).

-- Adjust to the highest temperature possible (temperature knob all the way to "warm"),

-- Measure the temperature of the air flowing out of the left and right instrument panel vents using a thermometer.

Specified Values:

• The temperature of the air coming out of the left and right instrument panel vents increases to a value greater than 55 °C (131 °F) (at a coolant temperature of approximately 90 °C (194 °F), depending on the current coolant temperature).
• The temperature difference between the air coming out of the left and right instrument panel vents is less than 8 °C (46 °F).

-- Set the lowest temperature possible (temperature knob at "cold" stop).

-- Measure the temperature of the air flowing out of the left and right instrument panel vents using a thermometer.

Specified Values:

• The temperature drops within five minutes to a value, which is maximum 15 °C (59 °F) greater than the previously measured ambient temperature

If the specified values are not reached, check the following:

• If the required heating output is not reached:

-- Check the coolant circuit bleeding and repeat, if necessary. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .

-- Check the incorporation of the heater core for the heater in the coolant circuit. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .

-- Check the temperature adjustment and the temperature door operating cable. Refer to Overview - Heater and A/C Unit, Left Side Door Control - List Item: Temperature Control Door Motor .

-- Check the foam seal on the heater core for the heater. Refer to HEATER CORE, REMOVING AND INSTALLING .

-- Check the functionality of the temperature door in the air distribution housing. Refer to HEATER AND A/C UNIT, DISASSEMBLING AND ASSEMBLING .

-- Check the coolant thermostat. The engine coolant may not heat properly if the coolant thermostat is faulty. Refer to [For engine(s) DGXA, DJXA] Cooling System/Coolant or [For engine(s) DKFA] Cooling System/Coolant .

• If the air coming out of the vents is too warm when it is set to "Cold".

-- Check the temperature adjustment and the temperature door operating cable. Refer to -item 6- Overview - Heater and A/C Unit, Left Side Door Control - List Item: Temperature Control Door Motor .

-- Check the functionality of the temperature door in the air distribution housing. Refer to HEATER AND A/C UNIT, DISASSEMBLING AND ASSEMBLING .

-- Check the plenum chamber and seal between engine compartment and plenum chamber