blown transformer

jim lockard

Have you examined the wire at the outside unit, for both dog chews and weed wacker attacks?
Turn power off to both inside and outside units, Placing a small fuse in the low voltage circuit will help preserve xformers. Was the t-stat in cooling or heating? With your Ohm meter start checking low voltage coils til you find the coil that is short to ground. I would check the outdoor contactor coil 1st. Best Wishes J.Lockard

pat v

blown transformer

heres the problem. The system is 3 years old and has never had a problem, I have 249v going in and 29 going out and as soon as i hoock up the low volt and turn on the power the transformer burns out.i know there is probably a short on the low volt side but where should i look first and how.

Empire_2

Jim has it right.....

Chasing down a short is an Art and I have see guy's spend countless hours looking and looking and some find the problem fast. Call in a Pro if you have to. Since your short can be ANYWHERE, the system as a whole should be isolated to find out where.

bob_50

Beside a short

I have also seen x-former fry when mice get into the control box and get debris in the contactor preventing it from pulling in.

kal_2

go to radio shack...

and buy a lamp holder with a 24v bulb - disconnect one of the leads of the 24v output and put the 24v bulb in-line - it should burn brightly, and wont short out, and now you can go and disconnect section at a time until the bulb burns only half bright – indicating a normal load, if it goes out completely then you have disconnected everything and need to back-up – now you can easily go step by step and find your short – without worrying about a burnout – also look where wires go through holes as vibration usually wares them through to the bare metal - this is not rocket science – I personally use 2 12v pizo electric horns in series so I can hear it without looking - but don’t do it when the HOs are around they don’t take well to loud sounds

Empire_2

OR

You could buy tools like a clamp on ammeter and learn how to properly track down shorts.

Barbarossa

Go with the bulb kid.

The ampmeter will not limit the short current and the Xtmr will blow again the lightbulb load is a better bet for limiting damage and costs.

mtfallsmikey

Inline fuse with alligator clips attached

Works well too...strangest thing I ever saw in a condensing unit J-box was a baby mouse and small copperhead snake, both fried when they got across the contactor...no joke!, but the only witness to this is no longer with us.

Empire_2

I believe you Mikey

I have found both myself. Only once though. The mouse was skeleton and he bit in one of the wires and grounded itself out. Strange........

Mike T.

dana_3

blown transformer

you can get at radio shack a 3 amp mini .lo voltage circuit breaker. disconnect the lo- voltage wiring at the furnace or air handler 24v trans.attach one leg of the mini breaker to the R terminal, and the other to the Rwire to the tstat. then as you rewire each other item back in.(with the power off ) as they get wired in. turn the power back on. you will then find your problem. without a need for a bunch of 24v fuses or transformers. OR you could call in a tech to troubleshoot for you

Empire_2

In a short,.....?

All I can say is USE your clamp on ammeter and there will be no need for horns, a trip to Radio Shack, or buying a bulb to do what was mentioned. No disrespect, but are you men kidding me? I guess if it works and you are comfortable,... go for it. I guess to each his own and I am sorry if I ruffled any feathers, but any short can be found in 3 minutes or less with the tried and true clamp on ammeter. Please don't take this the wrong way, but this is one question that I am passionate about.

Peace.......

Mike T.

pat v

thanks

thanks for all the great suggestions. I found the prob it was in the contacter coil.

mtfallsmikey

No ruffled feathers here, T

As you say, to each his own. seems like in the old days, a 24v. transformer was..."tougher"? I've seen anticipators fry on T87's before the xmfr. would go. Your clamp-on works for you, but I was taught to do it a different way...More important than tools is the technique, and all of the above will work, but troubleshooting anything requires common sense and a logical sequential approach. Ladder diagrams, which were NOT included with equipment schematics back in "the day" make things a lot easier..you can "see" how each device is powered, and in what order, start to finish. I wish more people in our industry had your passion, and pride in their work. I guess it has something to do with how and by who we were trained by. i've been very fortunate in that regard.

Empire_2

Like my Father said before me:

What the hell are Ya doing with that clamp on meter,....You don't need that!!!:-)

Mike T.

kal_2

lucky you...

thats a rare one, open coils or fuzed contacts are far more common - as well as abraded through insulation

kal_2

yep...

a stupid bulb in series with a start or run capacitor will test it fortwith..

off = open - dead

full brightness = shorted - dead

medium brightness - for run type and half brightness for starting type = good

jim lockard

Contactor

Bad contactor on the outside unit as I predicted, not bad for a cyber trouble shoot. Glad you got it fixed. Best Wishes J.Lockard

Eugene Silberstein 3

Brings back memories

That brings back memories of my dearly departed father. He was full of tricks like that.

I, personally, was never a big fan of his tricks.

kal_2

so what did you use before...

the "capacetance" range on your DMM ??? - dont tell me you were a "parts changer"

Eugene Silberstein 3

I have been fortunate

I have been fortunate enough to have been raised in the era of digital (at least decent quality analog) meters. I still enjoyed my old man's stories (and lectures) though.

Now I get to lecture others...

Unknown

Personally,

I like to replace my burnt transformer with one that has the little breaker built in and then test each circuit separately to see which one blows the breaker. I always replace a bad transformer with one with the little breaker, it just seems like the right way to do it.