W124 owner's heating & air-conditioning tips

[Greg]

This is an article I wrote for "Das Rundschreiben", the magazine of the Mercedes-Benz Club of NSW back in autumn of 2003. It explains the correct method of operation for the heating and air-conditioning in the W124 models, a system which is often misunderstood and used incorrectly. The same article also applies to some other models such as the W202 and W210 (although these do not have the actual temperatures marked on the temperature control thumbwheels). The article reads:


With winter approaching I considered it timely to discuss the climate control system in the W124 series sold in Australia from 1986 to 1995 in sedan, coupe, cabriolet and wagon body styles.

The W124 came with either a standard manual climate control system as was fitted to most Australian delivered vehicles or an optional automatic climate control system that was fitted to North American deliveries. The former system will be discussed here.
From my observations, the excellent climate control system in the W124 is often misunderstood and used incorrectly. The system I refer to has a central vertical row of three pushbuttons flanked on the left by a rotary air volume/fan speed control and on the right is a second rotary control which directs air to the windscreen, floor or dashboard vents or a combination of all. At the extreme left and right are thumbwheel controls with red, white and blue segments. Closer investigation will reveal these controls are also scaled in degrees Celsius. These controls allow the temperature for the driver's and passenger's side of the car to be individually set. It is these controls which are commonly misunderstood. Invariably they are either wound right up into the red or down into the blue. This effectively negates the temperature control forcing the system to either continually heat or cool. By setting these controls to a realistic temperature you will find that the system will maintain a comfortable temperature regardless of what the weather is doing outside. We find that with our 300TE we can leave these controls set to about 22 degrees year round (as recommended in the owner's manual) and rarely need to alter them. If the cabin gets colder than this the heater will operate. If it gets hotter the air conditioner will operate. Winding the controls to their extremes will not cause the system to reach a desired temperature any faster. It simply means you will be distracted from driving the car more often fiddling with the controls.

The air volume/fan speed control is self-explanatory. Only ever switch it completely off when travelling through dust. The directional control is also self-explanatory. The upper centre button allows the demist mode to be selected by running the air conditioner to de-humidify while the heater runs to maintain the set temperature. The centre button allows the air conditioner to run when required. In the early models illuminated is on. In the late models it is marked EC. When illuminated it is in economy mode, which disables the air conditioner. Obviously, with the air conditioner disabled the system can only heat up to the desired temperature, not cool from a higher temperature. With the temperature controls correctly set, it is feasible to leave the air conditioner enabled year round. It will only operate when required. The lower button selects recirculating air mode, which also should only ever be used for short periods.

In all, an excellent system that works superbly when used correctly.