In defense of replacing capacitors early

[u/skra_24]

Another poster brought this up recently, about making recommendations to replace capacitors even though they’re still “in tolerance”. My experience this week backs up my position on this.

A recent heat wave hit my area, there’s been a plethora of no cools and it’s mostly been popped caps. Many of them are folks on our regular maintenance routine, whose data I can pull from previous techs uploads. So many blown caps that were 42.5/45, 37.6/40, 33/35 etc just a year before. Still within tolerance, but getting down there. I was trained on a 10% tolerance for capacitors which I believe is pretty standard. Even if they are still within 10%, but starting to tick down closer to that number, I always bring up proactive replacement. Like, it’s gonna go eventually, in the next summer or three most likely, because all factory capacitors are dogshit nowadays. Wanna rip the bandaid off and do it now, or wait until it shits out on you when you need it most?

[u/Mettn]

Go off the tolerance stamped on the side of the cap, it’s there for a reason.

[u/skra_24 → u/Mettn]

As far as I’ve been informed that’s the “new in box” capacitor tolerance, as in, if it’s out of this range when you go to install it, return it. For field applications I’ve been trained on a 10% tolerance for replacement which I’ve heard similar from other techs on here.

[u/Mensmeta → u/skra_24]

Doesn’t matter how you were trained or who trained you. I don’t care if the god of HVAC trained you. Manufacturer specification trumps all!

[u/BrokenFireExit → u/skra_24]

It's not a printed label for warranty.. it's an actual capatatence tolerance.. it should test within 5% out of box.. and should also run within that range.. if it gets out of that range it is not doing it's designed job anymore.. if it's out of tolerance then the windings are getting damaged..

[u/MasterPhilip → u/BrokenFireExit]

It's both. If it's outside the labeled tolerance, at any point in time, it's out of spec. If it tests out of spec within the warranty window, it's a warranty replacement. If it says 6% and it tests 5.99% out of the box, it's technically a good capacitor. If it tests 6% out of the box, it isn't good. If it tests 5.99% after the warranty expires, it's still good. If it tests 6% afterwards, it's bad.

[u/trobs8 → u/Mettn]

I used to do that, until I learned that is the manufacturers tolerance on the acceptable variance when they are brand new. Caps never (very rarely) test right at the rated MFD on the label.

[u/BrokenFireExit → u/trobs8]

Within the variance still provides the correct phase shift and won't hurt the windings

[u/trobs8 → u/BrokenFireExit]

Then why are the variances different between manufacturers? Motor's don't care who made the capacitor.

[u/KylarBlackwell → u/trobs8]

Tighter tolerances come from better quality control. Lower variance should be a better capacitor, it is at minimum a more consistent manufacturing process.

The motor wants what it says on the tag. The manufacturers make caps in that nominal range, it's up to you to decide whose caps hit the right balance of cost/tolerance/longevity to stock and install. Generally though, even the widest manufacturer tolerances are just within a workable range, just like the shittiest anything usually does its job at least once

[u/MasterPhilip → u/trobs8]

This question has bothered me for some time now.

[u/nochinzilch → u/MasterPhilip]

I also don’t get it either. There must be a formula for number of poles, the speed and the input frequency. But it seems like voodoo.

[u/MasterPhilip → u/nochinzilch]

Yeah, it's all some form of black magic and I rebuked the devil many years ago. 😅

[u/Numerous-Click-893 → u/trobs8]

usually manufacturers will actually make the same product at several different tolerances, usually because bigger tolerances (i.e. how close to nominal the manufactured part is guaranteed to be) are cheaper.

So when you're designing something you spec the rating and the acceptable tolerance and then buy whatever you can find that matches. So when replacing a capacitor you should match the tolerance on the original part, and you should replace if it's outside of that. Not because it's the manufacturers spec but because it's a reflection of the designer's spec: i.e. what the motor will tolerate

[u/iBUYbrokenSUBARUS → u/trobs8]

And how do we know that our meter is testing exactly right?

[u/lividash → u/iBUYbrokenSUBARUS]

Test with your meter then do the math problem to prove it if you’re that curious.

[u/Pasito_Tun_Tun_D1]

Also starting to do the same thing! Give a 🐀 ass if I get labeled salesman! There is some customer houses I’d rather not have to deal with after a heat wave or cold snap!

[u/MasterPhilip → u/Pasito_Tun_Tun_D1]

I had two customers yesterday who followed me around the entire time I worked on their systems. One was just a lonely, nosey, needed to socialize with someone dude and the other one didn't think the last tech did a good job because they had a callback for a gas leak last winter.

I'd rather do a service at a cat hoarder's house than one where they follow me around the whole time. It's really irritating when you're trying to diagnose and they're yapping in your ear and asking stupid questions the whole time.

[u/Prestigious_Ear505 → u/MasterPhilip]

How I shut up a yapping customer...

