The centre air vents of the R129 (2000 SL320) have ceased to function.

[another_clean_sheet]

The cessation of airflow from the central air vents occurred some weeks ago, and the cause remains unknown to me. The air conditioning system works well, as does the heating system. The lateral ventilation outlets function adequately. When the red button on the vents is pressed, warm air is emitted from both the top and side vents. Conversely, pressing the blue button causes the top and side vents to release cold air. The symbols shown on the screen only indicate the direction of airflow towards the front and footwell areas, rather than the screen itself. However, despite this indication, air continues to be emitted from the screen vents. There seems to be a malfunction in the mechanism responsible for diverting airflow between the screen and central vents.
While the issue at hand is not of significant magnitude, I am curious whether there exist any expeditious and straightforward procedures that I might do to assess the situation. The diagnostics on the climate control panel were conducted, however, no fault codes were detected.

[xsports]

If I recall correctly, the first versions of the R129 had electrically controlled pneumatic flaps that were operated via vacuum diaphragms. Over time, these diaphragms tend to deteriorate and develop leaks, resulting in a failure to function properly. It is possible that subsequent models may have transitioned to a fully electronic system. I am uncertain about the matter at hand. One issue associated with electrically switched pneumatic valves is that despite the absence of fault codes, their operation may be hindered due to the presence of vacuum leaks.

[xsports]

[another_clean_sheet]

I express my gratitude for your assistance. I have familiarised myself with the hoover system. The complexity of these automobiles is notable, since they exhibited a high level of advancement relative to the era in which they were produced. It is presumed that the reference to the "passenger side UK" pertains to the positioning of the passenger side in vehicles driven in the United Kingdom.
I will examine the matter in the morning. Is it a straightforward process to experience being forcibly expelled and having an object get dislodged?

[xsports]

It is probable that the operator diaphragm has failed. To assess the vacuum integrity, one may use a handheld vacuum pump to locate the operational line. Addressing the issue of a potential leak in the operator itself may provide a distinct challenge.

[xsports]

This pertains to a course in the C programming language, where the fundamental ideas remain consistent.

[another_clean_sheet]

Thank you for your response. It seems that the subject matter is beyond my current understanding. It may be advisable to locate a reputable independent Mercedes-Benz garage in the county of Kent that has expertise in R129 models.

[xsports]

The primary issue at hand pertains to the accessibility and proficiency in handling outdated technology. It should be noted that not all individuals operating independently possess the necessary familiarity in this regard. Therefore, it is advisable to inquire about the particular number of repairs they have successfully conducted in relation to this technology. The expenses associated with labour may be elevated.
 

[another_clean_sheet]

I successfully identified and rectified the issue independently, at a cost of less than £3, by acquiring a replacement vacuum pipe connection.

[xsports]

I am pleased that the issue was resolved at a relatively low cost, at a location that is easily accessible and not deeply embedded inside the internal components of the heater/air conditioning system. Was the leakage seen on the air handler assembly or the 15-way switchover valve assembly?
 

[another_clean_sheet]

Upon raising the bonnet, it was seen that the location of interest was situated on the near side of the vehicle, namely in close proximity to the bonnet hinge, according to the standard configuration in the United Kingdom. A tiny connection module. Readily apparent and conveniently accessible. I had a sense of great satisfaction and perceived myself to be fortunate.

[another_clean_sheet]

[xsports]

The adage "a picture is worth a thousand words" might perhaps provide assistance to a fellow owner of an R129 vehicle in the future.

[Rudy7831]

Could you kindly provide the location of this issue, as I am experiencing a similar problem with the driver's side vent?

The user expresses gratitude.