Preparation For Function Test

WARNING: This page is about a different car, the 1997 Mercedes-Benz C280 and 1997 Mercedes-Benz C230. However, it is still accessible from the selected car via links, so may be relevant.

Check fuses No. 4, 7 and 8. Check in-vehicle temperature sensor ventilation fan by placing a small piece of paper over fan vent grille with ignition on. Vent grille is located near dome light. See Figure. If sufficient ventilation is present, paper will remain on vent grille. If not, check ventilation fan voltage supply.
Put shift lever in "P" and engage parking brake. Run engine until it reaches normal operating temperature. Manually open center and side air outlets. Ensure recirculation button is not depressed.
To check defrost, put temperature at a random setting. Press defrost button. If operation is correct, fan speed will increase, air will vent from upper outlets, A/C compressor will be engaged, there will be maximum heat output, and inlet air will be 100 percent fresh air. If this mode does not operate properly, see:
To check total ventilation in cooling mode, set temperature to LO. Press AUTO button. If this mode is operating properly, fan speed will increase, air will vent from center and side outlets, A/C compressor will be engaged and there will no heat output. If this mode does not operate properly, see:
To check normal ventilation in regulating mode, put temperature at present in-vehicle temperature. Press AUTO button. If this mode is operating properly, fan speed will decrease, air will vent from upper outlets and leak from lower outlets, A/C compressor will be engaged, temperature of outlet air will be controlled, and duovalve and coolant pump will cycle. If this mode does not operate properly, see:
To check EC operation not in heating mode, set temperature to LO. Press EC button. Press dash air outlet mode. If this mode is operating properly, air will vent from dash outlets and A/C compressor will be off. If this mode does not operate properly, see:
- DTC 419: A/C COMPRESSOR ACTIVATION CIRCUIT
- DTC 451: DIVERTER VALVE
- VACUUM CIRCUITS & SWITCHOVER VALVES under TESTING.
To check economy in heating mode, set temperature to HI. Press EC button. If this mode is operating properly, air will vent from footwell and side outlets, leak from defroster outlets, and maximum heat will be output. If this mode does not operate properly, see:
To check REST mode, turn ignition off. Press REST. Set temperature to 79°F. If this mode is operating properly, heated air will vent from footwell and side outlets, leak from defroster outlets, and blower will operate at low speed. If this mode does not operate properly, see: