Guy came out for service call. Replaced the 5 amp fuse and said I want
my check. I was happy it was running but really expected more of an
analysis of what might have caused the fuse to blow. He didn't even
wait for it to cycle through a full on-off-on heating cycle.

Next time I'll just replace the fuse myself...which I would have done
if the panel for the air handler wasn't sort of sealed. Now I know
better.

My concern is whether the fuse blew during a defrost cycle and that it
might simply do it again.

Anyone know how often or what triggers a defrost cycle?

The weather here has been highs in the 50's and lows in the mid-30's.
I'll feel happy after it stays running through a defrost cycle but
have no idea when one would occur. He mentioned that they trigger
during colder temps and I was thinking it might take a while until one
got triggered.

thanks

-Phil


Don Young wrote:
"Zyp" wrote in message
news:47ydnaqhTof3QLLanZ2dnUVZ_tCrnZ2d@championbroa dband.com...

Phil;

Control transformers do not go out on their own. Somthing must short out
the connection and cause a failure. Check the 5 amp fuse. If it is
blown, you've got somthing that may be shorted. There is a line running
to your new outdoor unit that should have from 5 to 7 wires in the cable.
If the installer mis-wired the control board, he could have smoked the
transformer on the call for heat. Or, he could have mis-wired the defrost
cycle wiring. When the outdoor unit called for defrost, it signals the
indoor unit to energize the auxilary heat. So you should mention to your
installing contractor that maybe there's a problem and that he shouldn't
charge you until it's decided what the actuall failure is.

--
Zyp

Transformers (and inductors) do not wear out and are among the most reliable
of electrical/electronic components. They most often fail from overheating
due to excessive current draw or from lightning or other high voltage
surges, but they are not immune from inherent failure by themselves. As in
many other component failures, it is often caused by a manufacturing defect
such as poorly soldered connections, misplaced insulation, sharp edges
puncturing the insulation, breakage of too tight wires, etc..

Don Young