My outside condenser fan quit running, so I tested the capacitor, and got nothing on the meter. The cap that was in there was a 35/7.5. The closest one I could find at the time was a 50/7.5. Now that the new capacitor is installed the fan runs, but it is taking a very long time for it to cool down the house. It will not get below 75 even though the thermostat is set to 68, for testing.

I was thinking that it may be low on refrigerant, but it cooled fine before the capacitor went bad. I don't have any gauges to check pressures.

Would the difference in the capacitor cause this, and is it safe to continue to run the condenser with that capacitor?


Installed the new correct capacitor, and cleaned out the condenser coils. Also had an HVAC person check the charge, which was fine. Now the unit is working perfect.

Thank you to everyone that has helped.

  • It depends. You would need to shoot us a photo of the old and new caps so we can read the data off it ourselves. 50/7.5 is not a capacitor specification. Some specs must match, others can flex. – Harper - Reinstate Monica Aug 9 '19 at 17:45
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    50/7.5 is a dual element cap usually called Start/run. The 50= 50 micro farads 7.5 is 7.5 micro farads usually at 360 or higher volts You can use larger voltage but should be within 10% of The capacitance value in this case expressed in uF. – Ed Beal Aug 9 '19 at 18:06

Normally you need to stay within 10% of the capacitance. Having a start run you can be a bit more off but since your run value is dead on I would think your refrigerant charge is low. Many times when I find cap problems the systems are older and are a bit low on charge. This is not always the case but many times it is. 50uf is a bit high and is creating a larger phase shift than is needed but if the system is getting to speed and you can verify this with a tachometer I would not be worried about the cap value of not getting to speed it will cause excess heat buildup in the motor and early failure. FYI there are very inexpensive tachometers both optical and mechanical on line this is about the only way to know for sure.

  • Thank you for the reply. I will get someone to come out and check the pressures and charge if it is needed. I have a new capacitor with the correct rating on the way. – Michael Gelbart Aug 9 '19 at 16:03

I would not run it like that! the 50/7.5 is making the fan run great because that is the correct number it's calling for. putting 50 on a 35 compressor will overload it and potentially cause a bigger issue. they sell universal capacitors that are perfect for situations like this.

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    Thank you for the reply, I found a 35/7.5, and should be here tomorrow. Could the bigger capacitor cause it not to cool correctly? – Michael Gelbart Aug 9 '19 at 15:23

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