Locked Compressors
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- čas přidán 19. 06. 2024
- Bryan teaches the Kalos technicians how to troubleshoot locked compressors in an HVAC system. He also talks about the appropriate usage of aftermarket and factory hard start kits. Although the compressor is the main focus, you can apply some of the practices to other types of motors inside an HVAC system.
A locked compressor typically draws locked rotor amps for a short period of time. The rotor rotates around the stator, and a “locked” rotor draws higher current and doesn’t spin. In those cases, the resistance (inductive reactance) is lower, resulting in a higher current. Inductive loads produce back EMF at the beginning and create inductive reactance, which is why you see higher current at the start and higher resistance later on. That differs from a resistive load in which the resistance stays fixed.
When the windings don’t have that resistance, they become hot and set off existing overload safeties. Locked compressors often overheat due to the hot windings. However, overheating may also happen due to an undercharged system, which is an operational overload. Operational overloads, including conditions that result in high compression ratios, tend to heat up the entire compressor more than the windings.
Locked rotor amps, by themselves, don’t usually produce particularly useful measurements when it comes to troubleshooting. In some cases, we might be able to stop a compressor from locking by adding a hard start kit. However, we should first verify that the capacitor is performing well, that we have sufficient incoming voltage, and that the system has been wired properly before resorting to a hard start kit.
If a new system has a locked compressor but works with a hard start kit, then we can diagnose the issue (under-voltage, long line sets, etc.). Sometimes, we can use a factory hard start kit permanently, especially if the manufacturer specifies so. In many cases, it’s better to get a factory hard start kit than rely on an aftermarket hard start kit for a long time. Aftermarket start kits are designed to work for a wide range of compressors, whereas factory hard start kits are tailored to specific systems and can take the start capacitor out of the circuit at a more appropriate time.
You may need to look at the system warranty to see if a factory hard start kit is worth adding or if an aftermarket hard start kit is good enough to keep an old unit running a bit longer. It’s worth noting that hard starts are NOT the same as soft starts, which modulate current into the compressor and produce more of a gradual startup than an immediate start with a current spike. Soft starts work well with systems that rely on generators or solar power.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
Hey Bryan! Thanks for the awesome content!
The guys at this company are lucky to have management like this.
I know right? My company doesn't do shit for training.
Agreed. I’m in the same boat. No help except channels like this😂😂
Facts, seems to good to be true.
We really are
You got that right
Always at the top of the trade! This man was born to teach! No doubt many ac technicians are better at their trade because of this man!
You’re welcome to cast me into the _much_ better lot. HVAC Time is another excellent channel. For in the field examples, there’s HVACR Videos.
Sparky here. This gentleman did an outstanding job explaining inductive reactance and locked rotor current. It’s always a pleasure to see an expert operating in their field.
Great content for this consumer, especially when you actually made the sound of the compressor locking.
Thanks. It was helpful. The most unusual situation I ran into was a rooftop packaged unit for heat and gas. It had a label stating that It was set up for 240 V AC. The unit tripped the breaker as soon as an attempt to start the unit was made. Eventually, I went to buy another compressor but in the process I learned that the compressor was supposed to have 560 V for that unit. it turned out the printed circuit board wasn’t going to let it run on the wrong voltage.
The manufacturer told me that it was not listed under any warranty. Their representative told me to red tag it and walk away. This unit was on a pizza store and they didn’t need the heat function so I disconnected that just to be safe and then I hard- wired the compressor -skipping the printed circuit board but used a solid state time delay relay and kept the low pressure cut out in the compressor control circuit.
It worked. I won’t do that again.
I’ve smacked the top of a compressor with a rubber mallet to unlock it before just to have some cooling over the weekend .. fixed orfice was clogged as well .. I pumped down what I could (the compressor was not pumping right) and recovered the rest ..cleaned the orfice .. pulled vacuum, drier, recharge ..that’s when it locked up …I smacked it a couple time fired it up and it worked but only had about 10 degree split temp
Thanks for always keeping our knowledge sharp
thanks for the content, as an HVAC student i appreciate your content. This helps consolidate what i'm learning at school.
Thank you for this type of content, I actually ran into this problem while troubleshooting a certain refrigerator but I had no clue what could have been the problem, thanks to this I now know.
