Door closers come in different styles, but they all work in the same way. You attach one end of the closer to the door, and the other end to the door frame, and when you open the door and release it, the closer pulls the door closed while preventing it from slamming. The closer can do this because it has a sealed tube that contains a pneumatic spring. In order for the closer to work properly, you will have to make a few adjustments to the mechanism after you install it.
Open the door closer packaging and find the instruction manual. The method of installation will vary according to the model you buy, so read the instructions before you proceed.
Position a ladder in the door frame and climb high enough so you can work comfortably without reaching up. This will make it easier to apply the force necessary to drive the screws.
Attach one end of the closer to the top of the door according to the instructions. Some closers have screw holes in the spring cartridge for this purpose, and some have an arm extending from the cartridge with a plate containing screw holes. Use the screws that are provided with the closer.
Screw the other arm to the door casing or door jamb, either at the top of the door in the middle or over to the side, depending on the model. When the closer is installed, try the door.
Look for adjustment screws on the spring cartridge and verify you have the correct tool to turn these. If the screws do not have Phillips or slot heads, the tool you need will probably be an Allen wrench, and this should be provided with the closer.
Adjust the swing speed screw to control how fast the door closes from fully open to about -15 degrees Crom closed. Turn the screw clockwise in increments of 1/8 of a full turn to decrease this speed and counter-clockwise to increase it.
Adjust the latching speed screw to control how fast the door closes from 5 degrees closed to fully closed. Turn the screw clockwise in increments of 1/8 of a full turn to decrease this speed and counter-clockwise to increase it.
Adjust the back check screw to control the amount of force needed to open the door. Turn the screw clockwise to increase this and counter-clockwise to decrease it.
Make adjustments to the spring tension by turning the knob on the end or side of the spring cartridge. This knob should be used for fine tuning only. Tightening it too much can make the door difficult to open.
If you are making adjustments to an old door closer and you notice it is leaking oil, then this means the hydraulic seal is broken, and you should replace the closer.
Never try to repair a closer by disassembling the spring cartridge. The spring is loaded under pressure and can injure you when it is released.