HVAC Electrical Issue: Current Leakage from Furnace

[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.
-
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

 

[Averagesupernova]

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.

Well in the past you have said you have had the imbalance without including the ground wire. Now you say you have current on the ground wire. Is this current still there when you turn the breaker feeding the furnace to off? In the past you've said the imbalance went away when turning the breaker off. This on/off switch you refer to, I assume it is mounted on the furnace. Do you still have ground current after shutting it off?
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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.

Concerning the above, it makes no sense. For several reasons. Both paragraphs together contradict each other. Also, according to the diagram you drew as well as the diagram from the furnace, if the circuit to the furnace is live, the blower will run. Nothing from the thermostat should be able to shut it off.

 

[UrbanFarmEngineer]

Yes I just discovered the current on the ground wire today when I opened the ON/Off switch. I hadn't known about it before. The main ground wire is from the main line and it is wound really tight inside so I couldn't get at it (and never thought about it either). The switch is mounted to the ceiling on a piece of wood. I just replaced the parts and it did not make a difference.

About the fan, when I set the thermostat to OFF the fan powers off. The fan runs constantly on Heat or Cool. I have no control over the speed and FAN setting does not work, I.e., I can't put the FAN on via the thermostat.

 

[UrbanFarmEngineer]

and no ground current after turning the switch off.

 

[Averagesupernova]

Ok. Well something doesn't add up if you can control the fan from the thermostat but that shouldn't change the current imbalance issue. I assume the imbalance current is close to the same as the ground current. Can't expect them to be identical as there could be other paths back besides the ground wire. If you suspect the blower motor, which you have in the past, wrap the clampmeter around both the hot and neutral feeding the blower motor. Only those two. Watch for an imbalance.

 

[Averagesupernova]

One other thing. Your diagram shows a block that all the neutrals connect to. This cannot be connected to the chassis. If it is this would explain your imbalance.

 

[berkeman]

Thread is closed temporarily for Moderation...

 

[berkeman]

After re-reading all 3 pages of this thread, I'm going to leave it closed. It is just too difficult to try to diagnose something like this long-distance over the Internet.

@UrbanFarmEngineer -- Please try to find an EE or HVAC service professional in your area to help you figure out these issues.

EDIT -- Thread reopened temporarily for summary post by OP.

 

[UrbanFarmEngineer]

Hey Everyone:

Thank you to all who commented on the original post with how to help. I thought you may be interested in knowing how it all turned out.

It took me a while to wrap my mind around what you guys were telling me but I am happy to report that the issues are diagnosed and solved. I got lots of good advice from all of your posts and from your PMs. In addition: I got two amazing book recommendations earlier today that I am looking forward to diving into to establish a foundation in the principles of electrical circuits so I can better keep up with what you are talking about because as terrible as the furnace experience has been it made me love learning about circuits.

So here is what's going on with the furnace:

1) Open/Faulty Limit Switch: and it's the kind that can't be reset manually. This was disovered thanks to the person who recommended I do dead testing which was @Guineafowl and I believe @Averagesupernova

2) Short to Ground in the wires leading back from the blower fan: they were not bundled/protected properly and kept rubbing up against a somewhat sharp piece of metal that extends out from the blower fan housing for some reason. A few of wires had scrapes in the insulation and exposed copper. Thank you to the people who PMd me to do visual inspections of the wires after a load and not before, since everything was still working.

3) Unprotected Power Line: Flexible cord from condensate pump inserted into same wire access point as main power line (BX). There was an AntiShort on the BX that protected the main power line conductors but the sharp side where the BX was cut sliced into the condensate power line and gouged right into the conductors. It's hard to see in the pics but you could see copper.

At Present: net current on dedicated main power line to furnace = 0 mA. Mission Accomplished.

Why did I try to fix it myself? When the local gasCo gave me notice of two electrical infraction and I called the installers they came to do an electrical diagnostic and repair. They showed up with no multimeter, no instruments of any sort. Not even a visual inspection. They did not even open the jBox behind the cords entering the cabinet in the picture below to examine the black cord which is visibly damaged! The guy just put a piece of tape over it from the outside and said, "furnace runs, means there is nothing wrong.". And there was nothing that I could say to him to make him do anything more. He just got really mad.

Researched installation company: No natural gas licence, not affiliated with any sort of electrical licence, no permit applied for when they installed the furnace (which was less than a year ago).

INSTALLERS' SOLUTION TO SHORT TO GROUND INFRACTION:

A little blurred:

 

[Guineafowl]

Shows the value of a good visual inspection (with power off!)

Or, “more is missed by not looking, than not knowing”.

I’ve found that sort of fault before by running an IR test, and watching the display as I wiggle wires, focusing on entry glands and contact points.

 

[berkeman]

Thread is reclosed.