Mercedes-Benz W201 heater blows cold or weakly
W201 heater blows cold even though the engine warms up: what is the fault?
The most common cause is a clogged heater core or its hoses, so hot coolant does not circulate. The blockage can be limescale. Another possibility is a faulty thermostat. If coolant circulates through the core but the heat is still weak, the fault may be in the core or the position of the flaps.
How do I clean the W201 heater core?
Disconnect the core's hoses and run hot water through it mixed with dish soap, descaler or vinegar. Citric acid has also been used to remove limescale. If flushing is not enough, the core is replaced.
The heat is on the wrong side or the control has no effect: what should I check?
The temperature is controlled by an air flap, which is operated by a cable and a plastic shaft coming from the rotary switch. Check the shaft connection and the cable attachment, since a detached or broken part leaves the flap in the wrong position. The flaps are reached by removing the centre section of the dashboard.
Is it normal for cold air to come from the centre vents of the dashboard?
Yes. The W201's centre vents take in fresh air, so no warm air comes out of them. Warm air comes from the other vents.