Information On Checking Heat Output And Tools Required
Special Tools And Workshop Equipment Required
- Vehicle Diagnostic Tester
- A standard thermometer (for temperature measurements, if necessary a thermometer with two measuring probes for simultaneous measurement, for example, for temperature on the right and left)
This Service Information only outlines the checking procedure. Perform the detailed function test for the heating as described in the Guided Fault Finding using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
If the coolant system is not bled completely after being filled, then air can get into the heater core for the heater. This will reduce the heating output and noises may result or the customer may complain there are different air temperatures coming out of the vents.
Corrective action for poor heating output or noises from coolant circuit:
- On vehicles without a high voltage system perform a test drive at high engine speed (at least 10 minutes, engine speed above 2500 RPM), while selecting a low gear to prevent excessive vehicle speed.
- If the customer complains of poor heating output at certain engine speeds, check the incorporation of the heater core for the heater in the engine coolant circuit. Refer to COOLING SYSTEM/COOLANT [CRUA, DEJA] / COOLANT SYSTEM/COOLANT [CNSB, CNTC] (Connection Diagram for Coolant Hoses).
- If the customer complains of poor heating output on a vehicle with a high voltage system, before performing the heat output test check the incorporation of the high voltage system in the coolant circuit as well as the activation and the function of the different shut-off valves, coolant pumps and the High Voltage Heater (PTC) -Z115-. Refer to HIGH VOLTAGE HEATER (PTC) -Z115-, INCORPORATION, IN THE COOLANT CIRCUIT , COOLING SYSTEM/COOLANT [CRUA, DEJA] / COOLANT SYSTEM/COOLANT [CNSB, CNTC] Connection Diagram for Coolant Hoses), Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the A/C system and the engine control module).
In vehicles without an A/C system with a Start-Stop System, the stop function is prevented depending on the setting on the Heater Control Module -J65- control head (for example, the heater is on). As soon as there is a request for heating, the engine is started.
In vehicles with a manually regulated A/C system and a Start-Stop System, the stop function is prevented depending on the setting on the A/C Control Module -J301- control head (for example, the heater is on). As soon as there is a request for heating, the engine is started. In cooling mode, the A/C Control Module -J301- does not limit the stop function.
If there is no Humidity Sensor -G355- installed on vehicles with a A/C Control Module -J301-, a permissible stop time is currently calculated by characteristics curves which are influenced by the measured outside air temperature, the "recirculated-air mode" function and operating status of the windshield wipers. The calculated time must be greater than 20 seconds so that the stop function is permitted by the A/C Control Module -J301-. The stop time can be shortened at a lower outside air temperature, when recirculated-air mode is active and/or when raining to prevent the front and door windows from fogging up. In the event the calculated time for the stop function is less than 20 seconds, this is prevented.
In vehicles with an Automatic climate control and a Start-Stop System, the stop function is prevented depending on the setting on the Climatronic Control Module -J255- control head. If, for example, "Defrost" is selected, the stop function is not possible or will be interrupted and the engine will start. The same applies in the case of heating and cooling. The difference between the target and actual temperature is greater than a specified value. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
On vehicles with a high voltage system depending on the different requirements of the coolant which flows through the heater core for the heater is warmed either from the engine or from the High Voltage Heater (PTC) -Z115-. Refer to HIGH VOLTAGE HEATER (PTC) -Z115-, INCORPORATION, IN THE COOLANT CIRCUIT , COOLING SYSTEM/COOLANT [CRUA, DEJA] / COOLANT SYSTEM/COOLANT [CNSB, CNTC] (Connection Diagram for Coolant Hoses). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the A/C system and the engine control module).
- Depending on the engine version, an After-Run Coolant Pump -V51- / Heater Support Pump -V488- may be installed (different designations, depending on the engine) in the coolant circuit to support the engine coolant pump on vehicles without a high voltage system. Refer to COOLING SYSTEM/COOLANT [CRUA, DEJA] / COOLANT SYSTEM/COOLANT [CNSB, CNTC] (Connection Diagram for Coolant Hoses) and the appropriate Wiring Diagram(s). The After-Run Coolant Pump -V51- / Heater Support Pump -V488- can be actuated in "stop mode" (engine stopped) to maintain the coolant flow rate through the heater core for the heater on with a cold engine or on vehicles with a Start/Stop System.
- Depending on the engine version on vehicles without a high voltage system, a Coolant Shut-Off Valve -N82- may be installed. Refer to COOLING SYSTEM/COOLANT [CRUA, DEJA] / COOLANT SYSTEM/COOLANT [CNSB, CNTC] / COOLANT VALVES, REMOVING AND INSTALLING (N82 & N488) (Connection Diagram for Coolant Hoses) and Wiring diagrams, Troubleshooting & Component locations. The Coolant Shut-Off Valve -N82- is then activated by the Engine Control Module -J623-, for example, when heating output is not requested by the Heater Control Module -J65- /A/C Control Module -J301- /Climatronic Control Module -J255- and the engine is still cold. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the engine control module). With an activated Coolant Shut-Off Valve -N82-, no warmed up coolant can flow the heater core for the heater.
- On vehicles with a high voltage system different shut-off valves, coolant pumps and a High Voltage Heater (PTC) -Z115- are installed in the refrigerant circuit. These components make sure that also in electric driving mode the vehicle interior (with the engine switched off) can be heated. Refer to HIGH VOLTAGE HEATER (PTC) -Z115-, INCORPORATION, IN THE COOLANT CIRCUIT .