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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5227
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a 8 year old 5 Ton Lennox HS26-060 Condenser unit that

Customer Question

I have a 8 year old 5 Ton Lennox HS26-060 Condenser unit that won't start. I found it off with the house circuit breakers tripped. I reset the breakers which caused the unit to make a humming noise for a few seconds and then go silent. Can't get a repair guy here for a week.

Any suggestions on how to narrow down the problem and potentially repair?
Submitted: 10 months ago.
Category: HVAC
Expert:  Phil replied 10 months ago.
.Welcome to Just Answer!

Thanks for that detailed description. That tells me that the compressor 'run capacitor' has failed, or that the compressor has failed due to burnt wire or a more severe problem with the compressor..
The run capacitors cost about $75 each and are easily replaced. Tell me how handy and safe you are working on high voltages appliances and with wiring diagrams. I might be able to coach you on further tests.


. I will stay with you until the situation resolves. I hold questions open after positive ratings to allow for unlimited follow up.

Phil
Customer: replied 10 months ago.

Phil:

I'm pretty good with electrical stuff and have a good volt/ohm/ clamp-on amp meter.

 

Edit: While I was waiting for your first reply, I flipped on the breaker again and there is no sound at all.

 

Breaker returned to off and I pulled the side panel off the unit. Nothing looks out of place, all wires good, etc.

Expert:  Phil replied 10 months ago.

Hello again,

The compressor has 3 wires attached to it, One goes to the R terminal, one to the C terminal and one to the S terminal.

Check the amperage on the wire going to the S terminal during an attempted start for just ONE second..then shut it off.

If the run capacitor has failed open, there will be no amperage on that wire. If there is amperage on that wire... turn the power off to the compressor, and verify that completely using a double checked voltage meter... then disconnect all 3 wires from the compressor, and use an ohm meter to test between each terminal and the compressor body...any read indicates a burnt out compressor.

 

If the compressor is not grounded, check for ohm readings between each combination of the C, S and R the read between S and R should add up to the total between C and R and C and S. All of those reads under 10 ohms

 

typically 3 ohms, 5 ohms and 8 ohms.

 



Look for burnt wire terminals while you are there, and look for an oily or swollen or bulged capacitor.

Caution: the run capacitors are known to explode on occasion.

We can go from there.

Phil

Customer: replied 10 months ago.

There is no AC amperage on the S terminal wire. Also there is no sound like the humming noise I heard yesterday. The capacitor looks pristine and there is no evidence of burned terminals or melted wire insulation.

Expert:  Phil replied 10 months ago.
Hello again,

Did you check amperage on the C and R wires..

if no amperage there, then either the contractor is not closing, and there is no power to the compressor ...... or there is power to the C and R terminals but the compressors internal thermal over load is open due over heating when it attempted to start last time.

It will cool off in an hour or so and you can try again.

Meantime if your multi meter has a 'capacitance' feature on it, you can check the run capacitors capacitance between its center common terminal and the terminal that has a wire going to S on the compressor. (if its just a two terminal capacitor check between them)

Do that with the power off, and the wires disconnected.

Phil
Customer: replied 10 months ago.

Phil, I just realized that with the cool morning here, the system wasn't asking for cooling when I performed the previous tests. Sorry. So, here is the revised results.


 


When switched on, the S wire amperage rises to .08 -.16 amps (not much).


 


The C and R wires are +100 amps (I didn't leave it on long enough to let the meter settle. Seems like nearly a direct short to me.


 


When powered up, there is a humming sound which I take to be a motor trying, but unable to run.


 


The capacitor does not have a "center" terminal as you described, but there is no continuity between any of the 3 terminals. Is this a failed open capacitor?


 


 

Customer: replied 10 months ago.

Phil, I went ahead and pulled the capacitor out and discovered that it is leaking a little bit - looks like oil.

Expert:  Phil replied 10 months ago.

Hello again,

Ignore your ohm readings on the capacitor... an electronic ohm meter will not give a valid read there. Your amp reading on the S wire is below one amp, consider that a zero read.

It looks like the capacitor is bad, or the start winding in the compressor is defective.

Do the OHM tests I described earlier.

"
If the run capacitor has failed open, there will be no amperage on that wire. If there is amperage on that wire... turn the power off to the compressor, and verify that completely using a double checked voltage meter... then disconnect all 3 wires from the compressor, and use an ohm meter to test between each terminal and the compressor body...any read indicates a burnt out compressor.

 

If the compressor is not grounded, check for ohm readings between each combination of the C, S and R the read between S and R should add up to the total between C and R and C and S. All of those reads under 10 ohms

 

typically 3 ohms, 5 ohms and 8 ohms."

 

If the compressor ohms checks our as shown above, then the capacitor is bad.

replace the capacitor. take it to Grainger Industrial Supply or Johnstone Supply and have it matched up for voltage and micro farad rating.

 

The 100 amps on Run and Common are Locked rotor amps, thats normal when a compressor won't start... if it was a direct short it would blow the breaker within 1/2 to 1 second.

 

It takes 2 or 3 seconds to trip the breaker if it is just Locked rotor amps.

 

Let me know how all that goes.

 

I am currently on broadband from Antigua Guatemala where I am for a few weeks, and will check in frequently to see how you are doing...

 

As long as you rate my service to you positively, I will hold the question open with no time limits.

 

Thanks!

 

Phil

 

 

 

Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5227
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Phil and 2 other HVAC Specialists are ready to help you
Customer: replied 10 months ago.

Phil, The compressor checked out good, so I'm off to buy a capacitor. I located one for about $30 from a wholesaler. Your service has been great and I will rate you accordingly. Money well spent.

Customer: replied 10 months ago.

System up and running!


Thanks again.

Expert:  Phil replied 10 months ago.
Good work! and thanks the excellent rating. I am currently traveling in Central America, right now at the base of Travahan? volcano in Antiqua on a restaurants wifi connection.

Phil

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