Heating Performance, Checking
Heating Performance, Checking
• If coolant circuit is not completely bled after filling, air may accumulate in heater core, thus reducing heating performance, additional noises may occur or customer may complain of different air temperatures flowing out of vents at driver side and front passenger side.
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 performance at specific engine speeds, check incorporation of 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.
- In vehicles with a parking/auxiliary heater, make sure the recirculation pump (V55) on the parking heater is working correctly and that the parking heater is incorporated side the coolant circuit
Requirements For Reaching Maximum Heating Performance
• The coolant circuit is bled in stages.
• All air ducts, covers and seals OK and properly installed.
• Check that the air flow through the dust and pollen filter is not obstructed by dirt. Refer to => [ Dust and Pollen Filter ] Service and Repair.
• Engine is warm.
• The Bowden cable and the release cable on the temperature flaps are OK.
• The engine thermostat is OK.
• The foam seal on the heater core is OK. Refer to => [ Installing ] Service and Repair.
• The functionality of the auxiliary air heater heating element (Z35) for diesel vehicles and the activation of the heater control module (J65) is OK. Refer to Vehicle Diagnosis, Testing and Information System in "Guided Fault Finding". (perform Guided Fault Finding on the auxiliary air heater).
• That the activation of the engine control module from the heater control module (J65) is OK for vehicles with a gasoline engine.
Test Prerequisites
• The coolant circuit is bled in stages.
• All air ducts, covers and seals OK and properly installed.
• Air flow through dust and pollen filter not obstructed by dirt.
• Engine is warm.
• Vehicle not exposed to sunlight.
Heating Performance, 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.
- 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.
• The heater works in fresh air mode, the indicator light for the recirculation -button does not light up.
• Fresh Air Blower runs at maximum speed.
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° 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.
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° 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.
Target 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 when bleeding the coolant circuit, and if necessary, replace.
- Check the connection for the heater core in the coolant circuit.
- Check the temperature adjustment and the temperature door operating cable. Refer to item 19 => [ (Item 19) Bowden Cable For Temperature Door ] Heater Overview.
- Check the foam seal on the heater core, refer to => [ Installing ] Service and Repair.
- Check the functionality of the temperature door in the air distribution housing. Refer to => [ Heating and A/C Unit ] Heating and A/C Unit.
- Check coolant thermostat (if the thermostat is faulty, the engine coolant temperature may not be warm enough).
• 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 19 => [ (Item 19) Bowden Cable For Temperature Door ] Heater Overview.
- Check the functionality of the temperature door in the air distribution housing. Refer to => [ Heating and A/C Unit ] Heating and A/C Unit.
- Check the plenum chamber and seal between engine compartment and plenum chamber.