HVAC Electrical Issue: Current Leakage from Furnace

[Averagesupernova]

Ok, you are introducing a lot of things here. Simplify simplify simplify! Start by turning off the main breaker and ALL other breakers in your house. Measure the cable feeding your furnace. You may still have current showing. It's not uncommon for ground paths to carry current through the water system. It's not out of the question for it to show up someplace like this. If you do have current showing here there's likely little you can do about other than hunt around to verify the path.
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Assuming the current has fallen to zero, start turning on breakers. Start with the main only. Watch your meter and turn on one breaker at a time while keeping an eye on your meter. Leave the furnace and A/C unit until last. Let us know the results.

 

[UrbanFarmEngineer]

Nice! OK will do. I will post my results.
I am on an isolated ground for my home i.e., a grounding plate, my house it not grounded to the water system so we can scratch that off for sure.
Let me do those tests and then get back.

What about the pic of the wiring diagram? Does it look like the condenser common and hot are reversed?

 

[UrbanFarmEngineer]

Nice! OK will do. I will post my results.
I am on an isolated ground for my home i.e., a grounding plate, my house it not grounded to the water system so we can scratch that off for sure.
Let me do those tests and then get back.

What about the pic of the wiring diagram? Does it look like the condenser common and hot are reversed?

Oh, and also since I last posted my electrician confirmed that the line to the furnace and the AC line are isolated so there are no shunted neutrals or anything like that happening here.

Just a Note: When I get the stray current on the furnace line and the AC line, ALL of it goes away when I turn off the furnace breaker.

 

[Averagesupernova]

Ok, again, simplify simplify. We know flipping the furnace breaker makes the problem go away. Start on the other end. Disconnect things until the imbalance goes away. It's possible the current imbalance is from the low voltage source in your furnace. Colors on wires don't mean anything except for convention. This is important of course, but without knowing which color is hooked where on the other end, who knows...

 

[UrbanFarmEngineer]

Yes, I have narrowed it down to inside the furnace playing with it and testing it over the past few months. OK will start with the furnace first. Maybe I should open the AC and see which color is the common and which is the hot (what do HVAC ppl call the 'hot?)?

Are the terminals in a typical condenser unit labeled? SO if I were to open it I could tell which color they've hooked up as the common?

 

[Averagesupernova]

Are the terminals in a typical condenser unit labeled? SO if I were to open it I could tell which color they've hooked up as the common?

Likely.

 

[UrbanFarmEngineer]

Likely.

OK good place to start I think?

 

[Averagesupernova]

OK good place to start I think?

You need to be isolating. When the current imbalance goes away, you are closer to the solution. It's really no different than you flipping the breaker and noticed the imbalance went away. Divide and conquer I believe is one way of describing it. Remove low voltage wires at the furnace or the other end of them. Your choice.

 

[UrbanFarmEngineer]

You need to be isolating. When the current imbalance goes away, you are closer to the solution. It's really no different than you flipping the breaker and noticed the imbalance went away. Divide and conquer I believe is one way of describing it. Remove low voltage wires at the furnace or the other end of them. Your choice.

OK so I have been working at it and traced it back to this:

Here is my question:
What should this look like practically:

• Hot is coming into Molex terminal 1
• Another wire leaving Molex Terminal 1 going to Blower Motor

What I have inside my furnace is this:

• BLK Hot bypasses terminal 1 of Molex Plug on board
• BLK Hot is put through a connector (heat shrink butt connector..?) and turns into a BROWN wire
• BROWN wire is then put through another connector (spade connector..?) and comes out as 2 brown wires
• One BROWN is looped back and attached to terminal 1 on the board
• The other goes on to the Blower Motor

The pic below, hard to see, circled is one of the brown wires after the split being inserted into terminal 1 of the plug on the board.
Right or wrong?

 

[Averagesupernova]

So what you are saying is the diagram doesn't match the physical wiring? You need to draw something. I'm not going to try to decode your description. Make a schematic. It's unlikely that it is actually wired as the diagram shows. If the breaker is turned on, then the blower would run all the time.
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Just exactly how did you arrive at 'traced it back to this'? Did you isolate the two units as I suggested? The idea is to shrink the number things involved until there is very little left.

 

[UrbanFarmEngineer]

OK I will draw a diagram.

I traced the current imbalance and did continuity tests on the components along the way--everything was OK-and as I kept going I came upon this wiring error.

I will try to take a picture to better explain it's just way back in the furnace.

 

[Averagesupernova]

You still don't seem to understand why you need to isolate. Of course you traced the imbalance to the place you circled. It's basically the first stop. Unless the current is leaking in the door switch, the amount of current around the place you circled will be them same as the hot wire on the way from the breaker panel.
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It's likely not what you refer to as a wiring error. Not sure why they do this but there is likely a good reason.

 

[UrbanFarmEngineer]

I did continuity testing on the whole furnace, section by section, piece by piece.
Everything else was OK
So I traced it back.... it is not that it is the first place it is just that the wiring is not as per the diagram in that spot and that spot only. That is why I am asking you guys if it is OK. Let me draw something and post it and you can tell me if it is a problem.

