I have a mr slim msz 36na out door unit combined with 4 indoor units 3 of them are 9000 btu and the one for my living/ dining room area is 15000btu. A week ago i noticed that the 15000btu unit had hardly any airflow going though it. So i opened the unit up and noticed the fan was covered with dust. I then cleaned the dust off of the fan and the coil. Now with everything cleaned up the blower is still not blowing the same amount of air that it used to and also the fan is making a pulsating sound. could it be that due to the lack of maintenance on the unit the collection of dirt and dust on the coils and fan has caused the fan motor to start to fail? Also how long the a mrslim indoor fan usually last and are the parts expensive?