Replacing Control Module

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Old 10-05-04, 02:06 PM
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Cool Replacing Control Module

Is it easy to replace an obsolete control board with a universal control module? Will the harnesses and molex fit from the old to the new? Should I worry about the timings and default switch settings?

My original problem is that my blower wont run. Replaced capacitor, still wont run. Meter does not read 120v for motor. Removed motor and tested, motor works fine. Now focusing on control board.

Please advice...
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Old 10-05-04, 06:03 PM
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Lightbulb Replacing the Primary Control Module

I just replaced my primary control module on my 1995 Tempstar Oil Furnace
with Heating and Central Air Conditioning. The symptoms with my situation,
When switching the Tstat from, AC to Heating. The primary control
for when the tstat called for heat. The primary control would just buzz!
I obtained the correct service manual for my
furnace from the installer. Inside the manual should be a control wiring
diagram along with a ladder logic diagram with voltages.
I switched off the furnace circuit at the entrance panel. The test for voltage around the the primary control module, 120vt
line coming into the furnace motor. Then I removed the cover to the primary
control module and noticed black marks on the control board where a short
had occurred and further investigation noticed that a leg on the 25 vt relay was burnt in half.
I final located a replacement for the primary control module, Installed the new module and after double check the wiring for the module ($105.00). Reset the circuit breaker and turned on the Tstat for AC and then Heating , all was good!!!!!
I hope this infomation helps.

Old 10-06-04, 05:14 AM
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Cool Reply: Replacing Control Module

Thanks for your response. Did you have to make any adjustments to your connectors (like removing wires and rearranging them)? That is the only concern that I have. Plus did you replace your module with an exact copy of a universal? Any input is a plus...
Old 10-06-04, 02:16 PM
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Cool Replacing Contol Board

P.S. - The old printed circuit board has a part number of 031-01140-000. The replacement control module (encased) is a White Rodgers 50a55-843. There are several cross products that are posted over the internet that replaces the original but seems to be obsolete as well. These are 50a55-438, 50a55-286, 031-01140-001. I am willing to do the work to replace this but am without experiance in the wiring. By experience, are all molex from old to new part compatible? Can this be just a "plug and play". Please advice...
Old 10-06-04, 04:16 PM
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Replacing Primary Control Module

Yes the wiring on the original module was a white, orange, and black wire
going to the limit switch, ignition transformer, and 120vt coming from the fan relay, which was just replacing the orange with orange,ect!
The only problem which I encountered was the original board had seven electrical connectors for which 2 for the flame sensor and 5 electrical for the heating and cooling Tstat.
The new board for the primary control module
had a total of 5 electrical connector, I had a small problem with connecting
the grounds with the Tstats, but after much thought, I arrived at the correct

I hope this helps!
Old 10-07-04, 07:34 PM
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Cool Replacing Control Module

Thanks Idrotos,
Will give it a try. Replacement part is not much ($90). Hopefully the wirings from old to new will be obvious. Will post results for future reference.
Old 10-14-04, 07:01 PM
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Replacing Control Module

Posting to complete thread. Replacing Control Board worked and blower now working fine. No rewiring necessary on molex or connectors. Pretty much removed all wiring/connectors on old board and plugged in on new board. Also changed timing switch settings on new board to match timings from old board. Tip: about the only thing you may need to know is it may help if you have a little background in electrical or electronic before you attempt this, otherwise it may be best to have a service technician to do this for you.
I'm all for DoItYourself...
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