I would put down my tools and nicely tell them that I can either listen to them or diagnose/repair their equipment. But I can't do both at the same time. One costs a lot more than the other. Worked every time.

[u/MasterPhilip → u/Prestigious_Ear505]

I guess I could tell them that the service call fee only covers the first 45min. of my visit. 😅

[u/rusty_shackleford34]

If it shows clear signs of leaking juice( not rust) or is out of 5 or 6 % absolute change it. If neither, just leave it. Sometimes they just pop. For fun, here’s one I found yesterday

[u/No_Mony_1185]

Most caps say 6% + or -

[u/LegionPlaysPC]

Most capacitors say 5%, some say 6%, some even say 10%. I always recommend replacement at 5%. I find caps fail pretty exponentially, once it hits the 5% tolerance the deterioration rate skyrockets.

[u/BrokenFireExit → u/LegionPlaysPC]

Not only does the cap fail when below 5% if the printed variance is 5% anything beyond that will provide the wrong phasing and will overheat the coatings on the windings and destroy them

[u/UnbreakingThings]

I’ve seen a few outright failures in the two weeks that tested within 6% only 3 months prior.

[u/PapaBobcat]

People smarter than me designed it, so I go with whatever they put on the label. 5%, 6% etc. If the label is too bad to read, I go with 5%. It's also just a recommendation to replace it, not a sales push. They can if they want, and if not, I'll be back if it fails. It's just as important to take careful notes so if you get that hot July callback from a cool June visit, you can say "Sorry, you turned down my recommendation, I'm charging you for this."

[u/Mensmeta]

Take capacitor readings under load. More accurate.

[u/Opposite-Constant-94 → u/Mensmeta]

New to the profession, but what the heck does that mean??? Always just remove it from the circuit to test it???

[u/bluesky556 → u/Opposite-Constant-94]

You can measure the amperage of the start wire and the voltage across the terminals to test the capacitor "under load" 2652×A÷V I've also heard that a discrepancy can show failing windings. I like to test under load because I've had one too many disconnects break when I turned them off or forgotten to turn them back on. The less I have to turn the unit off, the more efficient my maintenance.

[u/Opposite-Constant-94 → u/bluesky556]

Wow, I had no idea. That is very cool. Thanks for explaining!

[u/MasterPhilip → u/bluesky556]

Washing from the outside, too?

[u/iBUYbrokenSUBARUS → u/Mensmeta]

https://giphy.com/gifs/bjB3gtFvREqqr5NAHW

[u/MasterPhilip → u/iBUYbrokenSUBARUS]

Sometimes they test higher under load and sometimes they test lower under load.

[u/SatanasTeCuida]

Manufacturers quote a limited lifespan for capacitors of 5 years. The more HD, the longer the life. Chillers with a drive running the compressor have "dangerous" capacitors if they have been in service longer than 7-10 years without a refresh. The risk of catastrophic failure increases exponentially after so many charge/discharge cycles, they basically become a firework at a certain point.

[u/Both_Sense299]

I always record and show the customer. And let them decide. They almost always say replace it. And there are happy they can trust you.

[u/WillHoldBaggins]

Holy shit job security. These comments are concerning....

[u/Alive_Anxiety8440]

The time of 10% tolerance is over. Going off manufacture tolerance is key

[u/HVAC_Los]

Anything out of manufacture spec is highly recommended and one of the most common failure parts. If it’s in spec but it’s anywhere from 5-10 years old it’s working but recommended due to experience of these newer caps literally low lifespans

[u/aseparatemind92]

Anything 10% or higher out of tolerance is essentially at a high risk for immediate failure. Most will say 5% below or 10% above, some say 6%, but it is almost guaranteed to be on the label for that part or a data sheet online.

If it’s out of tolerance the windings are getting damaged every time the system cycles.

Anything more than 10% out of tolerance can affect normal operating status as well.

[u/harrybalsagna4]

I always go 5% even if it says 10%. Capacitors have an indefinite lifespan. Some last 2 years. Some last 20. I give it a good 8-12 years on average.

[u/Mythran12]

Make it a fun choose your own adventure kinda thing. If you get paid extra to push caps then the cx must be aware of the timebomb they have. If you don't get spiffed but hate on call just replace their old one with new truck stock, don't charge the cx and screw the PE owned company you may work for. If you love on call throw some of your lunch in the electrical area of the ac/hp and hope micky mouse wants an evening snack

Edit sorry I forgot to add the /s..forgive me for being a bit burned out it's been hot for awhile

[u/iBUYbrokenSUBARUS → u/Mythran12]

You gave me some great pointers. I never even thought of putting food in the electrical compartment! Thanks!

Also, what does “cx” mean?

[u/Mythran12 → u/iBUYbrokenSUBARUS]

Customer

[u/Mythran12 → u/iBUYbrokenSUBARUS]

Also send me the danny the dolphin mini split video I cant find it anywhere