On Sun, 10 Apr 2011 00:18:44 -0400, Jeff Thies
wrote:

On 4/9/2011 9:41 PM, wrote:
On Sat, 09 Apr 2011 19:22:57 -0400, Jeff
wrote:



But first do as I suggested in another thread,look carefully for
anything burnt and check the polarity of the line. Make sure the neutral
is neutral. You can measure from the ground prong. See the note in the
schematic. I'm not so sure this didn't arc to the transformer shell,
from looking at the pic. You may wish to measure voltage (AC) from the
transformer shell to a guaranteed neutral.

It's AC so there is no polarity. It's single output, non grounded, so
it doesnt matter which direction either the primary or secondary are
connected. Good to have the white on neutral and the bloack on live,
but it will have NO EFFECT on the operation. - or the life of the
transformer.


Except that the schematic has a note at the top that says:

Important
Integrated Control is polarity sensitive.
Hot leg of 120V power supply must be connected to the black power lead...

Whats with that?


I'm sure I am as baffled by that as you are. AC in not "polarity
sensitive" and as long as neither side of the primary or secondary is
grounded the control should not know which way the primary (or
secondary) is connected..

I would SUSPECT, but do not know for sure, that all the relays etc are
DC coils and all the circuitry on the control board is running on DC
provided by a full wave rectifier bridge on the circuit board., and
all the sensors also run on DC (and quite possibly - even likely - on
5 vdc, not 24)

Otherwise I would fully agree with you.

It seems to me there is a flaw in the integrated control and whereas
I don't see how this could be a problem, it is easy enough to scratch
off the list. Troubleshooting is little more than eliminating possibilities.

It would not surprise me there is a problem with the board. Trane has
"upgraded" the board from a white-rogers unit with their part number
CNT0377 to a new replacement kit, part number cnt05122 - which might
lead one to ask the question "WHY".


This can be pretty well determined by installing the fuse I (and
others) have recommended several times in the past.. If it blows the
1.5 amp fast blow fuse it is safe to say there MAY be a board problem
(or a shorted relaycoil, etc).




Jeff