We just got a new heat pump/furnace/airconditioner installed (Trane) and you can hear the "buzz" of the transformer on the outside unit all of the time. Our old unit did this, but I always assumed it was because it was getting old and something was wrong. Is this normal? And why is the transformer "on" even when the unit isn't running. I'm not an electrician expert, but I do know that, for example, the transformer on a doorbell doesn't buzz until it's activated/in use. So why would a heat pump transformer constantly buzz or be activated?

Thanks for any help,
JG

I would go back to the installer. Most transformers buzz a little, but that sounds excessive for a little control transformer. If the installer won't help, contact Trane directly. I am sure they want to hold up their fine reputation.

Transformer 101. Transformers have 2 sets of windings, the primary and the secondary. The primary connects to the house wiring or other source of power. The secondary connects to the load usually at a lower voltage. For some uses, there may be several secondary windings or taps. Thermostats, doorbells, etc. use lower voltage to avoid running full voltage all around the house and to make switching easier. Usually there is a switch at the furnace that you can use, or the circuit breaker, to cut all power to the furnace. Unless you are using central air controlled by the same thermostat, you could turn it off while resolving the problem. With the switch in the on position, there will always be power to the primary windings, and a cycling magnetic field. The slightest loose metal in or near the transformer will vibrate causing the buzz. The bigger the transformer, the more likely it is to buzz. I am not sure how buzzing affects the life of the transformer.

You are right, most small transformers buzz little if at all.

If you have a split system you shouldn't have a transformer on the outside unit. They are usually located on the inside unit. Transfromers in the indoor unit has voltage running to them all the time, 240v or 120v on the primary side and 24v on the secondary side. Now it shouldn't be "buzzing" loud enough to catch your attention. Depending on how long ago you had it installed you might have a warranty on it and I would call the contractor who installed it.

What you are probably hear in the outside unit is maybe the contactor
But you are right even if it's the contactor,it shouldn`t buzz when the tstat is not calling for the unit to be activated
Tranes are noisy and louder than most a/c or heatpumps,, another reason why trane isn`t very popular in my area,, that and the fact when it comes time to need to replace parts they are sometimes harder to find

The transformer probably has loose laminated iron plates. The vibration or buzz is caused by the iron plates. This is in the core of the transformer that the wires are wound around. Usually a voltage problem or load problem can cause this as well as a poorly assembled transformer from the manufacturer.