You turn on the thermostat for your Central Air Conditioner. Instead of cool air, you get warm air coming from the vents. You go outside to see if the fan on the compressor is running. It is not. Before you call the repairman, there is something you can try, to fix the A/C yourself. DIY Air Conditioner repair. This happened to me recently. Of course it was a really hot day and I had nothing to loose.
First off, I am not an electrician or A/C technician. The circuits are high voltage and if you do something stupid like work on equipment with the power on , and the voltage goes through your heart, stopping it, you could die! Do not attempt if you have any doubts.
You are going to check the fuses. Before that, check that the circuit breaker at the main panel is not tripped for the A/C. Reset it if it is. Central Air is usually the second largest breaker in the panel. In this case it is a 50 amp breaker in a 100 amp panel. Then try turning on the A/C at the thermostat. If it works, great you are done. If it keeps on tripping the breaker, call a repairman. If the breaker is fine, check the fuses next to the compressor. (Turn off the circuit breaker first!) Here is the fuse box next to mine. This setup is safe to work on, as the whole fuse-block pulls straight out. Yours may be different. Mark which side is up to make it easy to re-insert correctly.
Flipping it over you see the fuses in the block. This is a 220 Volt circuit so there are two. Fuses can go bad over time, because of heating and cooling. Like a light bulb. To test the fuses I am using volt/ohm meter. Any do-it yourself handy person should have one of these. This is a $5 one from Harbor Freight. They sell them at Walmart too. In this case I am using it to check continuity.
Using the 200 ohm scale (the scale with the omega symbol) I clip the leads to each end of one fuse. Do not hold in place with your fingers, you will get a false reading! This fuse is reading 3.4 ohms resistance. So this fuse is OK. Current can flow through it. Checking the next one the meter reads a “1” all the way to the left. This means the fuse is blown. No current can flow through it. If this is the case for you. You have found the culprit. Replace the fuse with the same type. Pry out the blown fuse out of the clip and take it to the store and match it. In this case it is a slow blow fuse. They cost more than the regular ones, but that is what is needed.
After you insert the new one, put the block back into the box, close the lid, turn back on the breaker and see if the A/C works. If it does hooray! If not, or it works for awhile and blows the fuse again, or the fuses tested okay- call a repairman.
Another thing it can be is the contactor or relay inside the unit. I have had ants crawl in there and foul it up. But, that is more involved than I can get into on this blog. There may be a video on you tube if you want to tackle it.