My first winter with this car and some questions come up.

1. When I set the temp for a warmer interior temp than the outside temp and hit auto mode, the Air Conditioner still is activated. Regardless out outside humidity.
Shouldn't the unit manually shut off the AC compressor in cold weather? Why is it a manual function and if it does run all the time, will this not wear it out sooner?
2. It seems that the first 10-15 minutes or so, the unit still blows cold air regardless of the engine temp. This is all vents, not just the center two.

What am I missing here?

TIA

 

The AC acts as a dehumidifier to help with clearing the moisture of the inside of the windows.

 

Are you talking about a 2005 E320CDI?

On any car the A/C compressor would work down to an ambient temperature of about 5 (4-7) degrees Celsius. At a lower temperature there wold be a risk of the evaporator getting frozen (which is why the evaporator anyway does not go below some +4 degrees Celsius).

The compressor would not need to work as hard as at summer because it would not need to reduce the air temperature equally much.

The point of the A/C working also when the set interior temperature is higher than the outside temperature is that often humidity needs to be reduced from the air entering the cabin. Only when the car is warming up the air significantly, would this threat disappear.

Not sure about your car but my W221 has a humidity sensor and at winter conditions it would only reduce incoming air temperature enough to get the humidity low enough. Not all cars have this sensor and then, as they are not aware of the necessary humidity reduction, those simply always work to reduce the incoming air to (about) 4 degrees and then warm it up to the set temperature. Actually MB documentation says that the humidity sensor operation is disabled from W221 cars for certain markets, like the USA. In that case the AC would work harder in winter time (this is an SDS controllable setting).

Your car anyway would already have a continuously running compressor, it is not driven by an electrically controlled clutch drive. The compressor is driven even in off mode, the drive shaft would turn but the compression function would be turned off by other means.

Older compressors were also prone to leak if the compressor was not used for long periods. This was specifically before ceramic seals were used. I guess it still today would be advantageous to run the compressor every now and then during winter (if temperatures are below +4, one would need to run the compressor at a warm parking lot or similar).

The car cannot produce heat from the engine before the engine gets warmed up. However a CDI wold have an electric heater element, you can feel heat almost immediately even if this isn't as powerful as the water heater core. Note that the electric heater is switched off if the AC is set off manually! MB has later on advised to set this setting differently, in a way that the electric heater would be active (when cold) irrespectively of the AC setting.

If you want to learn more (and perhaps get corrections to what I wrote), I could send a document covering the A/C system on several modern MB models.

 

Thanks for the info. This is happening when the outside temp is somewhere around 50 degrees F, I set the inside temp to 72. Push Auto, and the unit blows cold air as if the AC where on (which it must be as the AC Off light is not lit. I guess the aux heater element will not come on at 50 so I have to wait until the engine warms up to get heat.