Why is only one of my vents blowing cold air the others are blowing relatively warm compared to that one I just replaced the blower motor and the cabin air filter

 

Probably a stuck or broken blend door actuator. Try moving temps way low and way high several times to see if it loosens it.

 

did it like 20 times still same and also the car has freeon and the ac is just not freezing like it should be I also own a 2008 Mercedes c300 and it gets so cold I have to turn down the ac this one does not do that

 

Do you have a diagnostic tool to read the codes? I forgot, also try moving the air around from the various vents too. I know you probably already did that but just want to be sure.

 

Sound like your A/c system is having problems. Normally, only one vent blow cool air, and other is warm is sign of lack gas in your A/c system. Check your gas, good luck.

 

There is only one evaporator coil for the A/C to cool the car unless you have the dual system that I think has another one for the rear passengers.

If the coil provides cold air for one vent it means it provides it also for all vents that the system settings ask for. It is NOT about low refrigerant in the A/C system, It is about the air flow mixer valves that control air temperature coming out of the vents.

 

W212 sedan has only one coil. If the setting of system has problem, you will get code with xentry or other code reader as Thinktool ... As BMW, only one vent has cool air, in bmw is driver side, and MB as I remember is passenger side is low refrigerant. If low, you must find the leak point to fix this problem, don't only push more gas to your system.

 

Driver and passenger sides are NOT separate. If you get cold out of one, you get it out of the other unless the blender door for the passenger side is malfunctioning. Use a Mercedes specific scanner to check for errors. Then you can begin to address the problem.

 

You need to use diagnostic tools. By "feeling" you are not going to find the problem.

You can:
1 - Get an MB-aware scanner and monitor live data. Also having a set of AC pressure gauges ("free rental" from AutoZone/Advance AutoParts, else)
2 - From the live data check the evaporator temperature when set ot MAXCool, and the engine @1500RPM
3 - Check voltage at the blower is its maximum; otherwise, the blower is not being commanded or it has a regulator problem
4 - If the evaporator temperature reaches @5C or less, your "refrigerant cooling system" is just fine --> focus on air distribution in the cabin (as suggested by several above)

As with any diagnosis: proper tooling, and the ability to dissect the system somewhere, so you can trace back, or follow forward. Without a reference point to make decisions, it becomes guessing.