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Old 07-17-2012, 08:35 PM   #1
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


Is it normal to have the wires that go from the control board of the furnace not follow the wiring digram? I don't think anyone touched the control board, although two contractors had worked in the area. But my current configuration is nowhere close to what is suggested on the wiring diagram... and it's not working. I'm wondering if I am best of to start from scratch and put all the wires back the way the wiring diagram suggests is.

Any thoughts?

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Old 07-17-2012, 10:15 PM   #2
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


Should match the diagram.

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Old 07-18-2012, 03:36 AM   #3
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


I've seen cases where one or perhaps two wires weren't in the right place, but overall the wiring should match the diagram. If someone has rebuilt the control circuits or wiring, or replaced components then the wiring may not exactly match, but that doesn't mean it's wrong. For example, replacing a 3 speed motor with a 4 speed motor, or replacing an old heat sequencer with a new and different style sequencer.

If you're not proficient at reading wiring diagrams, I'd caution you against doing something like this. Putting the wrong wire in the wrong place can cause a lot of damage (read: Expensive).

Was the system working before, with the "improper" wiring? If so, then I'd first find out why it's not working, and fix that before diving too far into the wiring.
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Old 07-18-2012, 07:58 AM   #4
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


Thank you for your reply! The problem I have is, two people who were "professionals" have looked at it and I have no idea what they touched or moved.

One professional came in, and when he left, he noted that the air conditioner might not work, but that the furnace would be fine as long as I hooked up only the white and red wires. So I put a two wire thermostat on the system and it worked perfect. At that time... the R from the control box was going to one leg of the Heat/Cool relay... while the W from the control box was going to the other leg of the Heat/Cool relay.

Those two lines come together, open the relay up for power, and it works. The only problem is, I look at the wiring diagram, and it suggests that two completely different color wires... going to two completely different places on the control box are "Supposed" to go to that spot. (Green wire to the G on the control box on one leg of the relay and Black wire on the C spot on the control box to the other leg of the relay).

The R&W made sense to me.... basic two wire thermostat kicks on... touches to two together, feeds power into the relay..... activates the coil, blower motor kicks on. However... thats NOT how the wiring diagram suggests it.

Any thoughts?
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Old 07-18-2012, 09:38 AM   #5
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


The tech should have told you why he thought the AC may not work.

If you rewire to match diagram you may find nothing works due to faulty AC electrical component(s) OR it may work fine. If it doesn't work call your service company and ask for a tech who really knows his stuff especially wiring. Also check that neutral to motors are not accidently connected to a hot wire. This can occur on the load side and not cause a short. It's a long shot but I have found this condition once in 30 years. DO NOT BYPASS ANY CONTROLS!!
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Old 07-18-2012, 10:50 AM   #6
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


Where did ya find those "professionals"

It's not unusual for older furnaces to have to be retrofitted with newer controls, and sometimes wiring colors won't match if the tech has to replace a burnt/broken wire. Don't focus on the COLOR of the wire, but rather on where each wire lands. If a wire is supposed to route from the control side of the sequencer to the transformer, then just confirm that wire is there, and don't worry which color goes where. I've seen plenty of factory wired machines that had the wrong color wire or tracer. It's annoying, but it happens.

I would be quite leery of starting a project like this if you're not 100% confident you can get it done safely.
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Old 07-18-2012, 11:19 AM   #7
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Is it normal to have the furnace control panel wiring, not match the wiring diagram


I appreciate the responses... thanks for the help. I am not really paying attention to the wire color, as much as where it lands on the control panel... I had thought the R & W on the control panel controlled the heating of the system. The way my system is currently wired, they go tot he heating and cooling relay... one on each side, suggesting that when they are joined together, they power up the relay and allow the power to pass through.

This makes sense to me. What doesn't make sense is that the wiring diagram suggests that the R & W go to completely different places. One each to the G on the fan cycle control and the other to the R on the fan cycle control.

I guess the question is... do the R & W from the control panel typically go to the heat/cool relay or the the fan cycle control?

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