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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Ok so I had a question

Customer Question

Ok so I had a question
Submitted: 8 months ago.
Category: HVAC
Expert:  Rick replied 8 months ago.

What is your question?

Customer: replied 8 months ago.
I was trying to install a honeywell lyric thermostat and it didn't have a c wire so I went up to the attic and found a wire that had no designation a connected it to c and then tried connecting my thermostat I heard a buzzing sound in the attic. The thermostat didn't work and I turned off breaker . So when I tried to install the thermostat back it didn't turn on ac. I went to the attic and saw that the blade fuse was blown. I replaced it and it worked for about 5 minutes and then stopped. I went back up and the fuse was still fine...so..don't know what might of happened. When I turn the breaker on the fan outside works but the ac in the attic doesn't
Expert:  airheatman replied 8 months ago.

Can you attach a photo showing me what wire you connected to and provide model on furnace?

Customer: replied 8 months ago.
Here is a picture of the unit info and the box that says C I connected the wire to that
Expert:  airheatman replied 8 months ago.

OK if you connected the C from thermostat to that C, you sent 120 volts to the thermostat and possibly fried it.

The C,208V and 230v are high voltage connections. You would need to connect to the smaller wire on opposite side of transformer

Expert:  airheatman replied 8 months ago.

Notice in picture below.High voltage on one side of transformer.Low voltage on other

Expert:  airheatman replied 8 months ago.

Move the C wire from thermostat over to the small black and we will see if thermostat comes on or if it received damage

Customer: replied 8 months ago.
Ok the thermostat didn't have a c wire. I bought a honeywell lyric and it requires a c wire to work....my old thermostat ran on batteries so it didn't need one...so I saw a wire that didn't have a designation at the thermostat traced it up in the attic I then connected it to the c picture I sent you.
Expert:  airheatman replied 8 months ago.

I totally understand. The problem is that the C you connected to is a line voltage 120 volt wire. You can not connect there. The low voltage circuit comes off the opposite side of transformer.Your C from thermostat should connect o that small black wire , not the C you connected it to.

Customer: replied 8 months ago.
Ok I understand. What small black wire are you talking about? Another thing is that when I tried to install the old thermostat and put back everything the way it was ..ac doesn't work anymore. Condenser fan turns on out side but no air blowing in the house
Expert:  airheatman replied 8 months ago.

The small black wire beside the red one on back of transformer. If blower is not coming on you may have burned up the control board that controls the blower.The reason you popped fuse is by having R fro thermostat connected to 24v and C from thermostat connected to 120v, you created a dead short.

Customer: replied 8 months ago.
Ok so what is my next step?
Expert:  airheatman replied 8 months ago.

If you have a multi meter I can help you troubleshoot.Otherwise you will need to get a meter or call in a technician.

Customer: replied 8 months ago.
I do have a multimeter
Expert:  airheatman replied 8 months ago.

Excellent. First lets do this. Start at transformer where you connected C wire.

Check for 230v between the C and 230V

Then check for 24v on back side between Red and Black smaller wires.

Customer: replied 8 months ago.
I currently have breaker off ...do I turn it on
Expert:  airheatman replied 8 months ago.

Yes

Customer: replied 8 months ago.
Ok so when I turn breaker on ...Condenser fan turns on do I disable the fuse box near it or I leave it running during the testing
Expert:  airheatman replied 8 months ago.

If thermostat is wired, Lets makes ure it is OFF

Customer: replied 8 months ago.
Ok between the c and 230 I get 242....between c and 208 I get 218....on the back side I'm getting 28v
Expert:  airheatman replied 8 months ago.

Excellent. Now have you moved the C wire over to the small black?If not do so now

Customer: replied 8 months ago.
Better pic
Expert:  airheatman replied 8 months ago.

Thanks much better,Wire is brown instead of black, Connect C from thermostat to that brown

Customer: replied 8 months ago.
Ok so I had the black one and wrapped the wire around it and I accidentally touched the body of the furnace and their were some sparks. I now know it's the brown one and to shut off the breaker near the furnace before doing anything
Expert:  airheatman replied 8 months ago.

OK, so lets connect C from thermostat to that brown (sorry, it look black in first pic). Then let me know what you have connected at thermostat

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