Information On Checking Cooling Output And Tools Required

This Service Information only outlines the testing procedure. Perform the detailed test for this heating and A/C system function as described in Guided Fault Finding. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding"  function (for the Climatronic Control Module -J255-).

For vehicles with a manual climate control system ("Basic" A/C system version) and Start/Stop function, the Stop function is prevented (for example, in heating mode) depending on the setting on the regulators and buttons (Front A/C Display Control Head 2 -E775-, Front A/C Display Control Head 3 -E776-, Front A/C Display Control Head 4 -E777- and Fresh Air and Recirculating Air Mode Button -E781-). As soon as there is a request for heating, the engine is started. In cooling mode, the Climatronic Control Module -J255- does not limit the Stop function.

If there is no Humidity Sensor -G355- installed on vehicles with a manual climate control system ("Basic" A/C system version), a permissible stop time is currently calculated by characteristic curves that are influenced by the measured exterior temperature, the "recirculating air mode" function and operating condition of the windshield wipers. The calculated time must be greater than approximately 20 seconds so that the Stop function is permitted by the Climatronic Control Module -J255-. The stop time can be shortened at a lower exterior temperature, when the recirculating air mode is active and/or when it is raining to prevent the windshield and door windows from fogging up. If the calculated time for the Stop function is less than approximately 20 seconds, it is prevented.

For vehicles with an automatic climate control system ("Convenience" A/C system version) and Start/Stop function, the Stop function is prevented depending on the setting on the regulators and buttons (Front A/C Display Control Head 2 -E775-, Front A/C Display Control Head 3 -E776-, Front A/C Display Control Head 4 -E777- and Defrost Button -E782-). If, for example, "defrost" mode is selected, the Stop function is not possible or is canceled and the engine is started as soon as this mode is selected. The same also applies if the difference between the selected specified temperature and the measured actual temperature exceeds a certain value in heating and cooling mode. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding"  function.