I spent the last week using this forum based on previous users problems. I had a similar issue to others but not quite. I got it fixed and decided I would describe the problem and the solutions.

I have a couple of Amana central air systems in the house. One did not work at all (no blower, no compressor) this summer. The other worked perfectly.

I had old style mercury (Honeywell) thermostats. No batteries to check. The failed system had no voltage going to the thermostat. I swapped units and the failed system was still failed. (Not the thermostat.)

Took a look at the Amana blower unit. I was initially confused as there were two transformers in the bad unit and only one in the good. After looking closer, it looks like the original transformer was already replaced and the previous owner left the old transformer in the blower (it was not even hooked up after closer inspection.)

The new transformer had a slow burn fuse. After testing the fuse, it was bad. Replaced the fuse - still no luck.

Tested power going into the transformer (220V - good), but no voltage was coming out. (A burned out transformer.) Replaced the transformer ($14). Now the blower would work and the voltage would make it to the thermostat.

But when I turned on the AC - the blower would stop - and the new transformer was making noises. (Very bad.)

Tried a second time with the line to the outside compressor detached - blower worked with AC off and on.

I did some additional checking and it looked like there was no resistance on the wire going to the compressor outside. Looks like a short.

Traced it back outside and took the cover off the compressor. It was immediately clear that a mouse made its way into that compartment and had its way with a number of the wire insulations - including the 26V line coming down from the blower.

Once I replaced/patched up all those wires and plugged the mouse hole, everything worked like a charm.

It looks like the previous owner had issues and whoever fixed the unit last time re-ran the 26V wire to the compressor from the blower without a conduit. Hence leaving a hole large enough for a mouse. That caused everything else.

Good luck everyone.