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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 852
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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First of all, I know nothing about central A/C systems. Ours

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First of all, I know nothing about central A/C systems. Ours is trying to cycle. It tries to come on repeatedly (every few minutes), but within seconds, it shuts off. A little bit of cool air is coming through the inside fan, but the house isn't cooling to the temperature the thermostat is set to. But the outside fan isn't kicking in. It makes a noise that's louder than usual while trying to turn on, but the fan doesn't turn at all. Would you be able to tell what's going on? If so, is it something I can fix? Or, is it going to be costly?
Hi, I'm Brian. I'm here to answer your HVAC question to your complete satisfaction!

Your outdoor fan should come on as soon as the unit is called to run. Since it isn't the compressor only runs for a short time before a protection device shuts it off. It could be something as simple as the fan motor run capacitor. A ten dollar (or less) part available on the internet or a local appliance parts store. That is something a homeowner can easily replace if comfortable working inside the unit control panel. It could also be the motor windings have burnt out or the motor bearings have seized. If you can easily turn the fan blade manually with a long screwdriver stuck through the grill that will tell you if the bearings are seized. If they are not seized it will either be the fan motor capacitor or the fan motor itself that has failed. That requires a multimeter with a capacitance scale to determine for sure. You could try just replacing the fan motor capacitor to see if that solves the problem. Sometimes a failed capacitor (a small cylindrical oval or round can looking device in the unit control panel) will show that it has failed by the top of it being bulged where the wires connect to it. If your fan motor has failed a service company will charge somewhere in the area of $400 to replace it.
Customer: replied 3 years ago.

Alright, I tried turning the fan blades manually and they turn fine. So with your help I looked up failed capacitors and found a site that suggested 'starting' the fan blades turning with a stick. That got the fan running on its own just fine, and now it's working, so that must mean it's the capacitor, right? I can't try replacing it until Wednesday, but will buy the part tomorrow hopefully.


 


So two questions. Is there a specific kind of capacitor or something that I need to buy? I don't know where to find the model number of our unit because there's different numbers everywhere.


 


Second, any words of wisdom on replacing this? I've never done anything with the unit control panel but would like to try.


 


Thanks for your help; it's a huge relief to not have it be the motor.

That is good news! Yes under those circumstances it is most probably the fan motor run capacitor. You don't really need the unit model number to get a replacement. If you are going to an appliance parts outlet to buy the part you can simply take the old one with you. If you are going to buy it over the internet all you need is the Mfd (microfarad) rating of the capacitor and the voltage rating. You can go from a 370 volt capacitor to a 440 volt capacitor as long as the Mfd rating is the same but you should never use a lower voltage rated capacitor. Most a/c units today use what is referred to as a "dual run capacitor" that is a capacitor that has 3 terminals on it and is used for both the fan motor and the compressor. That capacitor will run a little higher in cost than a fan motor capacitor alone and you should replace it with like for like. It also doesn't matter if the capacitor is larger or smaller in physical size as long as the ratings are correct and the capacitor is not too big to fit where the existing one is. A typical dual run capacitor will have a rating such as 35/5 Mfd (or uf) at 370 or 440 volts ac. When removing the old capacitor it is wise to snap some pictures of it before you start, paying careful attention to which wires are connected to which terminals. You also need to make sure the power is off and you discharge the capacitor by shorting all the capacitor terminals to the unit casing with the shaft of a screwdriver. Make sure not to touch the shaft of the screwdriver while doing so or you may get a nasty shock even when the power is off because capacitors can hold their charge especially failed ones.
Customer: replied 3 years ago.

Ok, I think we understand everything you've told us. I'm fairly certain we can handle changing out the capacitor.


Is it ok if we keep you on stand-by on Wed or Thurs?

That is certainly ok with me but bear in mind even if you do rate me now I never close my questions and I am always available for follow up questions about the same issue on the same question at no additional charge. Good luck and be safe!
Brian HVAC Guy and 3 other HVAC Specialists are ready to help you
Customer: replied 3 years ago.

I just wanted to let you know that we did manage to replace the capacitor and our A/C is working now. We did have a bit of trouble finding the capacitor - ended up buying one off a contractor. But thanks to you, we were able to save over $100. So again, thank you so much!

That is great news! I'm really glad I was able to help! Feel free to look me up if you ever have any more heating or cooling problems. Take care and thanks, -Brian

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