Sorry I am just extremely tired and not explaining this sufficiently.

 

[UrbanFarmEngineer]

I tested everything components and even the wires themselves. I found one spot where a wire was pinched and had copper exposed and it was touching the cabinet and leaking some current onto it but that wasn't the main problem although it took some of the stray current off of the main line.

Sorry again I am just incredibly exhausted from work.

 

[Tom.G]

Sorry I am just extremely tired and not explaining this sufficiently.

Aww, heck! Get some SLEEP. We, and the problem, aren't planning to go away.

 

[UrbanFarmEngineer]

Thank you. We ran into a last minute glitch in a formulation project that I was a part of and I haven't slept at night in a few days. haha I am half asleep and the other half crazy. Sleeping between 6:00 AM and noon makes it feel like time is melting.

I was working on the furnace for fun between project breaks.

The last thing that I can sensibly do or want to do right now (sorry @Averagesupernova ) is to make a diagram before I regain my sanity.

Can someone be so very kind as to tell me how you'd wire that little bit in the circle at contact 1 on the Molex so that I can start thinking about it during bout of semi-consciousness?

Also this is a noob question because I don't wire things for a living... what the heck is this type of connector called because this is what I have in the place where I believe there may be that wiring error.

 

[UrbanFarmEngineer]

OK here is the best I could do on my Chromebook with the mental resources that I currently have access to:

Manufacturer's Diagram (Close Up of Relevant Section)

The Wiring in my Furnace
(The Best I Could Do With What I Got)

Seeking your advice. You guys do this for a living and I don't but I can learn if you are willing to teach.

 

[UrbanFarmEngineer]

How is it possible that the same amount of current is going to flow to contact 1 in the first diagram as in the second?

 

[Averagesupernova]

Can someone be so very kind as to tell me how you'd wire that little bit in the circle at contact 1 on the Molex so that I can start thinking about it during bout of semi-consciousness?

How we would wire it is not relevant. You need to provide a diagram of how it IS wired. If you have in fact done so then I question the accuracy. The way it is shown would have the blower motor running all the time. This does not seem right.
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How is it possible that the same amount of current is going to flow to contact 1 in the first diagram as in the second?

It doesn't matter what goes into contact one. It matters that whatever total current goes into the furnace assembly on the hot wire also comes back on the white wire. Wherever it branches off inside the furnace is not relevant.

 

[OUcafe]

Most likely the current consumed from your thermostat to maintain sensor and general operation.

-JA

 

[Averagesupernova]

Most likely the current consumed from your thermostat to maintain sensor and general operation.

-JA

Current is not consumed. What goes in has to come back out. The issue is that it's not. It's getting away someplace else. Leaking back through an alternate path. Or, one thing I've suspected is that the low voltage that goes to the outdoor unit is leaking off. This may go back through the ground of the outdoor unit and find it's way back through the ground on the furnace. This is why I've asked the op to isolate the two by disconnecting the low voltage wires between the two. I have apparently been unsuccessful in that.

 

[UrbanFarmEngineer]

How we would wire it is not relevant. You need to provide a diagram of how it IS wired. If you have in fact done so then I question the accuracy. The way it is shown would have the blower motor running all the time. This does not seem right.
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It doesn't matter what goes into contact one. It matters that whatever total current goes into the furnace assembly on the hot wire also comes back on the white wire. Wherever it branches off inside the furnace is not relevant.

The fan is always running you are right.
The fan cannot be turned off at the thermostat either.

The only way to get the fan to go off is to shut power for everything down at the thermostat.

 

[Averagesupernova]

The fan is always running you are right.
The fan cannot be turned off at the thermostat either.

The only way to get the fan to go off is to shut power for everything down at the thermostat.

Ok. Now we're getting somewhere. I would not want it that way but whatever. I'd say your schematic matches your physical wiring.
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Now we are back to unhooking the low voltage wiring that goes to the outdoor unit if you haven't tried it already. If you have, we haven't heard what any of your findings were.

 

[UrbanFarmEngineer]

Ok. Now we're getting somewhere. I would not want it that way but whatever. I'd say your schematic matches your physical wiring.
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Now we are back to unhooking the low voltage wiring that goes to the outdoor unit if you haven't tried it already. If you have, we haven't heard what any of your findings were.

Sorry I haven't posted results. I have been so busy and tired that I thought if there was nothin to see in a particular place I'd move on. But I see now that I should have answered your question to keep you in the loop since I am asking you for help after all!

OK here is what happens with the condenser:

• When the AC is connected and running the net current on the dedicated AC line and the dedicated furnace line are equal. n_furnace = n_condenser
• When I entirely disconnect the AC the net current on the dedicated furnace line is the sum of what the average AC line reading and the average furnace line reading.

 

[UrbanFarmEngineer]

> I'd say your schematic matches your physical wiring.

