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Juggular

Capacitor in AC

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My central air died.  

The AC gets power just fine.  But it was not on.  The radiator was not hot.  It made a small buzzing sound as if the fan got stuck.  So I got a brittle twig and moved the fan, just to see if that would get it moving.  The fan rotated easily back and forth as I pushed it. But it did not engage.   

I heard a buzz inside, near one corner where there was a gigantic capacitor.  I thought, "I know what capacitor does! You hook it up to your ESC!"   

I cut the power at the breaker.  I pulled out the disconnect thingy on the outside.  It had absolutely no power.  But the buzz continued.  Why would it buzz if there is no power?  "Ah, the capacitor's job is to store power. Maybe that's why?"  Besides, both the fan motor and the condenser motor didn't work, and the capacitor is connected to both.  

So I ordered a new 80/5 capacitor (same as this thing below).  Until it arrives, does anyone know if a faulty capacitor buzzes?  The only other thing that could make the buzzing noise would be the condenser motor. (But if that got stuck, wouldn't the fan motor be still working?) 

wpojaKs.jpg

If the new capacitor doesn't work, I would replace the contactor thingy next (red arrow above). 

Or should I replace contactor as well? 

It worked fine the other day.  It wasn't used for 7-8 years because we used window units.  Maybe the sudden jolt wasn't good for the 30 year old capacitor.  I'll get the new one in a couple of days and I'll swap it.  Fan is the brown wire, Herm is blue, C is yellow, I think. 

If I'm totally wrong about this, please let me know.  

P.S. I'm trying to get an RC car out of this. (Every time I fix something, I get some credit from the woman who thinks I asked her to control my wallet. The only thing I said was "I do." I never said, "you do.")  

 

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If you have shut down the breaker at the electrical panel and pulled the exterior disconnect out of its socket, and you are still getting some buzzing at the unit, I would be super-careful about an electrical fault somewhere before touching anything.  Nothing in that unit should be energized or buzzing when all power is cut off.  Use a meter to confirm nothing has power on it before touching it.  (Edit:  Did you shut off the breaker for the inside unit as well?  The controller in the inside unit controls the contactor in the outside unit...)

The capacitor is used for starting the motors; certain types of motors have an additional winding in them that "lead" the other main windings a little bit.  When power is first applied to the motors, the capacitor provides power to the lead winding slightly in advance of the main windings so the motor has a direction to turn.  These motors are different from the brushed/brushless motors used in our RC cars.  A good explanation:  https://eepower.com/capacitor-guide/applications/motor-starting-capacitor/#

The contactor assembly that you highlighted in red can be opened, and the contacts can be inspected.  I had one of these units semi-weld the contacts together due to old age, so it had to be replaced.  The outside unit was running all the time even though the inside thermostat wasn't calling for any cooling, so as a result the coils inside the attic air handler froze.  The system expects house airflow to add heat into those coils; when it's not there, there's nothing stopping the coils from freezing.  The other possibility is that your contactor is corroded and won't switch power on at all, in which case your house will circulate air but the outside compressor won't run.

Most importantly, be absolutely sure the power is completely absent before touching anything!!!  Use a meter to check it all!  (Edit:  Power to both the inside unit and outside units should be off!)

If your contactor looks good and you replace the starter capacitor and there's still no success, but you hear buzzing coming from the compressor motor itself, it's likely the compressor is frozen and then you're looking at replacement.  In my case my whole system was 20 years old, so it was time to just replace everything indoor and outside.  It was thousands of dollars at that point to replace the system.

The other concern you might have since you haven't used the system in 8 years is the re****erant level could be low.  I imagine the system is probably even older than 8 years.  Average consumers/citizens can't get access to the ozone-affecting re****erant needed to charge the system; you have to be a licensed HVAC person to handle that material.

I hope your contactor is good, a new capacitor works, and you have sufficient re****erant!  Otherwise there is not much else you can do and it will likely be a service call since the technician will have additional gauges and re****erant on hand. 

The joys of troubleshooting and repair...

 

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Wow, Thank you , @speedy_w_beans!  

That was a lot to learn!  Yes, I disconnected the inside breaker.  And I went outside and disconnected the disconnect in the metal box.   I installed a new disconnect last month.  Oddly, there was no ground wire from the house. Maybe the previous electrician grounded the copper pipe for the coolant somewhere in the house.  Even so, I connected a piece of wire directly to the ground.  (only about 2 feet into the packed, often wet dirt though. I have a 4 feet copper peg for lightning rod ground. But I didn't use it because that seemed like an overkill.)  

 qgGyYdB.jpg 

No voltage showing on the pen-shaped voltage detector. So the AC wasn't overloaded with built up electricity or anything.  

When it worked, the AC sucked in all the moisture in the house like crazy.  68% relative humidity would be down to 35% in little more than an hour.  So I know the inside unit was cold as ice.  Who knows, the copper pipes could have sprung a leak after few days of use since it wasn't used for a long while.  If something leaked, I'll call around. 

