An open air damper will draw in outside air

 Loud Rattle: If the air conditioner unit has a loud rattle every time it shuts off, you may way to check the compressor mounting pads and brackets. Musty Smell: If the air from the air conditioning unit smells musty, this may be an indication that mold is growing on the moisture inside. If the other appliance works fine, you may need to consider air conditioner repair.  . This can result in moisture collection in the bottom pan of the unit and it may build up over time. Air conditioner repair technicians will inform you that this helps prevent mold or mildew from growing on dust and debris that can collect. While this problem cannot be prevented, you can dramatically reduce the chance of it occurring by cleaning out the bottom at least once a year. Water collects in the bottom of the unit and is usually evaporated, but may cause favorable conditions for mold growth. 

An open air damper will draw in outside air, while a back cover that is used for protection during the winter months must be removed in the summer. Both of these will require the skill and expertise of an air conditioner repair technician.Unit Doesn’t Turn On: Check to make sure there is sufficient power to the air conditioner unit and that all cords are intact. As long as there is no water leakage, a little sloshing is no concern and does not require air conditioner repair. If the unit is getting power, but is still dead, the problem may be with the wiring, thermostat, compressor, relay switch, or control board. You can check the electricity through the outlet by plugging in another appliance. This is likely a problem with the thermostat, air damper, back cover, or condensing coils. No Cold Air: If you notice the fan for the air conditioner is running, but there is no cold air, this may be a problem with the compressor or condenser. If the rear fan used to cool the condensing coils comes in contact with the water pan, some of the moisture will be spun from the fan blades and may cause a sloshing noise. Only Cool Air: Maybe the fan is running and the air is cool, but doesn’t feel cold enough. Most often, a loud rattle when FN Serial Air-Cooled Condenser Factory starting or stopping is due to normal motion of the powerful motor or may be due to improper or loose installation. Sloshing Water: Part of the technology that allows air conditioners to cool the air involves evaporation of moisture from the air. If these become worn or missing, it may cause excess noise when the unit starts up or shuts off. Constant Running: If you notice your air conditioning unit is constantly running and does not shut off, it could be one of many problems. Ensure the air is cold enough to cool the room to the temperature you desire. Ensure the room to be cooled has adequate shade or sunlight blockage in order to increase the efficiency of the cooling system