Do you say that the diagram I posted is equivalent to the manufacturer' wiring?
Help me understand. I can't see that. Would the path of current flow be the same in both?

 

[Averagesupernova]

Help me understand. I can't see that. Would the path of current flow be the same in both?

I'm sorry. I can't see it for you. It doesn't matter if the part where the current 'splits' and part goes one way, part goes another way is at the molex connector or not.
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When I entirely disconnect the AC the net current on the dedicated furnace line is the sum of what the average AC line reading and the average furnace line reading.

I'm not making sense of this.
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Back to the original complaint:
With the clampmeter around the hot and neutral of the dedicated circuit feeding the furnace you claim a residual reading. Meaning the current in the hot and neutral are not identical and don't 100% cancel as they should. You claim that when turning off the main breaker to the furnace, the meter drops to zero. You have to isolate things. Did you disconnect all of the low voltage wiring that goes to the outdoor unit and check for current imbalance on the dedicated furnace circuit like I asked a month ago? If so, did you still have an imbalance?

 

[UrbanFarmEngineer]

Hey @Averagesupernova
OK ... lol you remind me of a really strict boss that once had... that's ok tho I learned a lot from him.

Sir, in response to your question and I did think that your hypothesis last night and thought it made the most sense.. however I disconnected the condenser COMPLETELY from the board and I am still getting the same results as when I run the furnace with the AC breaker switched off.

I measured the resistance values between the two condenser wires (hot and neutral) and got around 19Ohms. Someone contextualize that for me?

What next? I am following your lead.

 

[UrbanFarmEngineer]

I will add that the net current value on my ammeter really jumps when the blower fan is starting up then it jumps around a little then drops to a lower value.

 

[UrbanFarmEngineer]

I got a picture of the connector that I was talking about earlier. Hope it helps and I apologize for the poor quality:
L1 is obviously hot in
2 - goes to Molex
3 - Goes to blower fan

Zoomed out a little:

 

[UrbanFarmEngineer]

Here is a close up of the entire main board with the condenser reattached... if this helps anything at all.

 

[Averagesupernova]

I measured the resistance values between the two condenser wires (hot and neutral) and got around 19Ohms. Someone contextualize that for me?

It means nothing insofar as the imbalance issue is concerned since you said the imbalance exists with all of the outdoor unit wires disconnected.

 

[UrbanFarmEngineer]

UPDATE:
I disconnected the thermostat except the common and tested all the wires against common. No issues.

However, I noticed when I tested common to ground, which was a grounding lug in the cabinet, I got a resistance values of 0.03 Ohms. When I touch the leads together I get 0.00 Ohms

Should I not be getting 0.00 Ohms of resistance between common and ground? or at most 0.01 maybe..?

 

[Averagesupernova]

I disconnected the thermostat except the common and tested all the wires against common. No issues.

Have you disconnected the wires between the outdoor unit and the furnace? The thermostat is not a halfway point between them.

 

[UrbanFarmEngineer]

Have you disconnected the wires between the outdoor unit and the furnace? The thermostat is not a halfway point between them.

Yes I did that yesterday and reported the results. There was no change in the net current. Half of the net current just didn't flow back along the condenser line to the panel. It all went along the furnace line.

I do have a significant clue though: I opened the furnace's main ON/OFF switch today to have a look and I measured the ground wire with my ammeter and there was current!
I went back to the main panel to investigate and when I separated it out from all of the other bare ground wires that it was touching... there it was. Net current on that wire and that wire alone.

So something must be touching the chassis somewhere and spilling current which is travelling back to the panel. I am suspicious of the High Limit Switch because it plugs right into the back of the cabinet and if the prongs are bent just a little they could be touching the cabinet wall. The wiring diagram shows it's default position as closed but when I did a continuity test it showed OL.

If the current is spreading across the metallic surfaces like this it is also a good reason why it is not blowing the transformer fuse.

Any thoughts ?

 

[Tom.G]

Also this is a noob question because I don't wire things for a living... what the heck is this type of connector called because this is what I have in the place where I believe there may be that wiring error.

The style of the pins in that picture are known as "bullet", or sometimes "barrel" pins & socket.
I'm not sure what the 3-conductor female connector is called, perhaps a "splice connector" or "tap connector." For instance a 2-way or 3-way tap; perhaps even a "splitter," but splitter is unlikely because that has a different connotation.

I notice the image you posted has the manufacturers name over-printed on it, I suggest you look on the manufacturers website to find their name for the style.

The fan is always running you are right.
The fan cannot be turned off at the thermostat either.

The only way to get the fan to go off is to shut power for everything down at the thermostat.

Check the back of the thermostat for either a small switch or a jumper that can connect 2 of 3 pins. If either exist, their positions may be labelled "G" and "E", or "GAS" and "ELEC".

On a Gas furnace, their is a thermal switch in the firnace that turns the blower On when the furnace is Hot, and Off when it Cools off.

Heat Pump systems have their blower switched On and Off by the thermostat. This function is in the thermostat because the blower needs to run for both heating and cooling.

Cheers,
Tom