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Phil, Mechanical Engineer
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Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I was installing a new Nest Learning thermostat. I received

Customer Question

I was installing a new Nest Learning thermostat. I received an error code that signified that I wasn't receiving any power to the unit. I then went upstairs and realized that my upstairs thermostat is not receiving power either. I figure I blew a fuse. I went upstairs and I have a Honeywell Dual Zone controller. Is there a way I can reset that fuse? Thank you. Erik
Submitted: 11 months ago.
Category: HVAC
Expert:  airheatman replied 11 months ago.

Eric I am not sure you can use the Nest with a zone system, Do you want to try to see if we can find the fuse so you can reconnect old thermosat? If so give me model on your air handler/furnace.

Customer: replied 11 months ago.
I am confident I can use the Nest with a zone system. I confirmed that before the purchase. Plus, I see that confirmed everywhere online. I will head into the attic to get you the model number. Stay tuned...
Expert:  airheatman replied 11 months ago.

OK, The only problem people usually run into trying to use the Nest with a zoned system is that often zone dampers are controlled by transformers independent of the furnace transformer.In that case you are sending power from the furnace transformer on one wire and common to zone damper from a different transformer.

Customer: replied 11 months ago.
It is a Honeywell EMM-3 Electronic MiniZone Panel.
Expert:  airheatman replied 11 months ago.

What is model on furnace or air handler that thermostat controls?

Customer: replied 11 months ago.
I cannot find the furnace model, it is a Bryant. I have attached a photo...
Customer: replied 11 months ago.
Since there is no power to my existing thermostat, doesn't that mean the panel is what is the problem? The Honeywell...
Customer: replied 11 months ago.
No power to this thing...
Customer: replied 11 months ago.
Think the problem lives inside this...
Expert:  airheatman replied 11 months ago.

Remove front panel on furnace and look inside for a control board and see if there is a small automotive fuse on board

Customer: replied 11 months ago.
Here's a picture...help me locate the fuse...
Expert:  airheatman replied 11 months ago.

Probably in lower panel

Customer: replied 11 months ago.
Removed that panel and this is what is inside...
Customer: replied 11 months ago.
Here is the fuse, how do I tell if it is bad?
Expert:  airheatman replied 11 months ago.

Check this fuse.See if blown

http://i.imgur.com/kYe4Epz.png

Customer: replied 11 months ago.
Pulled it out...
Expert:  airheatman replied 11 months ago.

That does not look blown. Put it back. Next tell me where that board zone is getting low voltage to these terminals.

Customer: replied 11 months ago.
I can tell my fuse doesn't look like the fuse that you said that was blown because the wire in the middle is clean, but look at the upper left-hand corner of this picture and see that black spot, is that something I should be concerned about?
Customer: replied 11 months ago.
The board zone gets power from here...
Customer: replied 11 months ago.
Is that what you were asking in your last post?
Expert:  airheatman replied 11 months ago.

I did not ay fuse WAS definitely blown,I said it may be and we should start there. I do not think this fuse is the issue. Do you have a volt meter to see if that little plug in transformer is sending 24v to zone board?

Customer: replied 11 months ago.
I don't have a volt meter, but should I just plug something else in to see if it is working?
Expert:  airheatman replied 11 months ago.

Do you have anything else that operates on 24 volts? You can plug something into plug to make sure plug is working but that will not tell us if you fried the little plug in transformer

Customer: replied 11 months ago.
Plug works.If I can get a volt meter from a neighbor, what do I do with it?
Expert:  airheatman replied 11 months ago.

Check between those two terminals for voltage

Customer: replied 11 months ago.
Neighbor has one. So when I get back with it, just insert the meter into those two holes?
Expert:  airheatman replied 11 months ago.

Yes on those two wires we should get 24 volts

Customer: replied 11 months ago.
Give me about 5-10 minutes...stay tuned...
Expert:  airheatman replied 11 months ago.

Standing by

Customer: replied 11 months ago.
I'm back with the volt meter. Do I remove the wires and test in the holes? Simply touch the wires while in the holes? Sorry for the basic question...
Expert:  airheatman replied 11 months ago.

Leave wires connected

Customer: replied 11 months ago.
If this looks right (see attached photo), I am not getting anything in the meter...
Expert:  airheatman replied 11 months ago.

You should be getting 24 volts there,If not you probably fried that little plug in transformer. When connecting the nest did you allow wires to touch while they were disconnected?

Customer: replied 11 months ago.
When you say plug in transformer, do you mean the Honeywell MiniZone device I just used the volt meter on?Maybe on the wires touching, but I had the breaker off to the HVAC...
Expert:  airheatman replied 11 months ago.

The little transformer that supplies power to zone panel is what I am referring to.Did you have power off to it when changing thermostat?

Expert:  airheatman replied 11 months ago.

This one

Customer: replied 11 months ago.
I only had the HVAC off, not my plugs, never thought of that...Any way to test the transformer?If it is that, do they have those at Home Depot?
Expert:  airheatman replied 11 months ago.

You have just tested it, You determined that the plug is hot by plugging something else in.You determined it is not sending 24v out to board with meter. Home depot may have these as they are pretty common transformers.

Customer: replied 11 months ago.
Great. Is it possible the actual board is fried or does that not happen?
Expert:  airheatman replied 11 months ago.

It is possible, but lets hope not

Customer: replied 11 months ago.
Okay, Home Depot is closed. I will go first thing. Would it be okay to pick this up tomorrow if that doesn't work or do we close out now?
Expert:  airheatman replied 11 months ago.

Lets wait until we get finished.Tomorrow is fine.

Customer: replied 11 months ago.
Thank you sir. I appreciate it.
Expert:  airheatman replied 11 months ago.

Talk to you then.

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