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Problem: My outside AC unit is humming but no fan or compressor action. Sounds like I have a capacitor problem?

Problem: My outside AC unit is humming but no fan or compressor action. Sounds like AC problem #1, capacitors. I’d like to buy replacement capacitors but they are round. Can I use oval caps with the same rating? Can I leave them loose since the brackets are for round caps?

I need the following:
qty 1 40 uF / 440 V (round) No 40 / 440 on your website. Can I use a higher cap single below?
45 MFD 440 Volt Oval Run Capacitor Price $22.00 Each
qty 1 5 uF / 370 V (round) You have 5 MFD 370 Volt Oval Run Capacitor Price $8.00 Each

Finally, can I replace the two caps with a single dual cap? 40/5 MFD 440 Volt Dual Oval Run Capacitor Price $30.00 each?

Answer: Thanks for your kind words and interest in our web site! Below we have a real good YouTube video made by DIY Tinker on troubleshooting a capacitor and what to look for if the AC unit is not coming on.  Since your fan and compressor are not running I would like to suggest that you test the line voltage with a meter to see if you have 220 to 245 volts on L1 and L2 of your contactor. Another question is: Are the contacts on your contactor closing when your air conditioner is calling for cooling? You should be getting 24 to 28 volts to your contactor’s coil when your thermostat is calling for cooling. If your contactor is closing and you are getting voltage 220 to 245 volts through the contactor then this could be a capacitor problem. If you are not getting 24 volts to the contactor then you might have a thermostat problem, thermostat low voltage wiring problem or an air conditioner safety control (if equipped) problem. Some units have a high and low pressure switches on them that will not allow the unit to come on if the pressure is too high or too low (low refrigerant charge) in the system.

If you understand the electrical wiring it would be the easiest to purchase a dual 40/5 MFD 440 volt dual capacitor. There are three connections on a dual capacitor. Com, Herm, & Fan. Common (COM) on the capacitor would come from your power source usually from the contactor. Herm connection would go to the start winding on your compressor, Fan would go to the fan, usually a brown wire. If you are not accustomed to doing the wiring then I would suggest sticking with the same capacitor. It is not recommended to replace a 40 MFD capacitor with a 45 MFD capacitor. I am going to add a 40 MFD, 440 volt capacitor to our site this morning if you want to purchase the 40 MFD 440. We sell all different types of capacitors on the following page: Please click here to see all the capacitors we sell.

Since you have round capacitors (nice pictures) and the ones we sell are all oval you would need to make a mounting strap out of plumber’s pipe strap. I can send you some of the pipe strap in the order if you will say, “Pipe Strap” in the comments section of our cart. You would need to secure the capacitors so the wire terminals do not touch anything metal or each other. I usually tape the connections on top of the capacitor with electrical tape and secure the capacitors to the frame with plumber’s pipe strap. Make sure you do not drill through your condenser coil. If you have any other questions please feel free to email us at: or comment in the comments section below. We would love to help you out and have your business!
Thanks for the opportunity to do business with you! I hope you have a nice day!

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