Lennox AC unit HS20-311-1P just hums

[NickG]

The site has yet to fail me.  This unti is old.  However, until Sunday, worked great.  I'm willing to nurse it to September if a small investment of time and money will get it there.

 

When the AC is turned on at the thermostat, the blower in the furnace kicks on, but the AC unit "clicks" once, then "hums".  The fan blades turn freely with a push.

 

Is there an order of things to check before I just start "replacing stuff".  Thanks!!!

 

Lennox AC unit Model # HS20-311-1P

 

 

 

 

[Bobice]

Change the Fan Capacitor

[weswayne]

Check the capacitor on the "outside" unit

[NickG]

Will do.  Thanks!

[NickG]

Does this site not sell lennox parts?  When I type in "HS20-311-1P" I get "hose 311" does not have results.

[weswayne]

This site will link you to parts.

 

You may have to search for a specific part number for the capacitor.

[NickG]

I do not have a proper tester and my capacitor is not bulging or leaking.  Since I'd have to buy a tester anyway, I'm thinking of buying the capacitor and taking a chance unless there is something else you would look at first?

Again, the furnace blower runs, the outside unit makes a click noise, then I hear a faint humming.  Nothing else happens.

Also, when I discharged the capacitor, should I have seen any sparks or noticed and obvious sign of discharge?

[BryanS]

They rarely ever spark when discharging. I've yet to have one spark on an a/c unit. I've had them spark on washer capacitors. Is the compressor and the fan not running? You may have a bad contactor. I've seen plenty of contactors closing but the contacts are worn and not sending enough power through.

[NickG]

Nothing is running except the furnace blower/fan.  The A/C unit outside just clicks once and them emits a constant low hum/buzzing.

[BryanS]

The click is probably the contactor closing. You would need a voltmeter to check voltage in and out. Plus the capacitor needs checked. It could be either one.

[NickG]

I took a shot and ordered the Capacitor.  I am learning as I go, so now I will check into the contactor thing you speak of

 

Thanks again!

[NickG]

Got the new capcitor.  No difference. 

[alamo1718]

Check high voltage line and load side of contactor. Replace if needed.

Double check the proper wiring of capacitor

Double check proper mfd rating of capacitor

Does the unit have a low pressure switch, the click hum makes be believe it doesn't. 

My google result said it has a discharge thermostat. It might be bad. 

It's most likely a capacitor or contactor issue. 

 

 

[BryanS]

May want to check the contactor like I suggested

[ACtechGUY]

May want to check the contactor like I suggested

Gosh , it sure sounds like the condenser isn't getting power to it. I would bet that the hum is just the typical buzz a contactor can make when it is energized ( most of the time you cant hear the hum due to the unit running) . check for voltage at the unit disconnect.

 the only other possibility is the contactor like bryanS said. check the contact points for things like insects trapped or melted damaged points.   

[Ghost]

 I would bet that the hum is just the typical buzz a contactor can make when it is energized ( most of the time you cant hear the hum due to the unit running) .

 

----I agree totally.  Check the contacts, then the motor itself.

Edited August 8, 2015 by Ghost

[NickG]

I had decided to let this go due to summer almost being over and Michigan not getting hot.  Then I decided to see if it is something simple.   I will check the contactor.

 

But first, can you please explain something?  There are two pull "fuses" along the route to the unit.  One just off the meter, then another along the linr about halfway.  With BOTH of these pulled completely, I still get the "click/hum".  Shouldn't there be NO power at all to this thing with both of those pulled????

 

I just double checked this to and it is certainly doing this with the main and other fuses yanked out.

 

I also put my ear to the unit and it souned like the low hum/buzz is coming from the thing that all the wires go to from the capacitor.  Might that be the contactor?  I do not like the thought of removing that with it still live.  I'll remove the fuse downstairs to the furnace (yes, I still have fuses).

 

As far as checking voltage and stuff, that is out of my hands.  I don't have a voltmeter, wouldn't know what to look for, nor how to use it.  At that point, I'll leave it to the pros.

 

Thanks. 

[BryanS]

You are hearing the buzz because the contactor coil is powered by a 24v transformer from the inside unit. The coil energizes, closes, and then send the 230v through the contactor to the compressor and condenser fan motor. Need to cut power to the inside unit or turn the thermostat off.

Edited August 14, 2015 by BryanS