Shorted Contactor Coils - An Emerging Issue and How to Diagnose It 

Crazy this just happened to me yesterday.

You held up the exact part in my AC. I wondered why my 3a fuse blew. Sure enough, I went and checked across the coil and got 0.9 ohm. Ordered one next day. Thank you for saving me money!

Such a clear, focused and practical video!

Thanks for this video I referred to it today lol. Im a experienced hvac technician but I always want to double check that I am doing my ohms testing right. I salute you and appreciate your pointers and teaching , it shows that you have a passion for helping others in the trade. God bless you sir and continue doing what you do it really helps and your knowledge/ clarity stick with us and its not over our head teaching.. take care talk to you soon...

Just rewound a 3 phase contactor coil today and it works great now. Had the same shorted coil look.

These examples are wonderful. This info can be very useful outside of air conditioning also. I briefly worked alongside a very experienced tech who would tell me nothing and stab you in the back. Went back working as a mechanical fitter in a factory but am still interested I learning. Thanks

Just was reading in one of my books. Very good that you showed the omhs . A lot of people miss that's part

Greatest teacher ever Brian,thank you.

Starting HVAC school in September! my gush learning a lot from you

Thanks for the video. I too have been coming across this same issue with not only Carrier equipment but Rheem and Trane as well. I’ve also noticed the capacitors that Carrier uses in they’re residential equipment are pretty cheapo as well. I find them measuring below tolerance after only a couple of years and sometimes they completely fail within 3-5 years. It’s to bad they don’t use higher quality components within the equipment especially since they cause a no cooling situation which puts doubt in the mind of the homeowner about their choice in equipment brand and contractor.

I've found a lot of these this past year.

Thank you for your amazing insight and knowledge. you are very thorough in explaining every detail . thank you.

Thanks! AC wasn’t working; this fixed it! 2013 Carrier 2 ton. In Utah, bought for $20 at Ferguson and the coil for $13. Thanks again!

Thanks for the informational content from a member of the DIY-or-DIE crowd haha One look at the low voltage schematic and a quick look confirmed this is what keeps popping 3A fuses... after going through half a bag of 50 fuses due to not finding a 'dead short' right off. Mine was tough to nail down because it would sparitacally work and kick on the unit outdoors, then go back to popping fuses after running for a few mins. I like wiring jobs in any number of other hobbies, but this hvac short has been a chore, and blatantly treated as such for the past 8mo to a year due to procrastination. Thankfully I don't live where its triple digits and can survive my lazyness. Switching to a backup wood/oil furnace over the winter is fine, but dang I wouldn't survive an afternoon in texas the temps they've had lately in some parts. I know some folks down there and all I say is I hope they keep and enjoy all that as much as I enjoy the cold weather haha

Good video, thanks. I had this same thing happen two weeks ago...blow fuse and low ohms (2) across the contactor coil. New coil was 14 ohms. Once replaced, unit was fine.

I went to a no cooling call yesterday in a house with 2 carrier systems. Both systems were down with blown fuses and BOTH were caused by a shorted contactor. Only 2 years old too

I have seen this in a Trane A/C this week as well that was installed last year. It was a Homer branded contactor.

Hey Brian, just came across this YT channel. Really good stuff, thanks much.

Thanks for the. video!I replaced my 10+ year old contractor abut two weeks ago along with my capacitor. Got home from work yesterday to a completely dead system, blown 3 amp fuse on the board. s soon as I opened the service panel outside I could smell the shorted coil. old coil read 14-20, the new one on the unit was at 0.7. got a replacement down the street on a Saturday lol, sweet fix.

ran into this 3 times in the past month, also alot of blower motor modules on carrier units failing lately.

This happened at my house yesterday. No power to thermostat. Wires looked okay, air handler looked burnt up, ohmed out at 3.7 ohms. Thanks for the info hvac school.

