Home air conditioners were first developed in the early 1900s, and they're usually very efficient. However, like any appliance, an air conditioning or heating unit can develop electrical or mechanical problems. You can troubleshoot your own unit, and fix minor problems, but others will require professional repair. Following are some common problems and how to fix them. Home Air Conditioning Problems
First, check the power. Has the circuit breaker tripped, or a fuse burned out? Obviously, the solution is to reset the breaker or replace the fuse. Some units will have a breaker panel located outside - make sure that the breaker is on and that the "quick disconnect" isn't improperly inserted. If this doesn't correct the problem, check the thermostat. Set it several degrees below room temperature, and wait for the unit to activate. If this doesn't work, you'll need to have a technician replace the thermostat. The Unit Won't Turn On
If the unit is running continuously, it's possible that it's just too small for the room. Alternatively, if it's constantly cycling on and off, it could be too big. A faulty relay switch or low refrigerant level can also cause constant running. If the problem is the size of the unit, then obviously you need to get a unit that's more appropriate for the room. If it's the relay switch, a technician can replace it for you. The Unit Won't Turn Off
This problem is usually due to bad air flow. Make sure your filters are in good condition - clean them, or replace them. A unit can also freeze due to a malfunctioning blower fan or a faulty control relay. When this happens, the outside unit will keep running even when the inside unit is off. Faulty components will have to be replaced by a technician. The Unit Freezes Up
Again, the problem could be due to dirty filters. It's not that the unit isn't generating cold air, it's just that it's not flowing properly. The solution is to clean the filters. Another reason for warm air could be lack of refrigerant. You'll need a technician to top up the coolant. The Unit is Blowing Warm Air
As with most appliances, you can do minor servicing on your own. For more serious problems, call a specialist. Home Heating Problems If your furnace is turned on, but there's no heat at all, the first thing to check is your electrical power. Make sure the circuit breaker hasn't tripped. If you re-set it and it trips again, you may need an electrician. DIY, or Call a Pro?
Is the pilot light igniting? If it's off, you can re-light it. The flame should be blue, not yellow. Yellow could be an indication of carbon monoxide buildup, and that's very dangerous. Also, there could be a problem with the gas supply, which would indicate that a call to the gas company is in order. Generally speaking, a problem with the pilot light will require professional assistance. Also, check the thermostat. Make sure that it's set to "on," and that it's turned up high enough to activate the furnace. If none of this works, it's time to call a technician.
Resources: http://thaheatandair.com http://ezinearticles.com/?Typical-Home-Air-Conditioning-And-Heating-Problems&id=8492211