Here is a few basic principles for air conditioner troubleshooting. For both the central home air conditioner and the window air conditioners, the very first thing that you need to check is whether the unit gets proper power. If the unit is using a power of 220 volts, you will have to make sure that the proper voltage is getting into the unit. Same for 110 volt units. A voltage meter will be used to assure you that the voltage is the correct one.
For those air conditioning units, the voltage also need to be checked before and after the thermostat. If voltage is being supplied to the thermostat but not from it then the thermostat probably needs replaced. This may be a very common problem. Another place for you to check is the fan motor voltage. The fan on window air conditioners runs both the indoor blower and the condenser fan. If that motor fails, then its compressor may only just run for a very short time; however, it will overheat and then shut off. Continued operation like this will result in compressor failure. This motor will also be replaced economically for a larger window air conditioners; but for the much smaller ones, the cost of replacement can be more than one brand new unit.
The central air conditioners for the home are way more complex, and there are also more things that might just go wrong. As with the window air conditioner, the thermostat may become a problem. The central air conditioner thermostat will only be having a 24 volts power going to it. So don't look for high voltage there. Some units the voltage will be coming from the outdoor unit and others the voltage will be supplied by the indoor air handler or furnace. Most home central air conditioning may be supplied by the indoor air handler or just the furnnace. If the air conditioner is designed for cooling, then only the unit will usually have the two wires to the condenser unit. You will then need to makike certain that you have 24 volts across those wires.
As you can see there are some simple things that a good handyman or homeowner can check. There are also some things that will require the specialized tools and experience of the professional.
