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 coolant hoses (supply and return) of engine are interchanged, coolant is flowing in the wrong direction through the heater core. Refer to [FOR ENGINE(S) CPPA, CPRA, CPKA, CPLA] COOLING SYSTEM .

-- 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 is bled according to the guidelines. Refer to COOLANT, DRAINING AND FILLING .
• All air ducts, covers and seals 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 the appropriate service information .
• 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. Refer to Vehicle Diagnostic Tester in Guided Fault Finding  (perform Guided Fault Finding for the auxiliary heater) and refer to the appropriate service information (auxiliary heater test).
• That the activation of the engine control module from the Heater Control Module -J65- is OK for vehicles with a gasoline engine.

Test Requirements

• The coolant circuit is bled according to the guidelines. Refer to COOLANT, DRAINING AND FILLING .
• All air ducts, covers and seals OK and properly installed.
• Air flow through dust and pollen filter not obstructed by dirt.
• 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.

-- Position the temperature dial in the selection "cold".

-- Position the knob for air distribution on "instrument panel vent".

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

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

Specified Values: 

• The temperature of the air coming out of the left and right vents in the instrument panel is maximum 15 °C (59 °F) greater than in 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 (46.4 °F).

-- Adjust to the highest temperature possible (until temperature dial stops in "warm").

-- Measure temperature of the air flowing out of 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 (46.4 °F).

-- Adjust to the lowest temperature possible (until temperature dial stops in "cold").

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

Specified Values: 

• The temperature drops within 5 minutes to a value, which is maximum 15 °C (59 °F) greater than the previously measured ambient temperature

If the Values are not Reached, Check the Following

• If the required heat output is not reached:

-- Check the coolant circuit bleeding and repeat if necessary. Refer to COOLANT, DRAINING AND FILLING .

-- Check the incorporation of the heater core for the heater in the coolant circuit. Refer to CONNECTION DIAGRAM - COOLANT HOSES .

-- Check the temperature adjustment release cable or the operation of the temperature control doors. Refer to FLEXIBLE SHAFTS, REMOVING AND INSTALLING .

-- Check the foam seal on the heater core 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 COOLANT PUMP/THERMOSTAT .

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

-- Check the temperature adjustment release cable or the operation of the temperature control doors. Refer to FLEXIBLE SHAFTS, 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 plenum chamber and seal between engine compartment and plenum chamber.