OEM Mercedes-Benz A/C and Heating Parts
Why is My Mercedes-Benz AC Only Blowing Cold Air on One Side?
Air conditioning in your Mercedes-Benz blowing cold on one side but hot on the other? We'll tell you how to diagnose the problem for most of the brand's cars, plus what to do to fix it in a specific case: for most models in the Mercedes-Benz M-Class.
The #1 Reason: a Bad Temperature Blend Door Actuator
AC problems like blowing warm or not blowing cool, you can usually chalk up to a faulty blend door actuator. (They call these temperature blend door actuators or vent mode door actuators, too). This is a common problem with cars from the 1990s and 2000s, actually -- for instance, the Mercedes-Benz CLK 350 of the late 2000s, and the Mercedes-Benz C-Class and E-Class (models like C 220, E 420, and E 430, from the late 1990s and early 2000s.
You can tell one's the issue pretty easily, too, one way or the other. Just plug an advanced scan tool into your ride's onboard diagnostic (OBD) system) and run an inspection. Whatever Mercedes-Benz model you drive, the scanner should be able to 1. tell you whether the blend door actuator is working right and 2. send a signal to it, to tell it to run. If that doesn't work, though, and you hear clicking, then, most likely, you'll have to replace the actuator.
Luckily, how to do that on the brand's cars is pretty straightforward.
How to Replace a Blend Door Actuator
Most blend door actuators, you can find on the driver's side of most Mercedes-Benz vehicles, above the gas pedal but above or to the side of the HVAC box, if not on the passenger side; it's usually screwed in, with a corresponding electrical connector.
To change it, all you have to do, most of the time, is take out the glove compartment, remove the actuator itself (taking out any bolts in the process), disconnect its wiring harness, push a new actuator into place, put the bolts back in, reconnect the wiring harness, test the new actuator (adjust temperature and watch to make sure it's running), and then put the glove box back in.
For instance, here's how to do it for most Mercedes-Benz M-Class SUVs. You'll need some prying and key tools. (Your owner's manual may have more specific info on what to do for the model you drive. Consult it beforehand.)
Example: Replace Blend Door Actuator in Mercedes-Benz M-Class
- Take out the A-pillar trim panels, both left and right.
- Take off the upper and lower covers on the steering column (there should be a few screws to loosen and take out.)
- Take the instrument cluster off.
- Using a pry tool, take out the center section of the instrument panel.
- Using the right-size keys, take the radio out.
- Take the glove box off.
- Use a pry tool to remove the defroster vent strip.
- Remove the #128 side panels.
You should be able to follow general blend door actuator replacement instructions from there. Again, though, check your owner's manual to be sure of what to do (or, by all means, ask the pros.)
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