Central air problem


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Old 07-18-12, 07:45 AM
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Central air problem

Had an issue with my older Trane central a/c unit yesterday. It's been running fine the few times it's been used this year until last night. When I got home and it wasn't as cool as it should have been I looked and noticed the cooling fan over the compressor was not working. It was making a humm, but not spinning. I then gave the blades a good spin by hand and the motor kicked right over and started working normally (so I know that the motor will need to be replaced soon). But after that the unit still was not cooling the house. Did something fry itself since the cooling fan was not working? The unit seems to respond correctly when the t-stat tells it to turn on and off. I did not see anything damaged when I took the cover off. Any help would be great! Thanks.
 
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Old 07-18-12, 07:58 AM
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Since the fan started spinning....it's an indication that the capacitor is bad. Did you hear the compressor running? Your unit may use the came cap for the compressor and the fan....if it goes bad you can spin start the fan...but not the comp. You should turn everything off until you get it fixed.

You'll need to get access to the guts and look for a small round or oval "can" with wires attached. Look for bulging or an oily leakage. They will run about $30 at an HVAC or electrical supply.

Turn off all power to your A/C and furnace before doing any work. There are high voltages inside and the cap may retain a charge even with power off.
Post back before removing any wires. You'll want to make a drawing or take pics so you can replace the wires correctly.
 
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Old 07-18-12, 08:04 AM
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It sounded like only the fan was running.

Is there any way to test the capacitor? Granted it doesn't (or should maybe is the right word) cost much so I suppose it's not that big of an issue.

Would that fix the fan starting as well? From what I know just of electric motors I think it would need to be replaced as well.....?
 
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Old 07-18-12, 08:19 AM
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A failed cap is probably the most common problem found on the outdoor unit.

The fan and the comp both need a boost to get started...that's what caps do. A failed cap won't hurt the fan motor unless it just sits and hums for days possibly causing overheating. No reason to replace the motor if it runs. On the other hand...if the motor had failed...then you always want to replace an old cap with a new one specifically listed for the new motor.

You can test it...but you need a meter that can measure capacitance...most people don't have them. Some supply houses MIGHT do it...but likely not. Visual inspection is usually all it takes.
 
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Old 07-18-12, 08:33 AM
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Well I guess I'll just have to find a capacitor. Knowing my luck there won't be anyone in my area that I can pick one up from easily. Once that's done w'ell see what happens with the motor.

Thanks for you help!!
 
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Old 07-18-12, 08:42 AM
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When the condenser fan quits running the compressor will overheat & the thermal switch will open; it can take an hour or more for it to cool enough to reset & start running.

I always had a capacitor tester, however, the Supply House might check it for you.

Capacitors can hold a charge even after the power has be cut-off, so with power off using an insulated screw driver short across the terminals.

If the capacitor tests good, the motor could be going bad.
 

Last edited by HVAC RETIRED; 07-18-12 at 08:44 AM. Reason: Clarity...
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Old 07-18-12, 08:46 AM
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Before you start calling around...you'll need to get the specs off the old one.
 
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Old 07-19-12, 10:58 AM
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Thanks!!!!! $30 and a quick 5 minute fix and it's back up and running!! Got lucky that there is a Trane parts dealer 20 mins from my house.

Thanks again!!!
 
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Old 07-19-12, 12:41 PM
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Very nice...keep the number of that place. If they are an HVAC install and repair company (not a supply house) and sold you one for $30...I think they gave you a good price. That tells me honesty and fairness is important.

If it was a supply house...keep the number anyway...like I said that's about the going rate.

I needed a cap for my garage door opener and called a local "repair company" telling them the part I needed. The guy I spoke with said it would be $60 ($15 for the part and $45 for the service call to deliver it) unless I wanted to wait til he happened to have a job near me. I even said I'd drive to his location to get it and he said then the cost would be $25. Say what?????

And just to be clear...the motor should be fine....but may indeed have an issue. The cap is just the most likely problem. No reason to buy a $100 motor til you know you need it.
 
 

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