Fantastic class! Thank you for the refresher!
7 years in and it’s a great reminder regarding LRA and the reasons why.
Wow!! Thank you for the video! I learned a few things I didn't know.
A good way to think of an induction single phase motor is the equivalent of a transformer with a mechanically rotating secondary. Locked rotor is like a power transformer with secondary side shorted out.
The rotor actually has the equivalent of wirings, a very low number of turns secondary (1 turn).
Internal compressor protection switch trips due to high current vs time (short time) and temperature where there is a very hot compressor. The protection switch has limited lifetime to number of high current trips, so you want to avoid tripping it as much as possible. A bad compressor internal protection switch means a compressor replacement is necessary.
A running motor induces current in the rotor that lightens load on primary side stator winding getting the motor out of LRA current region.
Most techs don't have the equipment to measure the amount of time the motor initially draws LRA current during startup but the proper start capacitor (mfd) provides a 90 degree current shift in start winding compared to run winding current. This yields the shortest start time in LRA current draw. (spins motor up quicker).
Typical startup time is about 0.4 second. If it has hard start it can last over 1-2 seconds which is enough time to pop the compressor protection breaker at LRA current. You want to shorten that time in the LRA current region.
Different compressor motors have different wire turns ratio between run and startup winding. This effects the relay required cut in and cut out voltages across start winding to disconnect start capacitor. Generally, start cap mfd is greater mfd value the larger the btu size of compressor. Too much start capacitor size can actually reduce the hard start benefit because it does not provide the proper 90 degree current phase shift to start winding which yields the greatest initial starting torque for motor.
Rough guide for start capacitor sizing.
Start Capacitors
72-86MFD - Up to 12K BTU
88-106MFD - 13-23K BTU
108-130MFD - 24-36K BTU
189-227MFD - 37-48K BTU
270-324MFD - 49-72K BTU
115VAC applications can use 250V or 330V rated start capacitors.
230VAC applications must use 330V rated start capacitors.
Another way to select hard start capacitor mfd value is 3 to 4 times the run capacitor value.
Most generic hard start kits error on the too much mfd capacitance side.
Thanks! Been “ trying” to explain this ( which makes me an idiot) to those who figure the budget for a 266 apt. Complex in the Deep South of Louisiana for a decade now. 266 units that were 12 years old when I first touched them. 12 years of hard use and abuse. Now 22 years! Those old Goodman 2 1/2 ton piston heat pumps are beasts. But now, dropping like flies. They put up with filthy coils, filters, all sorts of R-22 “ drop-in” juice without directions. 😂 Half of the outside coils are rotted from 20 + years of 100’s of dogs raising a leg on them. 🤷♂️🙄
Thank you so much for uploading this
Thanks for this very informative content
Good video Bryan
Awesome discussion which includes reasons for compressor running hot !! Just wish I could make a decision on how hot is to hot - to expensive to chase all the possible issues trying to resolve a mini fridge which is working but compressor gets very hot.
Wonderful session.. Am Helped a lot 🙏🎈
Great Lesson.
Appreciate this learning so much. Thank you
Much appreciated HVAC School
Hello Bryan, I am very thankful for you great work and educational program available to all. You and Craig Migliaccio doing great job helping us. I have question regarding three phase compressor which dose not have capacitor when it gets locked compressor what can we do to make it free again?
Thank You
Thanks for the video
Great info!
Rectorseal T05 or KS1 best fitsall I have one on my Air-conditioning. I am an Instructor for the local Apprenticeship program and Commercial HVAC technician since 1973.
Al 100% esta información gracias teacher!
Aftermarket hard starts vary quite a bit. The 2 wire (sppe) type being the lowest grade. The have a low lifespan and the relays a “light duty” to put it mildly. The 2 wire “Kickstart” are a little better with and improved relay. Personally I only use 3 wire 5-2-1 true potential relay type. They always work with Trane/Am-Standard as well. Having access to the original specs and closely matching MFD is key.
Very cool exponetion.
thanks a lot for your good Job, Keep it Up
Learn a lot....
Thanks lots of for value informations.
Great video. Thanks for posting. I bought a 5-2-1 aftermarket hard start kit but chose the option for 1-3 tons even though my unit is a 4 ton. This was based on the capacitor in the 1- 3 ton matched the specifications for the OEM hard start kit. Does the relay have internal workings that would make it much different than the OEM part?
