honeywell furnace controller schematic ST9120U1003

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I've got a friend with a furnace that keeps blowing control boards.
They go out about once a year. Anyone know where to get the schematic
for this board? This is the 4th one replaced in his Heil furnace. I
searched and all we find is people selling boards, no schematics.
Thanks,
Charlie Luke

Re: honeywell furnace controller schematic ST9120U1003

On Thu, 06 Nov 2008 22:36:57 GMT, no snipped-for-privacy@bellsouth.net (Charles

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A quick peek at a photo of the board shows that it uses SSR's, quite
like the crap in my swimming pool system controller.

I temporarily solved the problem by wiring in a conventional
electromechanical timer.  When the "cool" season arrives I'm going to
replace the SSR's with real relays.

                                        ...Jim Thompson
--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: honeywell furnace controller schematic ST9120U1003
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Maybe they changed the board to SSR's.  The site I looked
at has a photo of the controller which shows regular
electromechanical relays, so he'll have to examine his
board to see which version he has.
http://site.famousparts.com/HONEYWELL/63-9570.pdf

Ed

Re: honeywell furnace controller schematic ST9120U1003
SSR's are indeed junk... and perhaps just wiring in some real
relays will do the trick. If you still want the schematic, just get
a tech to trace out the circuit and measure the component
values... that what I do whenever I need a schematic and have
a sample board.

Best regards,

Jean


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