Isn’t it time to know what you don’t know?

Click here to check out our structured, online appliance repair training courses for rookies and experienced techs.

FAQs | Repair Videos | Academy | Newsletter | Podcast | Contact

Stay connected with us...

Samurai on Facebook - become a fan today! Sign up for our free newsletter and keep up with all things Appliantology. Subscribe to our YouTube channel for lots of appliance repair tips and help! Follow the Samurai on Twitter and get timely morsels of Appliantological Wisdom! Subscribe to our MST Radio podcast to learn secrets of the trade.
  • Announcements

NickG

Lennox AC unit HS20-311-1P just hums

18 posts in this topic

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

 

 

 

 

Share this post


Link to post
Share on other sites

Need appliance parts? Call 877-803-7957 now!

Change the Fan Capacitor

Share this post


Link to post
Share on other sites

Check the capacitor on the "outside" unit

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

This site will link you to parts.

 

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

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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!

Share this post


Link to post
Share on other sites

Got the new capcitor.  No difference. 

Share this post


Link to post
Share on other sites

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. 

 

 

Share this post


Link to post
Share on other sites

May want to check the contactor like I suggested :)

Share this post


Link to post
Share on other sites

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.   

Share this post


Link to post
Share on other sites

 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 by Ghost

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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 by BryanS

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now