wiring a new airhandler

smitty_6

wired a new goodman airhandler and cant seem to get 24 volts to the t-stat all wiring seems correct any suggestions 

Techman

24vac

No 24v to stat as in a 24v HOT and a Common or just a 24v Hot and a Y & G switch leg?Recheck the wiring ! Is there 24 v @ the xformer? Is the control fuse open?Is the stat & or the system a  heat/cool w/1 or 2  24v xformers? What stat r u using?

smitty_6

wiring a new airhandler

just 24v hot and a Y & G switchleg. getting line power into transformer no power out of 24v side using a pro1 T705 t-stat

Techman

24vac

What is the line voltage ? 120 or 240? If the line voltage matches the unit voltage then the xformer is no good ,unless  the xformer has a built in  circuit breaker or fuse. Did you check for  the low voltage AT the xformer terminals?

Wayne_16

Sounds like the transformer is shorted out.

When line voltage is measured at the transformer power leads and no output voltage, most likely the transformer was shorted out.  Check for 24 volt output to the control board inline fuse if available. 



Ohm out each side of the transformer; the 24 volt side most likely will ohm out fine the 120/240 side will ohm with an infinity reading.  The windings are very fine on the power side of a step down transformer and will burn out easy if the low voltage wiring has been shorted.



Install a 3 or 5 amp fuse in the low voltage side when replacing the transformer to prevent any accidents in the future.



Minnesota Wayne

Jean-David Beyer

Are transformers still made like that?

I thought modern transformers for doorbells and things like that, were made with barely enough iron in them so you could short out the secondary and not even pop the circuit breaker on the primary. They would probably buzz some, but that's about it. Nothing would prevent the fuse on the secondary side from popping if the shord were after that. In other words, there might be a shortage of 24 volts, but with modern transformers, they are less likely to burn out.



No harm in testing them with an ohmmeter, after they are disconnected from the other circuitry, though. Murphy's Law still applies.

Wayne_16

The primary winding opens when the secondary is shorted.

They still burn out in my field of work.  Granted they may take a hit and not open the primary the first quick short, but they will burn open. 

The fuse on the secondary lead will protect the transformer if there is a short after the fuse.



Minnesota Wayne

TATTOOTOM

Smoked transformer

If you have a smoked transformer than you probably have a short in your low voltage wiring. You will have to find the short and wire an inline fuse on the secondary side of the new transformer you install. That will save the new transformer in case there is another short in the low voltage wiring.