The couple I've taken apart, Packard and Dayton, have rectangular steel plate that is pulled down on to the E laminations. Same as the electromagnet in a toaster holds a plate keeping the toast down till the time runs out. The contactor you showed at the end of the video has another E profile mating to the removable E laminations to coil fits into. I could see how a fitting problem could creep into the manufacturing since those 3 surfaces have to mate flush. If an air gap remained, there would be higher currents since the reactance would be less. Like if you only partially inserted the core into a solenoid. Higher currents, more heat, eventually you see insulation failure near the center of the coil.

Thanks for the video I had contactor failure cause coil last week

I ran into this issue last summer with 2 different contactors. The first one the Furnace Control Board was not fused and this issue fried the transformer. It took awhile for me to isolate because I've never run into it before. The 2nd time it happened, I knew right where to go.

emerging problem - interesting. reading 0.00 across low voltage on my contactor and couldn't find many videos addressing this. thanks!

Pure Quality. Thank You.

Have seen this off and on for thirty years. Every great once in a while until about 2005 . It slowly increased until it is fairly common nowadays.

Good explanation 👍

I was needing this video today 😞

GREAT JOB SIR

Thanks for sharing

This just happened to my Bryant installed in late 2018. Same symptom of a blown fuse when the thermostat calls for cooling. Tested all the wires to rule out a thermostat or some other short. The 24v terminals on the contactor had zero resistance. Took the cover off the back of the contactor and the coil looked and smelled burned. It looked just like the coil at 5:55 in this video. This should not happen on a system that is less than 4 years old. Cheap parts. Thanks for the video!

We shouldn’t be surprised that more and more failures are occurring . Just like everything else in this world, the goal of manufacturers is “ make it cheaper”. That attitude is what keeps us busy.

Southwire has a nice set of alligator clips that slip onto the standard meter probes. I got mine at Lowes.

Had this multiple times this year but came across something interesting with a single pole contactor on a call yesterday. Door switch on furnace blown, transformer blown. Replace both, blower turns on no led on board. Smell the transformer right away. Check voltage at board and had 7 volts between R and C. Electrical shunt? Replace the contactor fixed all issues

Good parameters for 24v coils. Expected resistance changes depending on the voltage of the coil.

My Carrier installed in 2019 just quit two days ago and kept blowing fuses when the AC tried to kick on. Took a while to figure out where the issue was, but after physically depressing the contactor button and seeing the fan at the condenser spin up, I was pretty sure I found the problem. Then I watch this video and sure enough it’s talking about shorted contactors in 2019 Carriers. Good stuff. Not a tech, but as a homeowner who likes to fix stuff myself, content like this is valuable.

Thank you

Hello teacher. Thank you

Ive had a lot of those Homer brand contactors shorting out.. had one last week on a 2 yr old American standard , and many more on Carriers

Nice job and video like always

Very informative

Hi Brian, Thanks for the update on a Field Related Problem you are seeing. It helps us all !!! But, I Have a brand New 3 Pole Contactor ( 24 volt coil ) on my Table That Measures 1 Ohm resistance across the coil. I’ll double check it. But, You Might want to make a updated video that states Less than 6 ohms is not ALLWAYS A Shorted coil. Depends on Voltage , size of contactor , manufacturer etc. a Good reference is just grab a New Coil off the truck and it ohm it to make a reference. Just a FYI.

Good video

Just replaced the contactor on my 2018 Goodman ARUF447D14AC air handler. One of the electric heat contactor coils was reading 2 ohms and not shorted to ground, now aux heat is working properly

8 ohms will blow a 3 amp fuse eventually. 24v /8= 3 amp. (Border line) Ohms law. I agree stick to 10 to 20 ohms. We have allot of 3 amps in some units out here. A 5 would hold better but stick to 10 to 20 ohms definitely. Great video I learned it the hard way

I've seen contactors with 30-60 ohms that were popping low volt fuses/breakers. Is there a page/sheet for ohms needed for relay/contactor coils? I'd love to have that on hand to know. I've ran into this problem a few times, my first instinct is to replace the contactor if I find no direct shorts on low volt wires. Awesome vid bro

