Select from:
[+] If the pipe is warm to touch, the flow of air is likely dirty and needs to be replaced. Check the wires connecting the unit to the house.
[+] To use a thermometer, turn off the motor by holding the small copper pipe under the temperature set up in the unit's hood. Turn the knob on the thermometer until the temperature reaches 165f (74 c).
[+] Rake any leaves and debris away from the unit before you start to service an air conditioner. Take the cover off the unit, and locate the air conditioner coils (they look like a car radiator).
[+] Push the tongue or flathead tool close to each wire joint and loosen the loose connections. If it doesn't feel hot at all, the model of the unit is old and won't work.Choose from options above and answer: What most naturally follows?

How to service an air conditioner
Make sure the unit is turned off either at the on/off switch or by shutting off the circuit breaker.
Check the small copper pipe connecting the unit to the house.
If it feels hot, the unit's coils are most likely dirty and need to be washed.
Answer:
Rake any leaves and debris away from the unit before you start to service an air conditioner. Take the cover off the unit, and locate the air conditioner coils (they look like a car radiator).