Near the bottom of this page we have a real good Youtube Video made by Acservicetech that shows how to troubleshoot an air conditioner if the air conditioner outside unit is not turning on. Many thanks to the AC Service Tech Channel!
Problem: This problem is probably the second most common problem that I see every summer in our HVAC business. The problem most of the time is a bad run capacitor. The Air conditioner outdoor unit will not come on. Either the outdoor fan does not run, the compressor does not run, or both the fan and the compressor do not run.
Solution: You probably need a new run capacitor. We have a real good air conditioning troubleshooting YouTube video near the bottom of this page that ucberk599 produced. This video discusses and shows how to install a new capacitor. Please click here if you would like to see the capacitors we sell.
1. I would first recommend turning your thermostat to Off and then reset your air conditioner’s circuit breaker. Most of the time home air conditioners run on a 30 or 40 amp double pole breaker. Always were shoes and do not touch any metal part of the breaker box when resetting a circuit breaker. Reset the circuit breaker with two fingers on the breaker handle only. Below grayfurnaceman made a video on how to check to see if there is power coming from the disconnect box to your air conditioner’s contactor. I have seen people have one hand leaning on the breaker box and the other hand resetting the breaker!Do not do this because you are grounding yourself through the breaker box and if there is a problem with the breaker or box then you could get shocked! Even if the breaker looks like it is OK still flip the breaker all the way off and back on again. I have had many customers over the years that say their circuit breaker is ON and OK, but when I drive to their home and reset the breaker the air conditioner starts! I hate to charge them a service call when all I had to do is reset a breaker!
2. You have reset the breaker and the outdoor unit still does not come on. You turn the thermostat back down so the air conditioner is supposed to be running and you go back outside to the unit. You can hear a little humming sound, sometimes a “Uggg” inside the unit when power is applied. The “Uggg” is probably the compressor trying to start. You might hear the low voltage contactor humming. You pull the disconnect and disconnect the power to your outdoor air conditioning unit. Please make sure your electrical power is off before working on any air conditioning equipment. You take the door or cover off your outdoor unit’s control box and find that the contactor is engaged meaning that the contactor is getting low voltage from the thermostat and low voltage controls. If the contactor is not engaged (contacts not pulled down) then you have a low voltage problem which could be in the thermostat, thermostat wires or your air conditioner’s safety controls. On some air conditions the manufacturer’s install high and low pressure safety switches to protect the unit if the pressures get too high or too low. If your unit is low on refrigerant the low safety switch will not allow the unit to come on. If your unit is real dirty of if the fan motor stops the high pressure switch will stop the unit until it is reset. If your contactor contacts are not engaged then it could be a thermostat or safety control problem. Please make sure that the batteries are good if your thermostat uses batteries. I have seen low batteries cause this problem.
3. The contactors contacts are closed (engaged). Everything is OK with the contactor. Now you take a look at the capacitor/capacitors and find a bad, swollen run capacitor. If you find that your capacitor is swollen then you have found the problem of why your unit will not run! Congratulations! EPA stopped allowing manufacturers to produce capacitors with cancer causing PCB’s back in the 1990’s. Since they stopped allowing the use of PCB’s the capacitors now have a shelf life. Many times I see capacitor problems that will not allow the compressor or the fan to come on . Many times you can clearly see that the capacitor is bad because it is swollen or even blown apart with capacitor oil everywhere! Sometimes you will need a special meter to test the microfarad (MFD) or (uf) rating. “MFD” and “uf” mean the same. Some capacitors will have “MFD” on them and some will use “uf”. Most of the time you can tell the capacitor is bad because it is swollen up. Please see the pictures below for the comparison between a good and bad dual run capacitor. Capacitors are called “Dual” because the capacitor helps run both the fan and the compressor. Dual capacitors will have three areas where wires can be hooked up. The terminals are labeled: Fan, C (Com) and Herm. If you need a new capacitor we sell capacitors on the following page: Please click her to see all the capacitors we sell index page. You will need to know the MFD rating or uf rating and the voltage rating. This should be clearly visible on the label of the capacitor. If you do not have a capacitor tester you may be able to take the capacitor to a local appliance repair parts store and ask them to test it for you. We sell a capacitor tester on the following page: Please click here to see the Supco MFD10 capacitor tester we sell. If you do not know what size capacitor you unit uses you can email us with your unit’s model number and we will try to find out which capacitor your unit uses. Our email address is: firstname.lastname@example.org We would love to help you out and have your business!