Found 4 so far since March, all in carrier units

This helps, I've just been swapping with a new contactor to check if the old one is bad, this will save me some time for sure. The issue I ran into recently that I did this with was a 2014 Carrier Infinity system, the contactor was good. The issue I was having is that the system was a 2 stage compressor (single compressor) but couldn't start in FIRST stage, only second. So the contactor would pull in for a second, then fail; it had 2 contactors, one for each stage, and the second stage contactor was pulling in and running at second stage to satisfy the thermostat, but would lock out when it tried to go back to first stage. The Board has an indicator light for second stage, two blinks, then a pause, which it was doing, then when it tried to go to first stage it would give me the error code for "failure to reach high stage"; which is odd. I learned there is two wires, vr and vf which prove to the board it has enough voltage to run that stage, and that is what will throw the error codes. I didn't have a Megger (which I bought after this run-in) but I deduced that the compressor windings were beginning to break down, so the compressor could only run in second stage. Thanks for the video

I’ve had a bunch this week on Goodman’s. Keep finding them to have five ohms when they have twenty off the truck.

This happened to me this afternoon. on a Carrier unit. I had to replace 3 amp fuse and outdoor 1+ contactor.

My last call on Friday was a shorted contactor coil and blown transformer.

I've been seeing this in some trane air handlers I service. They use contactors instead of sequencers. I would like to recommend a video. Go over boiler zone valve controls. How to wire them, th-tr, tr, th. How the end switch side works.

Hi how i know the working discharge and suction pressures of each frions Thanks for video

Great video...im saving it.

I’m Swapping a lot on Ruuds too

Carrier is known to have issues of short lifespan of this contacts, at times no fuse is blown but the step down transformer burnt. In cases they damage the board before the fuse go out.

There’s a video where Bryan and his brother are testing a multi speed motor on a table ... I remember watching it and not getting so much out of it. I’ve been looking for this video because I get what they were trying to figure out. Anyone seen this video? Or was it a podcast and I did a good job imagining it.

Had one Thursday

I changed out a contactor a few weeks ago where the contacts very very burnt and pitted, but the coil itself ohm’d out just fine. 😆

just had one do that

Had a 2019 contacter fail this week

Curious what the unloaded control voltage is. If Carrier is using cheap transformers you may have 30 volts before a call for cooling. High voltage hitting the coil every cycle will damage the coils. Worth a shot to check on the next one... This was an issue with 24volt gas valves failing in the late 90's.

I have had 3 no cool and heat calls because of this, most showing continuity to ground on my Y wire and i chased it back to the outdoor unit. However today i was thrown for a loop when the new contactor showed continuity to ground on the Y in to the contactor when i had it wired in? Wires were disconnected in the air handler/furnace. Is it normal to have continuity to ground on the 24 volt in on the contactor? New tech here

i got 120 volt contactors on the ahus in my building and im having issues with chattering... all wires are solid connections no corrosion and no low voltage im assuming the coil is bad on it.. funny part is it will fire the motor up if you give it a knock or two... and run for a hr or so and ill find it tripped at reset relay again

What about 3 pole contactors? Does the same apply for those as well? A new one out of box measures lower then the 2 pole.

This happened to both of my Bryant systems that were just two years new. They should have a recall on these defective made in China part!

Thank you for sharing, I was unaware this was happening on newer units. I am assuming since these are under warranty the distributor are going to give us the the same low quality contactor until their inventory is depleted. Does anybody recommend any brand for the reliability? I have had a couple issues with Jard and Packard brands in the past

Is the black stuff on the copper a clear indicator that the coil is bad

Found one yesterday

I'm a newer tech and I'm seeing this almost once a week. Maybe I'm unlucky. Been seeing it in newer Carrier and Rheem units.

Have u heard of a code 73 on a carrier 24ana

QUESTION: if my original contactor (off a 2019 Rheem) was a Zettler single pole 24V coil (FLA 25 LRA 150 RES 35) what would. Good "upgrade" contactor be?

Yeah I'm curious to know what's going on myself. I've replaced like five or six contactors in the past 2 weeks.

I wonder if you could put a 2 amp fuse in series with the contractor coil to protect the rest of the AC circuit from going dead if the coil shorts out? At least your blower fan would still work.

