HVAC Training Board: How To Troubleshoot A Transformer (How To Check A HVAC Step Down Transformer)
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Published 2022-01-02
How To Test A HVAC Step Down Transformer
Electrical Transformer Testing
How To Check A Transformer With A Multimeter
How to test/check a hvac transformer?
How to test/check a step down transformer?
How to test/check a isolation transformer?
HVAC transformer testing/troubleshooting
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What is a transformer & how does it work? HVAC/R
• HVAC/R: What is a transformer and how...
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How a Transformer Works:
Michael Faraday, the 19th century British physicist, made transformers possible when he discovered the phenomenon of magnetic induction. To make a long story short, a transformer uses induction to alter the voltage in an AC circuit, and it can either raise it (step it up) or lower it (step it down). An HVAC transformer is a step-down transformer that uses — as all transformers do — a pair of conducting coils wrapped around a metal core.
The primary coil receives the incoming signal, and as electricity passes through it, it induces a magnetic field in the core. That field energizes the secondary, or output, core, which in turn induces an electromotive force in the output coil. The EMF is directly proportional to the number of windings in the coil, so if the coils have different numbers of windings, the voltage in each circuit will be different. This only works with AC current because the electricity has to be in flux to induce a magnetic field.
The Control Circuit Is Isolated:
The electric signal from the transformer is used by the system to open and close a series of relays and contacts that control the various system functions. The way it operates a particular component, such as the blower motor, is something like this:
The neutral leg of the 24-volt circuit that originates at the transformer is connected to one terminal of a control relay that consists of a coil and a dry-contact switch. The hot leg is fed through the thermostat before connecting to the other relay terminal. When the thermostat switch closes and allows power to flow, it energizes the coil in the relay, which generates a magnetic field that closes the switch. The blower, which is powered by an independent 120- or 240-volt circuit, comes on.
Signs of a Bad Transformer:
As a passive electrical device, it's rare for a transformer to malfunction, and a certain amount of humming is normal. A transformer can malfunction, however, if there is a power surge large enough to damage the coils or wire contacts. When the transformer is damaged, the circuit breaker controlling the system will usually trip to prevent damage to any of the sensitive electronic components of the control system. The breaker can trip for a number of other reasons, and it usually takes an HVAC professional to trace the cause to a bad transformer.
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All Comments (21)
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This channel is invaluable. Thanks for sharing.
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This week I diagnosed a bad control board because I saw no LED light on the board.This york package unit had a transformer just like the one in this video, and I did not know how to test because I rarely see them and because of my lack of knowledge I didnt test. I more experienced tech went out after me and did all that you just did and the transformer had no 24V coming out which powers the board. Man, I feel so dumb. This video will save me!
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Thank you sir. You just saved me 13K on a new system the HVAC guy was trying to tell me I needed. Replace the transformer, and everything is now working perfectly. Cost $27.
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Brother , believe me you could make your self the best instructor if you open your own school. I had few old school instructors/ hvac gurus explain to me about transformer, yours by far is the best . Because you explained everything A-Z
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Very good lesson. Talk at the speed or us to learn, unlike the other fast talker trainers. Thanks
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Just what I needed! Needed to replace the transformer and was not sure if the 24V output was DC or VAC. Seeing your meter set to AC cleared that up for me. Now I feel confident I am ordering the correct after market transformer. Thank you!
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Brilliant! This is simply the best video on testing the transformer I have seen, period. I have also found that replacing the contactor is quite common and wise to replace both when the contactor is bad, which I guess many times will fry the transformer? Again, you made it super easy! Thanks bro.
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Very grateful for your excellent video. Last night we spent a very warm night at the Florida keys because our A/C would not turn on. I spent several hours last night trying to find the problem. This morning I watched your video and was able to find the control board with a blown fuse hidden under a couple of steel covers inside the air handler and fixed the problem. I had called several air conditioning companies and the soonest I could get one to come was tomorrow. Thank you again.
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Thanks a million. I just fixed my 38 year old a/c unit. Thanks to your videos. I'm not sure how much money you saved me(28 dollar part) but I don't care I wasn't going to pay it. Loool. Thanks!!!!!!!
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Man, such an informative video. I'm just a regular Joe that likes to fix my own hvac, and this was extremely helpful. I wonder how much money I have wasted on throwing away good transformers.
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Thank you, you did a great job explaining. Very clear and understandable. It helped me a lot.
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This was the easiest explanation of this concept that i can find. Thank you so much!
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Really appreciate this video. You’ve been a big help since I joined the industry a couple months ago
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Very helpful. I watched both of your hvac transformer videos before sucessfully replacing mine. All your videos are so helpful. Thanks again.
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Great explanation!! Thoroughly enjoyed that as it was so well explained. Very much appreciated
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Great video. Easily explained. Thank you.
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Thank God that I encountered to you this platform , you are a genius .
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Thank you so much for this video. After watching,I was quickly able to replace transformer ($15), get heat pump working again, saved $ by avoiding a service call charge.
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Super great video. Very detailed and finally someone explained in detail what the numbers mean on the transformer.
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Great job on the explanation and the demo board! Very helpful.
