24vac transformer has strange symptoms

[acman0001]

Hey guys I was just installing this trans in a split unit system and when you cycle the a/c to on the fan is spinning slower than it should as soon as the cool shuts off then the speed of the fan kicks up again. while i was installing it I accidently wired it for 240 and the trans hummed really loud so i shut it off and wired it for 120 now it seems as if I have degraded the life of the trans when it hummed so loud. So Im thinking that the trans can do the fan fine but, when i switch the unit to on and the trans has to provide for the thermostat and the contactor and the fan it just cant do it all now. what do you guys think?

shaun a\c man

[keepitsimplestupid]

That 24VAC secondary, guessing here, became a 48 VAC secondary for the duration of the mis-wire. Hard to tell what got damaged or degraded.

[ruud-man]

It sounds like you are energizing more than one blower speed at the same time. Better check the wiring and/or board.

The tranformer does not supply power for the blower. The over voltage probably damaged the control board if there is one.

Pull the lead for the heat speed and see if the blower runs normally in cooling.

Good luck...

[Wild Leg]

If he had 120v power supply, and hooked up a 240v tap from the transformer, wouldn't he have had only 12 volts?

[ruud-man]

Sounds good to me. In any case check for two speeds trying to run at the same time,

[skeeter_22]

Maybe I'm missing something.....but why didn't you run 240? By split do you mean you were wiring the A/H up? If so...then I assume most are wired 240. You need to add that other leg for it to work. Are you wiring the high voltage into the heat strips or into the trans?

[Wild Leg]

From his original post, I assumed his indoor section was a gas furnace, supplied with 120v. He had installed a one-size-fits-all multitap transformer, and inadvertedly chosen the wrong tap.

If it is an electric furnace, then he needs the 240 volt tap, as he is now furnishing 48 volts.

He's still got problems, but I don't think they are from a bad transformer. (I guess it could be, if the transformer is not developing 24 volts.)

I have to ask, what killed the first transformer?

[smokin68]

Originally posted by acman0001
Hey guys I was just installing this trans in a split unit system and when you cycle the a/c to on the fan is spinning slower than it should as soon as the cool shuts off then the speed of the fan kicks up again. while i was installing it I accidently wired it for 240 and the trans hummed really loud so i shut it off and wired it for 120 now it seems as if I have degraded the life of the trans when it hummed so loud. So Im thinking that the trans can do the fan fine but, when i switch the unit to on and the trans has to provide for the thermostat and the contactor and the fan it just cant do it all now. what do you guys think?

shaun a\c man


After reading this post all I can say is WTF??? A/C shuts off, blower speeds up. Transformer has nothing to do with blower speed. You need to call a pro before you fry something.

[corny]

People should really be clearer in their posts... split system sounds like a heat pump but could very well be a furnace and blower..

There should be a top posted and sticky post at the top of each section that tells the people contemplating posting a question that they need to be as detailed and specific as possible so that folks on here who are willing to help can give the best possible answer or solution.

[keepitsimplestupid]

Wild leg:

Transformer lesson using easy numbers.

V1/V2 = N1/N2 where N1/N2 is the turns ratio.

Say we have a transformer 125V:25V or a ratio of 5:1, so it steps down by a ratio of 1/5.

So if we apply 250 V and we step down by a factor of 5, the secondary would be 250/5 or 50 volts.

Transformers are perfectly happy working the other way to0. The same transformer can step up 25 volts to 125 volts if you reverse the primary and secondary. You can wire the secondaries in series and parallel. In parallel the secondaies must be the same voltage and the available current will be the sum of both. In series, the voltages can add or subtract depending on phase.

[comfortdoc]

I think an experienced technician is needed here to see what's going on.