# Lennox A/C troubleshooting



## sirphobos1 (Jun 13, 2008)

Hi all, I just recently purchased my first house and i'm having trouble with the A/C unit outside. First off, it's a Lennox 10ACB24-11P. I'm assuming it was built with the house, in 2001.

Here's my problem. On the outside unit, when the thermostat is set to cool, and the unit turns on, after about five minutes or so, the fan will cut off, and the compressor will continue to run. Here's a list of things we've tried to troubleshoot the problem:

-replaced fan motor
-replaced cap
-cleaned contactors
-ran old motor with new cap
-disconnected compressor from power and still watched the fan stop running.
-ran separate caps for the compressor and fan, and still had the fan cut out.

i'm out of ideas. Any help would be great.


----------



## Ottawa DIYer (Jun 12, 2008)

Contact a Lennox HVAC dealer in your area? Chances are they've probably seen stuff like this before and will be able to help you out (or at least give you some sort of quote).

Of course, that's not exactly "DIY", but if you're all out of ideas, might be the best bet.


----------



## geo fan (Jun 12, 2008)

*motor hp size*

I have seen this before your fan is over heating and going off on thermal over load contact tech support of the equip with the model and serial ready and find out the RIGHT size motor and where it can be ordered say you would prefer a direct replacment and not a rescue motor


----------



## 8 Ball (May 17, 2008)

Where are you losing power? Take voltage reading where the motor leads are connected when the fan stops running.

Measure fan amperage when the fan IS running, compare to the motor rating tag on the motor.

Measure the amperage at the disconect when both are running, compare to rating tag on the condensor.

Disconnect power to the condensor when the fan quits. Is the motor hot or cool?


----------



## troubleseeker (Sep 25, 2006)

Be sure you have the correct replacement motor for that unit. I had that same type of problem with my Lennox after replacing the fan motor. Brought the motor back to dealer and got another one, and did the same thing. Finally when I mentioned that the fan seemed to be turning faster that I remember it used to, the actually looked up the replacement motor, instead of just grabbing a 1/4 hp replacemenet motor. Turns out that the correct motor was indeed a 300 rpm slower motor, with a higher torque rating to handle the high pitch in the particular fan blade for my model. Exactly as geo fan said; the motor had insufficient torque, so it was under extra strain, and would overheat and shut down.


----------



## sirphobos1 (Jun 13, 2008)

Ran another test last night with another new cap, and original motor. put meter on contactor, showed a steady 238 vac, with occasional 239. still retained 238vac after fan kicked off. took much longer to do, either on account of it not being as hot, or some other reason.

i'm starting to lean towards the motor is crap, and the one we got to replace it was the wrong one....


----------



## 8 Ball (May 17, 2008)

Voltage sounds fine, however, amperage tells the tale. If your not too frustrated by now, measure the amperage then compare it to the nameplate rating FLA on the motor. Anything over the FLA will cause the motor to overheat and trip its internal overload.


----------



## sirphobos1 (Jun 13, 2008)

that will be the next thing i check.... luckily, it's been in the mid 70's here all week so I haven't been hurting for air.


----------



## apple roof cleaning (Mar 12, 2008)

My brother owns an Air Conditioning Company In Tampa FL
I bet he would know, since he is an A/C Contractor.


----------



## sirphobos1 (Jun 13, 2008)

i had an HVAC specialist come over last friday and look at it. He declared it was the motor, and said that more than likely i had been given a bad replacement motor, so I have a new one on the way. another update when i get this motor installed...


----------



## sirphobos1 (Jun 13, 2008)

Air's been running healthy for the past 15 hours now. it's nice to finally have working A/C. It was in fact the motor the whole time. Apparently the replacement was bad?


----------



## 8 Ball (May 17, 2008)

Thanks for the closure. Was a great post. Glad everything is working well.


----------



## actec (Jun 22, 2010)

Make sure its the right replacement 

years ago ran into the same thing, (keeprite unit ) needed ball bearing mtr


----------



## beenthere (Oct 11, 2008)

I hope he got it working in the 2 years since he started this thread.


----------



## NitrNate (May 27, 2010)

ha ha, these old threads that get bumped...gotta pay close attention to the dates. it got me too.


----------



## beenthere (Oct 11, 2008)

LOL... Lots of people forget, that when they are going back lots of pages to read post. That the further back they are. The older the post are.


----------