Very interesting
good advice on doing your 'due diligence' before grabbing the hard start kit ... but one thing I might have missed - what are the next steps if the hard start kit DOESN'T start the compressor? is that the official 'death notice' of the compressor? Can anything else be done? thanks
Love these classes, lol what is the over hear to keep up continuing education like this lol
BIG ORANGE CLIMATUFF Compressor it was a beast!
Good gracias
Talking about home owner trying to do their own thing. Few weeks ago I was out for a maintenance and the system started normally about the time I showed up and in a few minutes it was making an awful noise but still running. I turn it off and start my checks figuring I would find out why. First this was a 2 ton. I look at the cap and it was a 70/7.5. Was supposed to be a 30/5. Had been that way for almost a year apparently. Told them they’ll be lucky to get much more life out of it due to their mistake.
That aftermarket hard start kit is going to work just fine. It is only active for like a second. Waste of time to go back and change it out and just more costly for the customer. Having said that I never use the two wire type they are crap. Only use the one like he shown in video with the potential relay.
Do you have any videos on variable speed compressors?
First and foremost I got to tell you are a great instructor, so you have my outmost respect. I have a question, that might sound stupid or idiotic: could a locked one third HP compressor used on a household refrigerator be fixed with a hard start kit ? Already tried the 1/3 HP electronic start device and didn't work.
Working on a Commercial Bard unit, about a 5 ton that the evap is under negative pressure. This thing leaks water and we pull the drain pan to check for leaks. It does have a P trap. I'm sure it's because of an air leak sucking air inward and pulling the water out of the pan. Do you know of a way to check for air leaks on this type of system other than feeling with your hands around it?
Tim (the tool man) Taylor says "MORE POWER!!!!!"
Hello. Can you make video how use special soft programs for to calculate the cycle of refrigeration machine?
12:09 - What's the difference between 'back EMF' and inductive reactance (that chapter - 1:51 - has a cute title, BTW, of 'inductive reactants')? Different way of looking at the same concept. The back EMF that's generated in the winding is based on the reluctance of the coil to changes in current (the inductor reacts to the constantly changing current in a sine wave by generating an opposing voltage when the magnetic Flux collapses back onto the winding )
When I got a recent compressor to start by a hard start kit , it sounded like marbles striking , shut it off and just condemned compressor , but what caused this for a 2017 condenser ?
No true vacuum pulled?
Not purging with nitro ?
I guess these couldn’t be ruled out , so I’m replacing compressor on a unit that I did not install .
Great video...thanks.
One question ...confused about soft start....if the compressor needs hard start kit for the reasons explained then would it be an issue to provide a soft start instead if the customer wanted it for the generator?
A hard start will work good at lowering starting amps but a soft start will help even more.
What about the old school way by tapping the compressor with a rubber hammer if it is locked up like they did back in the day. They also reversed the leads of the compressor to unlock it.
Awesome. raphael nyc
Great
A starter kit can be installed on three-phase scroll compressors.
I have two 34 year old r22 systems that I do not run on generator. If the power goes, we use ceiling fans and sweat. Any opinions about soft start kits with such old dogs? I hate to rock the boat and kill my compressors. Thanks
Great tutorial. Thanks
Question: let's say after all the visual testing and electrical testing is done and the problem is a locked compressor on a 2 year old system do you know another solution to start the compressor if hard start capacitor does not start the compressor ? Thanks again.
I've used the Spp hard starts by Supco, I think. There's been a couple of times when it didn't work and I "stacked" another on top, essentially twice the kick in the butt. It's worked every time but take the second one off and leave only one. If it doesn't work after installing the first the customer really has nothing to lose at that point. The alternative is a new compressor at a much higher price point.
@@bill944 Thanks for replying, i didn't know that you could stack two hard start capacitors, i tried with one and it didn't start so I went and replaced the compressor likely it was still under manufacture warranty. Thanks again
Couple of other things that can cause startup failures. Long AC power line to breaker panel and undersized wire gauge creates too much voltage drop during the startup surge current. Some outside disconnect switches use 60 amp breaker for switch which can go bad. Old AC breaker that is fine with run current, but has too much voltage drop during the 100-200 amp startup surge. Low utility line voltage is also possible.
