How to troubleshoot a shorted contactor coil in the HVAC field.
Find the video on AC Blown Fuses here: https://www.youtube.com/watch?v=61YBG2e04wk&t=3s
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Find the video on AC Blown Fuses here: https://www.youtube.com/watch?v=61YBG2e04wk&t=3s
Read all the tech tips, take the quizzes
and find our handy calculators at https://www.hvacrschool.com/
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. Are you in Orleans ?
Just rewound a 3 phase contactor coil today and it works great now. Had the same shorted coil look.
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.
Such a clear, focused and practical video!
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
i know the problem MADE IN CHINA ,,,,,its everywhere in everything and its crap
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.
Good parameters for 24v coils. Expected resistance changes depending on the voltage of the coil.
Found 4 so far since March, all in carrier units
Hey Brian, just came across this YT channel. Really good stuff, thanks much.
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.
Greatest teacher ever Brian,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
Southwire has a nice set of alligator clips that slip onto the standard meter probes. I got mine at Lowes. Are you in Ottawa ?
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.
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 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.
This happened to me this afternoon. on a Carrier unit. I had to replace 3 amp fuse and outdoor 1+ contactor.
Thank you for your amazing insight and knowledge. you are very thorough in explaining every detail . thank you.
I tell you! That and many contactors are made in China!!
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.
Thanks for the video I had contactor failure cause coil last week
Starting HVAC school in September! my gush learning a lot from you
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.
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.
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.
Just was reading in one of my books. Very good that you showed the omhs . A lot of people miss that's part
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. 😆 Service area Kanata??
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. Are you in Nepean ?
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.
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…) Service area Barrhaven??
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 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.
ran into this 3 times in the past month, also alot of blower motor modules on carrier units failing lately.
Hi how i know the working discharge and suction pressures of each frions
Thanks for video
Yeah I'm curious to know what's going on myself. I've replaced like five or six contactors in the past 2 weeks.
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.
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.
My last call on Friday was a shorted contactor coil and blown transformer. Service area Nepean??
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.
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 Service area Ottawa??
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
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’m Swapping a lot on Ruuds too
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.
I was needing this video today 😞
Crazy this just happened to me yesterday. Are you in Barrhaven ?