home hvac problem / question

Soundguy · Feb 1, 2015

Trane unit, compressor outside, air handler in garage, etc. Unit runs on cool fine, shift to heat, and shortly the digital thermostat goes blank, and a 5a fuse blows in what appears to be a 24vac transformer circuit near a big relay in the air handler.

I'd just like to sound Intelligent when I call the repairman, vs like a sheep. Don't want him to tell me my turbo encabulator is bad and i need a whole new unit

History: Unit 15 ys old, otherwise ok shape. Filter each month, has had checkups every couple years. Has been thru 1 cap and fan motor outside, plus had the a coil removed and cleaned once after a cheap filter disintegrated plugging a coil. Ac comes right on, cools good.

Thanks for some ideas

Professor Marvel · Feb 1, 2015

I believe the major change from heat to cool in a heat pump is just the reversing valve. is that in line with the fuse that blows? It is a solenoid control. But I think Trane releases it for heat. IE in needs to be energized to cool. To eliminate it unwire it and put it in heat and see if it still trips. How cold is it there? Is it possible it is cold enough for your electric backup/emergency heat to be coming on?
Does the compressor come on before it trips?

davesl708 · Feb 1, 2015

My first thought would be to look at the thermostat for proper functioning. If you are familiar with a multi-meter shut off power and ohm the transformer to see if it is shorting out.

arlen4720 · Feb 1, 2015

Soundguy said:
Trane unit, compressor outside, air handler in garage, etc. Unit runs on cool fine, shift to heat, and shortly the digital thermostat goes blank, and a 5a fuse blows in what appears to be a 24vac transformer circuit near a big relay in the air handler.

I'd just like to sound Intelligent when I call the repairman, vs like a sheep. Don't want him to tell me my turbo encabulator is bad and i need a whole new unit

History: Unit 15 ys old, otherwise ok shape. Filter each month, has had checkups every couple years. Has been thru 1 cap and fan motor outside, plus had the a coil removed and cleaned once after a cheap filter disintegrated plugging a coil. Ac comes right on, cools good.

Thanks for some ideas

Is there a schematic in the door? If so, take a picture of it and post it.
The reversing valve would be a good place to start, if it's sticking, the solenoid would over amp. Most of them de-energize to heat, but some in the southland energize to heat.

merlynr · Feb 1, 2015

Can you go to emergency heat only?

murphy1244 · Feb 1, 2015

davesl708 said:
My first thought would be to look at the thermostat for proper functioning. If you are familiar with a multi-meter shut off power and ohm the transformer to see if it is shorting out.

That would be my first check too and the wiring that completes that circuit.

swnoel · Feb 1, 2015

Could be a chafed wire or bad solenoid... any rodents enjoying a warm motel room in your condenser?

davesl708 · Feb 1, 2015

View attachment 409671

Here is a problem I had with the outside unit. Have since replaced HVAC with geothermal ground loop.

Looking4new · Feb 1, 2015

Soundguy, your thingamajig is shorting out the whatchamacallit and it will cost you mega bux to replace with a new unit that will only last about a year or so with its' lifetime warrantee. (Whos lifetime?) The lifetime of the faulty parts installed to begin with.

Seriously, I would look at the thermostat first.