Troubleshoot challenge!Bad transformer?

[grodan1]

Service call.Furnace not working.Troubleshooted down to transformer.Checked voltage in.Verified 120 v. going in by clamping vom to black and to ground.No power out on 24v side.Replaced transformer 3 times, same result.Solutions from all welcome.Bad shipment of transformers or what?

[karsthuntr]

You better recheck your meter or where your reading from. Ohm out the x-frmr.

[grodan1]

Ohmed out all three transformers.All good.Used two different meters-same results.Read from black to furnace body to ground and complete circuit.Same results.

[hot wired]

try checking volts to netural instead of ground. is this a multi volt trans?

[willy1]

did u check for neutral on incomming power

[danielworkerbee]

Better install an inline fuse on new transformer while working on bad transformer jobs.

[Milk man]

Don't check nothing to ground. Always check between L1 and L2.

You should be able to check L1 and L2 right at the x-former.

If you have potental on L1 and L2 then do you have potental at R & C at the x-former.

You might want to ohm out those "bad" transformers. If they are blown, put a fuse in the low voltage side.

So how much training have you compleated?

[grodan1]

You got me!I'm a student at a trade school and I was just wondering why three fellow students and TWO instructors could'nt figure that one out without replacing even one transformer.I had them go to neutral and they got 40v instead of 120v.I looked in ceiling and the neutral came loose from a pig-tail in juncture box.

[karsthuntr]

I bet he is using a 230V x-frmr on a 110V circuit.

[grodan1]

I've been going about a year, and if you think that story is scary- I have more even worse.

[control_noob]

Come back and see us after your first week in the field there killer... I would seriously re-evaluate any school that has instructors who would teach checking for voltage in this manner.

[grodan1]

I just had an instructor proudly show me an electric furnace he said only used contacters and no sequencers.I asked him to show me it and he said here it is!See!No sequencers!And straight ahead at eye-ball level were the heating coils with wires going directly - five inches away- to two sequencers. I asked him one more time if he saw any sequencers, and he said no!

[grodan1]

Is there any way the industry can get involved directly with these trade schools? After all, these graduates are going to wind up in the field working on their equipment, so wouldn't it make sense to start leaning on trade schools by lending endorsment to good ones and setting requirements?

[trane]

Do you no the difference between sequencers and contactors?

[grodan1]

That wasn't fair.Contactors use magnetism, sequencers use a bi-metal activated by heat and the two do not even look the same!My point is how the heck does an instructor not no the visual difference between the two at a glance. I mean the wires from the heating elements went directly to the sequencers and he was pointing to the contacters.Sequencers are time delay switches and magnetic switches open and close instantly.

[docholiday]

Ive seen older ones without sequensers, they simply had quiet contactors and limits... Maybe, just maybe you were looking at limits.

[karsthuntr]

Some new airhandlers have contactors instead of sequences.

[grodan1]

Fair enough. I'll check it out, but the contactors were not wired to the elements to be fair to me.My memory tells me these "sequencers had low voltage connections for the "load" of the switch, and separate connections for the power they were passing, but I will make sure.Limit switches don't have the same visual as sequencers, so I know I'm right.Same instructor said you could get total cfm from a gas furnace by amping out blower motor and using formula amps x volts = watts x 3.413 = BTU'S and dividing TD x 1.o8 into those BTU'S!Insane.

[aircooled53]

That's nothing 1984 had a technician out of ATI school told me he needed to learn a little bit. The first couple of days he rode with me I asked some simple questions and he could not answer not even one.I walk him through a few calls in the summer as it was almost over and fall start up were soon. I asked if he new about heat pumps, oh yea our teacher was a heat pump specialist. The first unit we did was Coleman Heat Pump I siad go ahead and hook up my gauges ,I am going inside to check filter and blower and turn on thermostat. Came back to my New brass gauges were on the wrong lines, I thought you said you knew heat pumps.

Well, I got a couple of new gauges and after alot of work he turned out to be a great technician, he now works for Dyna-Ten Corp.and works on high rise buildings.

[trane]

I new a young man once that knew quite a bit and thought he knew everthing. Now I just wish I knew what I thought I did at 25. You are probably at the top of your class and I can tell that you know quite a bit, but trying to prove it on this board will be one challenge after another. It takes someone that wants to learn (like you) to ever make it in this field and it would seem that you are on your way. I once was in a school like you and most students were there to get out of something else and not because they wanted to to be. This was a tech. school in high school.

[Edited by trane on 03-08-2005 at 08:48 PM]