Name of Brand for those leads?

If the coil is bad can the contactor still pull in intermittently? Or once the coil reads low ohms its done.

is it possible to buy replacement coil online

Say you want to trigger that switch artificially to test it live. What would be the easiest way?

Can a bad coil cause a contactor to engage and close a circuit, but fail to disengage when given a signal by the electronics, causing it to keep a closed circuit until physically switched off?

Just to add. Not all shorted contactors will cause the fuse to blow or a burnt transformer. I've had the majority just cause the unit to not run or maybe what I call scramble the t-stat until the contactor is replaced. I've had new tecks take hours trying to troubleshoot the issue until they either do a head slap and find it or call me and I tell them what to look for on the contactors.

I've found new contractors with one side of the coil not connected to the terminal.

I seen this with a match up we use with carrier and nest thermostat. Gives me error code of your signal lost. As soon as I replace contractor fixes issue.

The sealed coils seem to fail more

My guess is this is a result of reverse EMF produced by the quick collapse of the magnetic field. I wonder if the addition of a diode would correct the problem.

I have one shorted to ground. Yep and a blown fuse. Yes it's a carrier and yes it's Chinese!! I'm surprised !!!

It's really hard to claim any coil < 6 ohm is failed coil. Usually you can go by elimination, testing directly the contactor, or insulation test ( during that test many processes are involved according to type of coil, etc...)

I spent 50 years as a commercial electrician and NEVER came across a shorted coil. They bad coils were always open and never blow a fuse. Worked on coils from 12 to 480 volts mostly AC. When I opened a coil it might havs a black burnt spot where it arched when the voil opened up. Junk original equipment that manufactures install are garbage. If it was important or ran 24/7 would install a Square D or an Allen Bradley next bigger size starter.

So for the coil we want high resistance and if it’s low it’s shorted and for the path of current we want 0 to low resistance.

Wow just checked from blowing fuse, coil was 1.2 ohms😮

Brain, You missed a part. You said this is happening in Carrier units. You should have touched on the transformer. If you only have 208v coming in and the transformer is set to 240 from factory. Your low voltage is going to be lower. This will cause the coil to have higher amperage. More heat will short a coil.

Lesson learned. The top 🎩 switch should read 0 ohms. The coil should have between 12-20 ohms. I recently tested my coil at home and had 14ohms.

I have found bugs fried inside where the contacts are made, also the contacts are just fried together and won’t open. Ants invested the contactor and made it stop working.

i am willing to bet that the manufacturers are starting to make the coils as 12 volt coils and over volting them to 24 volt. why? possibly copper prices have gone up in recent months and they are using half the amount of wire to save on costs to keep the contactor/relay at the same consumer price. to verify this theory tear down an old contactor coil and string it out and do the same for a modern one i am willing to bet the modern coil is half the length. they could just replace the power supply for the "y" circuit but the problem is not everyone replaces the entire system they may only replace the indoor unit or even just the control board and power supply and then it would not be enough to power the contactor. another possibility is for the manufacturer to use a resistor of the value of half the length of the coil to compensate for the missing length. one final way is to use aluminum or steel wire instead of copper as aluminum and steel is cheaper. at the scrap yard you get paid $2 to 3 per pound for number 2 copper. maybe you get 75 cents for the best aluminum scrap. steel or tin goes for 1 to 10 cents a pound and is paid by the 100 pound usually though some scrap yards will have a scale set up for smaller amounts of tin to accomodate those riding bikes pulling very small amounts of scrap.

Why do some supply houses list that part as a "Contactor Relay"? Is it also a relay? Example... ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-y4sx84SHMlw.html

Everything is failing on carrier

TTThhhaaannnkkk yyyooouuu!

Just ran a call on a 30 year old unit 😂 thing is performing better than most units manufactured in the past 10 years. Why is that? "Made in China" perhaps.....

should just go ahead and have that calm down drink before the video, the alcoholic had shaking is nauseating and made those close up hand shots maddening to follow. geezus man

Made in China