Bryan teaches the Kalos techs all about capacitors, including how they look on diagrams, why they fail, and how to handle them on service calls. He also gets some capacitor and hard start kit myths busted.
Even though we may imagine that current travels across the capacitor, the electrons DON’T travel through the capacitor. Capacitors don’t “boost” voltage or current, either; the microfarad rating is actually more likely to reduce or restrict the amount of current that travels through the start winding.
It may be helpful to view the capacitor as a balloon or membrane that stores and releases electricity. As the voltage changes via alternating current (60 times per second for 60 Hz, 50 times per second for 50 Hz), we measure its average via the root mean square (RMS). So, the capacitor charges (through the start winding) and discharges 60 times per second from the same way it came. Capacitors have attractive forces due to the high surface area between the two plates; there is a large sheet of plastic with metal rolled into the capacitor.
You can also think of a capacitor as a third hand to help spin a motor; when we spin wheels with our hands, we apply directional force instead of horizontal force. The legs of power act kind of like sources of horizontal forces, and the capacitor acts like a hand to begin spinning the motor.
Three-phase equipment and ECMs don’t require a capacitor because there are already three “hands” spinning the motor without help. On single-phase equipment, the start winding always has current running through it, not just on startup, even though we need another “hand” to help start the motor. That’s why we have run capacitors.
If the run capacitor is too small, the compressor might not start and will get hotter because the run capacitor generates heat in the run winding (not the start winding). When the rotor stays locked for any reason, including an undersized capacitor, the amp draw stays high until the compressor goes out on thermal overload. If the run capacitor completely fails, nothing happens on the start winding; no current moves through it whatsoever. A failed start winding may happen if the capacitor is wired in incorrectly, if the capacitor is too large, or if the hard start kit presents problems. So, be sure to do a thorough visual inspection of the capacitor and any other accessories.
We need to be careful when using hard start kits; they don’t add a phase shift but give us more current to hit the start winding. However, the start winding isn’t designed to handle full current all the time; the hard start kit needs to be able to shut off or take itself out of the circuit, usually via a potential relay. The best hard start kit is almost always the OEM hard start kit, but aftermarket kits are acceptable for temporary solutions or when the unit lacks a factory recommendation. It’s also worth noting that capacitors can indeed weaken over time without failing completely.
Incorrect capacitor sizing is common, especially after capacitor or compressor replacements. Sometimes, technicians accidentally install a new run capacitor of the wrong size. In other cases, a new compressor may require a different capacitor size than the previous one; we can’t just assume that the new compressor will have the exact same requirements as the previous one.
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Thanks for the video just in time for cooling season here in the Midwest. Learned a lot here!
I am a EE , and I am trying to learn HVAC .
So if they don't store power. why is it that you can sometimes short across the terminals and get a loud pop?
Would it hurt to install a 5mf where it originally had a 4mf?
So tedious.
Bryan you are an excellent instructor. Fascinating learning from you. Thank you.
Great video and explanation. A capacitor in this application acts much the same as an accumulator in hydraulics, or a pressure tank in plumbing. All of these items can release a lot of energy(pressure/volume) fast, when needed. Cheers.
My start capacitor went from lasting for a decade to going bad 5 times in the last 4 years. When it died a week ago, we tried using a hard start. Should this hard start last longer than the start capacitors that kept dying?
You have HVAC guys installing hard Start kits on Brand new systems to up-sell customers because they think the compressor sound funny… crazy techs..
“Or heaven forbid if they’re an electrical engineer” 😂
the light bulb went on when you explained how the electrons flow threw the cap at 25:00
Great video. I installed a 5-2-1 start kit on my 4 ton unit. It is properly sized (3.5 to 5 ton) for the unit. You have me a little worried about not using the factory kit. Unit is 20 yrs old and has been running great. Should I be worried?
Excellent 👍👍
Hi, does the capacitor also correcting the motor power factor? Thanks
"my husband is an electrical engineer he installed it himself"
Great video! I have no formal education on A/C and I have not been able to get a good understanding of capacitors from my licensed A/C technicians. I am installing a 10k 30amp generator and would like to know if a soft start is any better than a hard start. I was looking at a soft start from Micro Air which is almost $400 and I'm wondering if it is better for the unit than a hard start. Any comments is appreciated. Thx
this guy is struggling.. he needs to exercise… the whole time he is gulping and breathing hard and struggling just to be alive.. its not that he is extremely overweight but he is a fat guy in a normal sized body and he is totally struggling and unhealthy.. dude you need a good treadmill or to run a couple miles a night … because your compressor is flooding… sorry to say this but its apparent and distracting and no one else is going to tell you.
I had a 3750 sqft home (Chicago suburb) with 2 furnaces and 2 central air units. The Rheem condensers were 3 ton & 2 1/2 ton. Walking past the condensers I noticed one of the units was hummimg but not running. I took a rubber hammer and tapped the side of the case and the unit started running (I did this twice in 2 weeks). The units were 10 years old ( I bought the home new and these were installed new). Having a lot of experiences with oil filled motors, I knew there might be a bearing wear issue and when the unit stopped in the wrong place it would not start. I installed a hard start kit that I got with a bunch of electrical parts from a friend. Four years later I sold my home and it was still working, units were 14 years old. The furnaces were Bryant 90 plus and one did need a repair in that same year, but it was only a relay and sensing element. No other problems in the 14 years on those units. Thanks….Jim
PS….my current new ranch home has a Trane 80 plus furnace (builder sub installed) and a York a/c system with condenser (a licensed friend & I installed) running 19 years without any problems or repairs.
that's a polarized cap
‐‐‐l l‐‐‐ is a cap
that's not the symbol for a cap
Do you get higher voltages across the capacitor due to back emf ?? Have you a video explaining this.. I found this video great.
Outstanding class! very informative and I learned a lot!
How does this compare to a soft start kit?? Thank you
Why doesn’t the A/C unit need a potential relay when all refrigeration compressors that I know of do? Good video.
This video is really helpful.
thank you so much🙏
Also, a weak capacitor is a failed capacitor if it's too weak to do its job. There is no in between.
Cool video. However, the power from the electric pole does not have a phase. Power is simply power. Phase has to do with the mechanical tool.
Current wave leads the voltage wave. Split phase. Why not teach that?
I am old school. If 1985 is old school.🤓
These poor guys. Good luck.
It bothers me more than it should that the picture of a motor that pops up, whenever a PSC motor is mentioned, isn't actually a PSC motor!🤣
Thank you…very informative.
DMB for life!