Compressor not turning on? Loud clicking, heavy power draw

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  #1  
Old 06-09-19, 03:36 PM
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Compressor not turning on? Loud clicking, heavy power draw

Hi all!

My AC isn't working at home and started investigating. I've done some tests and think it could be either capacitor, compressor, or potentially wiring, but you all my have some better ideas!

Fan is working and air is blowing, but air isn't cool. The compressor seems to make a loud clicking sound when trying to turn on, I recorded it here: https://www.youtube.com/watch?v=pw-t...ature=youtu.be
Inside, I hear a buzzing at the AC breaker for almost 2 seconds and the lights in my place dim, so must be drawing a lot of current.

I have an outdoor Carrier 25HCE448A300 unit. Capacitor is HC98KA071. Defrost control board HK32EA007. Compressor is LG ABG042KAC. Refrigerant accumulator KH71KN163-B. Indoor furnace FV4BNF005. Furnace PCB is HK61EA005.
  • outdoor fan is working
  • tested capacitance between C/HERM and C/FAN on capacitor, they are both close to rating
  • none of capacitor contacts are shorted to ground (capacitor casing)
  • ohmmeter shows an initial spike between C/HERM and C/FAN, then goes to 0 ohm -- however, I found that if I leave the ohmmeter sitting on the capacitor electrodes, it will start to show a megaohm resistance -- if I short the leads together then retest, the capacitor appears fine and does its initial spike and back to 0 ohms
  • no bloating/cracks/etc on capacitor, visually looks good
  • contactor is working
  • relays on PCB are working
  • 24VAC output is getting to the outdoor unit
  • visual inspection of defrost control board is good (I removed it and inspected everything under microscope including each component, and tested many components as well)
Any thoughts of other things to test or what the potential issues could be?

Thanks!
Samy
 
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  #2  
Old 06-09-19, 03:42 PM
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And to clarify, 240VAC is coming out on the main power, and 24VAC is on the signal lines from thermostat.
 
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Old 06-09-19, 03:59 PM
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ohm out the compressor windings: https://www.lennoxpros.com/news/the-...ase-compressor

Bad start or run winding will cause it to not start but draw a lot of current trying to start, then trip the overload.

if you have no resistance between common (c) and start (s) and common (c) and run but have between start and run the windings are fine but the thermal overload is open.

start to run should equal resistance of the sum of start to common and run to common.

If the windings are good, you can try a very cheap 2-wire hard start kit, example: https://www.supco.com/web/supco_live...&subcategory=5

If it starts with it, may want to invest in a more proper hard start kit.

If it doesn't start with a hard start kit, the compressor is bad.

In video sounds like it's mechanically damaged- normally when a compressor fails to turn over it just hums until the overload trips.
 
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Old 06-09-19, 06:39 PM
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Thank you @user 10! I will try your steps and report back.
 
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Old 06-09-19, 07:15 PM
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Run-Common 0.8Ohm
Start-Common 0.8Ohm
Run-Start 1.6Ohm
None of these were shorted to ground. I guess hard start kit is next thing to try?

I read somewhere that Start-Common should be 3-5x higher than Run-Common -- does that matter here?
 
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Old 06-10-19, 11:08 AM
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I don't remember what the specific resistances should be, but the start and run should be different.

It's possible there's some issue with the windings.

You can measure from the wires to make sure it's not a wire/terminal issue cause the compressor not to start.

Generally, if the unit is 10 years old or less compressor may be under warranty if it's bad, but doesn't cover labour.

I wouldn't have a compressor replaced in anything more than 12 years old, as you're looking at half the cost of a new machine for something with a 15 to 25 year lifespan.
 
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Old 06-10-19, 06:37 PM
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Run-Common = 0.8Ohm
Start-Common = 0.8Ohm
Run-Start = 1.6Ohm


Your run to common looks good. Your start to common looks too low. Start should be higher (more) resistance than the run winding. It may indicate a burned start winding.
 
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Old 06-11-19, 12:43 PM
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an el-cheapo superboost is under $20, give it a try even if a bad start winding is suspected.
 
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Old 06-12-19, 07:58 AM
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Okay, will try that, thanks. I have a new capacitor I'm going to test first, then will try that if no luck.
 
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Old 06-12-19, 02:53 PM
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FYI, I put in a new capacitor and same issue. I'll get a superboost and try that and report back.

Thanks again! If the superboost doesn't solve it, can I actually open the compressor to replace the potentially bad coil or is it not operable?
 
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Old 06-12-19, 05:00 PM
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Compressor is sealed and not serviceable.
The shell is also holding back the refrigerant charge.
 
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Old 06-12-19, 06:05 PM
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you'll need to have the compressor changed if not the entire a/c.

only makes sense to change the compressor if the unit is a good shape and has many years left.
 
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Old 06-17-19, 10:24 AM
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Okay, so I've added the Supco SPP6 super boost.

Now when everything kicks on, there's no weird noises at the compressor, no more buzzing on startup at the breaker panel, and no more lights dimming on startup. I'm not sure what the compressor should sound like so it was hard to tell whether it's "on" with the noise of the fan above it.

Heat works now! It wasn't working before.

Unfortunately, cooling still has only very mildly cool air (might be room temperature as temp of the place is not changing). It's a heat pump system.

Thanks for all your help thus far. Any suggestions at this point? The outdoor compressor unit is only 3 years old so would be a shame to have to replace it.
 
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Old 06-17-19, 06:22 PM
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You can tell if the compressor motor is running with a clamp ammeter.

If the amp draw is very low or above the rating, odds are you have a mechanical failure.

Need gauges put on to know exactly what its doing - need license to do that and against the rules on this board to give any info on pressures.

Normally compressor makes a distinct low to medium pitch noise, louder than the fan.



Heat works now! It wasn't working before.
its probably just running on aux heat.

The outdoor compressor unit is only 3 years old so would be a shame to have to replace it.
compressor should be under warranty if its bad.
 
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Old 06-23-19, 01:52 PM
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Hi all & user 10,

The SPP6 actually resolved it! The heat was due to my mis-wiring on Nest (I had also just replaced my thermostat) and I moved Y (which is also O/B) to Y on the Nest rather than O/B (for my heat pump).

Thank you!
 
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Old 06-23-19, 02:18 PM
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You weren't energizing the reversing valve when it needed to be for cooling.

You can feels the large copper line at the back of the condenser.
It should be ice cold when the condenser is running in cooling mode.
 
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