Heat Output, Checking
Heat Output, Checking
Special tools, testers and auxiliary items required
• Vehicle Diagnosis, Testing And Information System (VAS 5051/) or
• Vehicle Diagnosis And Service System (VAS 5052)
• Diagnostic Cable - 3 Meter (VAS 5051/5A)
• If the coolant circuit is not completely bled after filling, air may accumulate in the heater core, reducing heating performance. Additional noises may occur or the customer may report different air temperatures coming out of the driver and passenger side vents.
Corrective action:
- Adjust the temperature knob on the Climatronic Control Module (J255) to the Warm setting (so the heat regulating valves are not closed).
- Adjust the blower speed knob on the Climatronic control module to a low fresh air blower speed (so the passenger compartment is not heated too much during the road test).
- 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 the customer reports poor heat output at certain engine speeds, check the connection in the coolant circuit for the Left Heat Regulating Valve (N175) and Right Heat Regulating Valve (N176) and the Coolant Pump (V50). If both coolant hoses (supply and return) from the engine or the electrical connections in the connector to the heat regulating valves and or the coolant pump are switched, the engine coolant pump works against the coolant pump and the heat regulating valves. Coolant no longer flows into the heat exchanger at certain engine speeds.
This test checks the function of the left heat regulating valve, the right heat regulating valve and the coolant pump.
• If the determined temperatures lie below the specification (heating performance too low):
- Check the function of the left heat regulating valve, the right heat regulating valve and the coolant pump using Vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.
If no malfunctions are detected:
- Check the coolant hoses (from the engine to the coolant pump and from the heater core back to the engine) to see if they are switched or constricted.
- Check the coolant pump contacts for interchange. Due to direction of pump operation.
- Check the left heat regulating valve and right heat regulating valve electrical terminals to see if they are switched and if they are connected correctly in the coolant circuit.
Test Prerequisites
• The coolant circuit has been bled properly.
• All air ducts, covers and seal OK and properly installed.
• The air flow through the dust and pollen filter is not affected by dirt in the filter. Refer to => [ Dust and Pollen Filter ] Service and Repair.
• The vehicle is not exposed to sunlight.
• The engine is warm.
• The Climatronic control module DTC memory has been checked and erased and basic setting has been performed using Vehicle Diagnosis, Testing and Information System VAS 5051/ under "Guided Fault Finding".
• The Climatronic control module code and adaptation have been checked. Refer to Vehicle diagnosis, testing and information system VAS 5051 under "Guided Fault Finding" function.
Checking
- Close the engine hood, the doors and the windows.
- Open all dash panel vents.
- Start the engine and adjust the following settings on the Climatronic control module:
• The temperature knob is in the cold position.
• A/C compressor on (the indicator lamp in the AC button comes on).
- Let the A/C system runs for several minutes at maximum cooling output (with the engine running).
- Switch off ignition.
- With the ignition switched off, connect the (VAS 5051/) with the (VAS 5051/5A) to the 16-pin Data Link Connector (DLC). Refer to Vehicle diagnosis, testing and information system VAS 5051 under "Guided Fault Finding" function.
- Switch ignition on.
- Initiate a Guided Fault Finding on the A/C system using Vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.
- Select the display group with the following values in "read measured values block". Left heat regulating valve, right heat regulating valve, A/C Compressor Regulator Valve (N280) and coolant pump activation. Check the measured values from the Left Vent Temperature Sensor (G150) and the Right Vent Temperature Sensor (G151) and check the display in the measured values block using Vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.
- Adjust the intermediate blower speed knob (Climatronic control module).
• The Climatronic control module starts working, the left heat regulating valve and right heat regulating valve are activated and closed.
• The Fresh Air Blower (V2) runs at an intermediate speed (activation at approximately 7V).
• Depending on the engine temperature, the coolant pump may be switched on due to a request from the engine control module even when it is not necessary based on the setting on the Climatronic control module.
• The heater core and the coolant lines to the heater core in the A/C unit are at the approximate ambient temperature or reach it after a certain time.
• The temperature of the air coming out of the heater heat exchanger is displayed in the measured values from the left vent temperature sensor and the right vent temperature sensor. Refer to Vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• If the Climatronic control module has been removed from the center console. The electrical connections cannot be separated for this purpose. If the coolant and refrigerant lines can be reached through the installation compartment, and their temperature can be felt with the hand (Climatronic control module removing, refer to => [ Climatronic Control Module ] Climatronic Control Module). To feel if the coolant lines are cooling off, carefully touch them through the installation shaft in the instrument panel (they may still be hot).
- Read the measure value of the battery state of charge. There may be no shut-offs due to low voltage from the Vehicle Electrical System Control Module (J519). Refer to Vehicle diagnosis, testing and information system VAS 5051 under "Guided Fault Finding" function.
• If the battery charge is too low, connect the Battery Charger (VAS 5900) to the vehicle.
- Read the left vent temperature sensor and the right vent temperature sensor using Vehicle diagnosis, testing and information system VAS 5051 under "Guided Fault Finding" function.
Specification:
• Ambient temperature plus maximum 15 °C
- Set the temperature rotary knob on the Climatronic control module to warm.
- Compare the measured values of left vent temperature sensor and right vent temperature sensor to each other.
Specified Values
• The temperature of the air coming from the heater core increases and reaches a value greater than 50° C (depending on the current engine temperature).
• The coolant pump runs.
• The fresh air blower runs at an intermediate speed (activation at approximately 7V).
• The left heat regulating valve and the right heat regulating valve are open and the coolant lines to the heater core in the A/C unit warm up.
• If the Climatronic control module has been removed from the center console. The electrical connections cannot be separated for this purpose. If the coolant and refrigerant lines can be reached through the installation compartment, and their temperature can be felt with the hand (Climatronic control module removing, refer to => [ Climatronic Control Module ] Climatronic Control Module). To feel if the coolant lines are warming up, carefully touch them through the installation shaft in the instrument panel (they may still be hot).
- Set the temperature rotary knob on the Climatronic control module to cold again.
- Compare the measured values from left vent temperature sensor and right vent temperature sensor with each other using the Vehicle diagnosis, testing and information system VAS 5051 under "Guided Fault Finding" function.
Specified Values
• The temperature decreases to the ambient temperature (plus a maximum of 15° C) within 5 minutes and the coolant lines to the heater core cool down.
• The left heat regulating valve and the right heat regulating valve are activated and closed.
If the specified values are not reached, check the following:
• Coolant circuit bleeding.
• Connection of the heater core in the coolant circuit.
• Activation and function of the left and right heat regulating valves, refer to => [ Left and Right Heat Regulating Valves ] Service and Repair and Vehicle diagnosis, testing and information system VAS 5051 under "Guided Fault Finding" function.
If the specified values are not reached and there is still a complaint, check the following:
• Foam seal on the A/C heater heat exchanger (if the seal is not installed correctly, air will flow over the heat exchanger and will be colder than specified in certain areas), refer to => [ ] A/C Unit Heat Exchanger.
• The engine coolant thermostat (if the thermostat is faulty, the engine coolant may not get warm enough).