Duo-Therm Humming?

[badkat]

Our AC works great for a few hours then starts to hum and not work. After it is off for hours it works great again.

What is up with that?

[xrvr]

If you are running it on low fan it could be freezing up. Try high fan.

[Belegedhel]

Sounds like a bad starting capacitor on the compressor. When you say it hums and doesn't work, does the fan keep blowing, but the air is no longer cooled, or does the whole thing go dead and sits there humming until you turn it off? Does it throw a breaker when it is in humming mode?

[badkat]

It hums and no air is coming out. The fan is on auto. Guess I can try high fan. It does not throw a breaker. Actually at 2 am it was humming and it shut down humming before I turned it off.

[ShinyPete]

Why does it hum? Because it doesn't know the words. Sorry, bad early morning humor.

I actually would think the humming is the compressor still running as the thermostat is still calling for cooling, with the FAN having quit on you.......... Fan motor may be failing, it may have debris in the fan housing causing it to "drag" some and get hot and eventually fail, or something along those lines.

Anyhow, it sounds as if pulling the outside shroud off and took a look (or having a trained professional do that) would be next. Be careful - on a ladder, on the AS if necessary, running the unit with the shroud off, all that can be dangerous.

Hope this helps.

[badkat]

The fan motor was replaced a couple of years ago. Last nite I put the thermostat on low fan and it cycled on and off and no hum. When it is on auto is when the humming comes on after a few hours of use. Fan seems to work great.

[Belegedhel]

I'll stick with my earlier suggestion--weak starting capacitor. I hae a similar problem with my AC. As long as it is running in "max-cool" mode, where the compressor doesn't cycle on and off, it is fine. If I let it run for a while (ie., compressor gets hot), then turn the "cooling" to mid range (where the compressor will start to cycle on and off to maintain the temperature), the first time it cycles off, it struggles to get started again (the dreaded HUMMMMM), and then the breaker trips.