Heating Output, Checking

Corrective action for poor heating output or noises from coolant circuit

-- Perform a lengthy test drive at high engine speed (at least 10 minutes, engine speed above 2500 RPM). Select a low gear during the test to prevent excessive vehicle speed.

-- If customer complains of poor heating output at certain engine speeds, check the integration of the heater core for the heater into 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 DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING or DIAGNOSIS AND TESTING .

-- In vehicles with a parking/auxiliary heater, check the activation of the Recirculation Pump -V55- on the parking heater and make sure that the parking heater is incorporated inside the coolant circuit.

Requirements for reaching maximum heating performance

• The coolant circuit is bled in stages. Refer to GENERAL INFORMATION , GENERAL INFORMATION , GENERAL INFORMATION , GENERAL INFORMATION or GENERAL INFORMATION .
• 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 .
• The engine is warm.
• The release cable and the operating lever on the temperature flaps are OK.
• The engine thermostat is OK. Refer to DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING or DIAGNOSIS AND TESTING .
• The foam seal on the heater core is OK. Refer to HEATER CORE .
• On vehicles with a Diesel engine, the function of the Auxiliary Heater Heating Element -Z35- and the activation of the Heater Control Module -J65- is OK. Perform "Guided Fault Finding" using the Vehicle Diagnostic Tester (on the auxiliary air heater) in Parking Heater (checking the auxiliary heater).
• On vehicles with a gasoline engine, the activation of the engine control module from the Heater Control Module -J65- is OK.

Test Prerequisites

• The coolant circuit is bled in stages. Refer to GENERAL INFORMATION , GENERAL INFORMATION , GENERAL INFORMATION , GENERAL INFORMATION or GENERAL INFORMATION .
• 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.

Heating Output, Checking

-- Close the engine hood.

-- Close doors, window and sunroof.

-- Open all instrument panel vents.

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

-- Start the engine.

-- Put the temperature dial to the stop "cold".

-- Put the air distribution dial on "instrument panel vent".

-- Set the fresh air blower dial to speed "4 ".

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

Target 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).

-- Set to the highest temperature possible (temperature dial in the stop "warm").

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

Target 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).

-- Set to the lowest temperature possible (temperature dial in the stop "cold").

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

Target 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 target values are not reached, check the following

• If the required heating output is not reached:

-- Check the bleeding for the coolant circuit and if necessary, repeat. Refer to GENERAL INFORMATION or GENERAL INFORMATION .

-- Check the incorporation of the heater core for the heater into the coolant circuit. Refer to DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING or DIAGNOSIS AND TESTING .

-- Check the release cable for setting the temperature and the operation of the temperature doors. See -item 19- in Figure.

-- Check the foam seal on the heater core for the heater. Refer to HEATER CORE .

-- Check the functionality of the temperature doors in the air distribution housing. Refer to HEATER AND A/C UNIT .

-- Check the coolant thermostat. The coolant may not heat properly if the coolant thermostat is malfunctioning. Refer to DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING , DIAGNOSIS AND TESTING or DIAGNOSIS AND TESTING .

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

-- Check the release cable for setting the temperature and the operation of the temperature doors -item 19- in Figure.

-- Check the functionality of the temperature doors in the air distribution housing. Refer to HEATER AND A/C UNIT .

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