HVAC shutdown- youve helped before

[Noah Darrow]

Good afternoon,
I post here b/c i had had a problem in the past and found the experts here to be very honest and knowledgable.

I have a Lennox heat pump and Bryant air handler in the attic. Yesterday, I shut down the system during the morning, when I turned it back on...Nothing.

I tried moving the fan from AUTO to ON, still nothing.
So far I have:
Checked and reset every circuit breaker- no issues
Removed the thermostat (battery operated) and replaced batteries
Went outside and pulled the big 4 prong breaked and put back in.

Ive checked the flood breaker, no water and not triggered.

I looked for a switch on the air handler which I may have hit accidentally while in attic, I cant even find a switch that I may have hit.

I have a friend who knows, but doesnt repair HVAC and he suggested that it may be the transformer in the handler.

Does this prognosis make sense you the trained experts?
Is there another obvious culprit.

I, and my pregnant wife would be much appreciative with any reply.

Thanks much in advance.

Noah

[Bruce A. King]

Yes, the transformer or a small fuse somewhere in the attic unit that is in that transformer circuit. Many are automotive type fuses. 3 to 5 amps usually.

[Wayne B. Wilson]

Check the fan door also