Question about Heating & Cooling

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I. The outdoor heat-exchanger fan runs at a low speed (with a humming noise), when the home temperature is below the set-point. ii. When home temp. in high, fan runs at full speed, like normal. iii. When A/C breaker is shutoff (in main switchboard), the fan stops. Need help diagnose the problem.

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  • firoz_ara Jun 28, 2008

    Dear Tactup, Thanks for the response.

    I have an split A/C unit, as you rightly guessed.
    Make: Goodman Mfg. Co. L.P
    Model: CKB18-1

    If the capacitor is busted, the condenser fan would not run at rated speed any time. The fan runs at full speed on cooling cycle and cools the house. The fan does not stop when the cooling cycle ends, but continues to run at low speed, with a humming noise.

    Hope I have stated the problem a little better. Hoping for your help.

    You can suggest more technical diagnostics, as I am a hands-on electrical guy.




2 Answers

It could also be the contactor; basically an electrically-controlled switch that in turn controls the compressor and the condenser fan. If it's a 220 volt motor, and one side of the contactor has very high resistance, it'll be seeing 110 volts instead, basically causing it to either run at roughly half speed or just sit and stutter, or other weird random stuff. Depending on the contactor design, you might be able to get an emery board (yes, for fingernails--they work great!) between the contacts and lightly buff them. Of course make sure the breaker that feeds the unit is turned off and tagged out first! Barring that, I'd check - in order - the capacitor and the fan motor itself.

And just to rule it out, go through and make sure that each end of every wire is firmly attached to whatever it's attached to. Over time those quick-disconnect connectors can work loose, causing again all manner of random stuff to happen. If you find a loose one, you can probably use a pair of pliers and gently squeeze the connector tight again. Of course make sure the breaker is off and tagged before you stick your fingers in there...220 volts WILL send you flying. Or just kill you.

The 60Hz shuffle is no fun at all. Be safe.

Posted on Jul 28, 2008

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I am not sure what kind of air conditioner that this is. If it is a split system A/C then the outdoor exhaust fan should always spin at the same RPM. So if your fan is spinning slowly and humming, it is probably the run capacitor. I will bet that the capacitor is leaking oil or ballooned out. It most cases this is a combination capacitor that runs both the compressor and the exhaust fan. It should be replaced. This usually happens as a result of excess heat or normal wear and tear. After it is replaced it will be a good idea to have the system checked out to make sure the condenser is exhausting the heat correctly.

Posted on Jun 27, 2008


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