On Tue, 19 Dec 2017 10:35:17 -0000 (UTC), "Danny D."
wrote:

Normally the Generac generator feeds the whole house.
No fuse is tripped and I switched them all anyway (like everyone does).
What would make a generator only feed half the house? (if that)

At first it wouldn't go on automatically - so that may be a clue.
I had to switch it to automatic from manual and after a dozen of those
switches, it went on automatically.

I'm wondering how to debug the transfer switch but I opened both up and
they seem to be the same with no moving parts.

Any ideas?
Check to make sure the generator is putting out 240 volts (120 on
each side, line to neutral) If it is, you have a transfer switch
problem. If not, you have a generator problem.