Refrigerant overcharge can also increase startup current as well as run current. Obviously bad run capacitor is number 1 cause.
Startup surge usually last for only 0.4 to 0.5 seconds but is longer if AC voltage is low.
The compressor Klixon protection switch inside compressor trips on excessive current and/or over temp so high current trips of the cutout switch before the motor stator windings gets very hot. Multiple high current disconnects eventually destroy Klixson contacts requiring a compressor replacement if compressor has been repeatedly cycled ON and kicks off many times trying to startup. This is where the softstarter saves compressor as it protects from continuous restart attempts. Softstarter only allows one startup attempt per thermostat activation.
Once in a while the Klixon gets stuck open and a rubber mallet tap at base of compressor can knock it back into operation.
Weak link of hardstart kits is the relay reliability. I don't like using them because a relay failure is more likely to destroy compressor with start capacitor continuously connected to compressor start windings burning it out. The black electrolytic based starter cap can get very hot if left engaged too long possibly shorting out the starter capacitor. Proper start capacitor value is 3 to 4x the Run capacitor mfd value.
I thought the potential relay kicks in when voltage is low, caused by the high current draw of a stopped motor pulling the voltage down. Motor starts, voltage returns to normal, relay opens.
@@grigorshukerski4689 oh I wouldn’t say that. He’s a great teacher and business man and I wish I had him for a teacher. I don’t remember what he said in this video but he’s usually right. Maybe he’ll answer me.
18:50 Lol Good one Tyler
Inrush current has to form the magnetic field that turns the rotor, from zero charge with each startup.
Wish you guys would hire a Canadian here or there, would love the opportunity to work with such an amazing crew
You probably could. Get a working visa and move to Florida.
Move to FL We need Canadian svc techs here. Big Canadian French comunity here
You talk about on off old compressor with capacitors.How about new Inverter compressor blocked?
Hi ;
I have a question from you,
Can i ask????
💯💯💯💯
Is it true - if you multiply RLA times 4 , would it equal LRA ??
LRA divided by 5 is RLA
no.
it's different.
I've seen it as much as 8 times.
but I work on big industrial equipment.
If it's still under warranty and the system needs a band aid to continue running then the warranty should cover the band aid solution or replace the component.
Can I use the hard start kit with refrigerator locked compressors
Yes but it's called 3 in 1 for 110 volts Ref Compressor
only if u oversize it it will burn your compressor.
They make different sizes so yes
I have a compressor that was installed 6 months ago and the compressor is locked up. I put a hard start on it and it still isn't starting. Is there another way to get it running?
Reverse it how we did back in the day
Wouldn't low oil or no oil also cause compressor overheat as well?
Low oil will cause bearing failure and it will seize up just for that reason alone. Hard start kit or even a soft start would not help in that situation.
Off topic here. I'm not sure what video it came from was, a podcast or maybe a tech zoom video but I heard you talking about company policies and just personal practice things like getting enough sleep and not abusing drugs and alcohol all good stuff I was just wondering about the side work part, I must not be missing something. Like no side work with company equipment or under company names or insurances obviously but why would you stop your guys from doing side work I'm not sure I really understand. You want them fully rested and energized when they show up to work for you I get it but who gives you the control to tell them how much money they're allowed to make? I mean if an employer told me I couldn't work on the side then I would have to crunch some serious numbers and make sure that they were compensating enough to take any motivation I may have to earn extra money which in most cases I don't think employers are going to offer
I would like to attend ur classes info?
Those tiny bottle caps have worked on an old trane when then aftermarket didn't do it.
Cool shirt
Technically, I think locked rotor amps is the energy required to overcome the coefficient of friction… Resistance is just one part of the formula for determining the coefficient…
Cemf counter electromotive force is the right answer, NOT inductive reactance, inductive reactance is there locked rotor or not
Could you please repeat the students responses, we can't hear them. Thanks for your information.
You’re aging backwards. Leaner looking and more hair, lol looks good on you man!
Why not replace the compressor?
You just have to unlock em.
LRA 96 for 3 ton compressor staying for 10 second s.Most likely is Locked....
Are your guys payed for these trainings?
Serious question; I'd volunteer but it's hard to attract during off hours.
I would imagine they are. It greatly benefits the company to have educated technicians