I hate calling around.  Every time I call, they'll always say to replace the whole thing.  Last time, it was the fan control circuit board on the furnace.  All I needed was the circuit board. Instead of fixing that, they were like "what are you going to do, keep on using the furnace until it hits 30 years?"  Yes, I have. The efficiency is still 91%, and the two carbon monoxide detectors I installed here and there never went off.  

But if the compressor was gone like yours was, then I guess the whole system has to be replaced?  This AC is almost 30 years old so I'm expecting that the copper lines for the coolant might not be good, even if I replace the AC unit itself.  But if it dies, I might knock off a brick and install a $900 ductless split thing just for the kitchen. That might be easier than re-laying all the coolant lines into the duct.  (Usually my wife is the one who wants to save money, but for this, she says she's fine replacing the whole AC. So we could go either way.)

I sure do appreciate your input. I know better where this is heading now.  

EDIT:  This arrived today, and it works now!  Like magic!!  Thank you again.  Hopefully the AC would last a couple more years...

Dj0wpAI.jpg

 

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GJ, Juggular!  I wouldn't know where to start besides calling my guy..lol.   I have a contractor that does everything from plumbing to HVAC and this year I had them replace a contactor (?) thingie just in the vicinity of your capacitor.  My unit is 8 yrs old and per the contractor, has many years of life left.

I am on their 3yr seasonal program so they come out once in the Spring (AC checkup and cleaning) and once in the Fall (heater core cleaning and check) at a discounted rate.  

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44 minutes ago, Willy iine said:

I had them replace a contactor (?) thingie just in the vicinity of your capacitor.  

The breaker tripped last night, so I've ordered the contactor thing too. 

I'm hoping that could extend the life.  At this point, I know I'm stretching it.  But a capacitor + contactor is less than $80.  It's worth the shot.  The SEER rating is 12. (Under 13 is not allowed to be sold anymore)  But I run it after I air out the house at night.  Night air is cooler, so I get free cooling.  After that, cooler air is easier on the wimpy AC too.   

29 minutes ago, martinjpayne said:

@Juggular well done with the fault finding... now, what new RC car are you going to buy with the money you saved?

Thank you.  I don't miss a beat when it comes to buying Tamiya!  It already arrived. (If I wait too long, my wife would forget what I fixed, so I had to move fast)  

p7XlOYp.jpg

The electrician quoted $225 for the disconnect that I installed myself.  MF-01X was only about $130, so I ordered a Toyota FJ Landcruiser shell and a static kit too!  Rest assured, I intend to milk the capacitor and contactor to the fullest extent as well.  

T2WFvob.jpg

 

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On 7/16/2021 at 3:31 PM, Juggular said:

EDIT:  This arrived today, and it works now!  Like magic!!  Thank you again.  Hopefully the AC would last a couple more years...

Dj0wpAI.jpg

 

2 hours ago, Juggular said:

The breaker tripped last night, so I've ordered the contactor thing too.

 

Glad to hear the capacitor got things running again!

If your compressor kicks on and off correctly per the thermostat's demand, then the contactor may not be necessary.  The main ways a contactor could fail include:

1) The control input to the contactor's main coil doesn't work anymore, so the circuit stays open and the compressor doesn't run any more.  The breaker wouldn't/shouldn't trip in this case since there's no major demand for power from your electrical panel.

2)  The control input to the contactor is working, but the contacts themselves are shot and you're not getting power to the compressor.  The breaker shouldn't trip with no power demand, although I'm not sure what would happen if only one of the two contacts was shot / open circuit.  For sure the motor would look like an imbalanced load to the breaker/panel.

3)  The control input to the contactor is working, but the contacts welded themselves together and now the compressor runs all the time even if the house is cool enough.  The breaker shouldn't trip even if the compressor runs continuously, but the coils in your inside air handler / furnace will likely freeze over.

If the breaker in your electrical panel is as old as the house and/or air conditioning unit, you might have a breaker that is getting weak.  I have a circuit in my garage that can't reliably handle my air compressor even though the motor for the compressor is under the rating of the breaker.  It seems to be a related to the initial transient or power surge when the motor first kicks on.  I've jiggled the breaker off and on a few times and it will work, but sometimes the compressor pops the breaker unpredictably.  I chalk it up to the inrush current of starting the motor combined with the 30-year old breaker in the panel.  I should really get off my dupa and replace it.  Explanation:  https://everythingwhat.com/can-a-circuit-breaker-become-weak

 

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27 minutes ago, speedy_w_beans said:

If the breaker in your electrical panel is as old as the house and/or air conditioning unit, you might have a breaker that is getting weak. 

That cannot be!  The panel is only 59 years old!  :o  lol... the house is old... we have the breaker panel from the 60's.  

Thank you, @speedy_w_beans!  I think I might return the contactor and use that money for more productive things like RC tires.  

I can see that replacing the breaker wouldn't be difficult, but I'm too scared of that.  It's not like I can stop in the middle and live like nothing happened.  Even though that upgrade might earn me a couple of Bruisers, I think I'll ask a professional to handle it.  

 

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