Thermostat wires touched each others while the power was on

tomtomtom

Hello everyone,

The model is Carrier CA15NA036-A. The system stopped working after the wires touched.
The setup before I took them out was:
- Red wire to Rh
- Blue wire to C
- Green wire to G
- Yellow to Y/Y1
- White to W1 (AUX1)

I think the Rh and C wires touched first. G and W1 probably did as well. I am wondering how to fix it and what would be the cost? Any suggestion is greatly appreciated!

Jamie Hall

First thing I'd look at is whether I still have 24 VAC between Rh and C. If not, you probably smoked the transformer -- unless you got lucky and there is a fuse.

EdTheHeaterMan

Don't you just hate it when all the smoke comes out of those transformers

The first thing is to remove all the suspect wires from the system ... then check for 24 volts. Once that is determined, shut off the power, then use wires that have good insulation and won't have conductors touching. Wire the thermostat to the HVAC unit as directed by the wiring diagram. Once you are sure there are no touching conductors, turn on the power and check out the thermostat function. You should be just fine (as long as you did not let all the smoke out of the transformer).

Why did this happen? Were you upgrading to a smart thermostat and forgot to turn off the power?
Just a guess!

mattmia2

That looks like that is a condenser model. The transformer is in the furnace or air handler. Can you post a picture of the schematic on the cover of that?

tomtomtom

Jamie Hall said:

First thing I'd look at is whether I still have 24 VAC between Rh and C. If not, you probably smoked the transformer -- unless you got lucky and there is a fuse.

This is all new to me. Apologize for asking a very basic question but what should I buy to measure that? Thank you!

tomtomtom

EdTheHeaterMan said:

Don't you just hate it when all the smoke comes out of those transformers

The first thing is to remove all the suspect wires from the system ... then check for 24 volts. Once that is determined, shut off the power, then use wires that have good insulation and won't have conductors touching. Wire the thermostat to the HVAC unit as directed by the wiring diagram. Once you are sure there are no touching conductors, turn on the power and check out the thermostat function. You should be just fine (as long as you did not let all the smoke out of the transformer).

Why did this happen? Were you upgrading to a smart thermostat and forgot to turn off the power?
Just a guess!

I was taking the thermostat off to repaint the room. Should have moved it away from the wall

When checking for 24 volts, do you measure between each pair of wires? Thanks

tomtomtom

mattmia2 said:

That looks like that is a condenser model. The transformer is in the furnace or air handler. Can you post a picture of the schematic on the cover of that?

I assume I have to get up to the attic to get the schematic right? Will try to do that early tomorrow

HVACNUT

If the air handler is also Carrier (The model you gave was the condenser) then bring up a flashlight and a 5/16" hex driver. Turn off the power, remove the door to the blower compartment and look for a 3 or 5 amp plug in fuse, like in a car. It could be on a circuit board, or just bundled up in the wires.
Also if the wires were still attached to the thermostat while they shorted, you might need a new thermostat. 
And yes, there are much better WiFi options than Nest.

Jamie Hall

You will need a multimeter do measure the voltages. May I caution you: 24 VAC on the thermostat wires will give you a tingle. 120/240 on the power wires in the unit can kill you, so be careful.

As to what voltage one should have between various pairs of wires -- or ground -- one would need a circuit diagram. In general, however, should have 24 VAC between whatever was hooted to Rh on the thermostat and C on the thermostat. The other wires on the thermostat are switched by the thermostat, and the voltages could be pretty much anything, depending on whether they are connected at the other end and what the thermostat is doing.

STEVEusaPA

You've done enough, call a tech.

EdTheHeaterMan

I don't think this is too difficult a test. Touch the red wire to the green wire and see if the fan starts. if it does, then the transformer is still working. If it does not, then call a tech.

@STEVEusaPA might have you call a Professional Painter. What were you thinking trying such a commonplace, susceptible, and highly unskilled task as painting. Are you trying to put immigrants out of work?

tomtomtom

HVACNUT said:

If the air handler is also Carrier (The model you gave was the condenser) then bring up a flashlight and a 5/16" hex driver. Turn off the power, remove the door to the blower compartment and look for a 3 or 5 amp plug in fuse, like in a car. It could be on a circuit board, or just bundled up in the wires.
Also if the wires were still attached to the thermostat while they shorted, you might need a new thermostat. 
And yes, there are much better WiFi options than Nest.

Thank you! Everything was working fine until I dissembled the wires from the thermostat. I believe the model I have is similar to this one (gas furnace)
https://www.hvac.com/wp-content/uploads/2018/10/carrier_58CTW_installation.pdf
They suggest using only 3 amp fuse

From the PDF
The 24--v circuit contains an automotive--type, 3--amp. fuse
located on the control. Any direct shorts during installation,
service, or maintenance could cause this fuse to blow. If fuse
replacement is required, use ONLY a 3--amp. fuse of identical
size


Btw the smart thermostat is from Carrier as well

tomtomtom

Jamie Hall said:

You will need a multimeter do measure the voltages. May I caution you: 24 VAC on the thermostat wires will give you a tingle. 120/240 on the power wires in the unit can kill you, so be careful.

As to what voltage one should have between various pairs of wires -- or ground -- one would need a circuit diagram. In general, however, should have 24 VAC between whatever was hooted to Rh on the thermostat and C on the thermostat. The other wires on the thermostat are switched by the thermostat, and the voltages could be pretty much anything, depending on whether they are connected at the other end and what the thermostat is doing.

Thank you! I think I will do this and the wire touching trick that the other poster suggested to see the system starts or not

tomtomtom

STEVEusaPA said:

You've done enough, call a tech.

It's getting real hot so they are all booked up when I called to have my HVAC tuned up. I would rather fix it myself if it's not too difficult or dangerous. Thanks

tomtomtom

EdTheHeaterMan said:

I don't think this is too difficult a test. Touch the red wire to the green wire and see if the fan starts. if it does, then the transformer is still working. If it does not, then call a tech.

@STEVEusaPA might have you call a Professional Painter. What were you thinking trying such a commonplace, susceptible, and highly unskilled task as painting. Are you trying to put immigrants out of work?

Thanks I did not know this. I assume that other functions can start by touching the red wire with the yellow and white wires? Fingers crossed that the transformer is still ok

EdTheHeaterMan

Try the test I presented earlier. Touch the red and green wires together to see if there is 24 volts. The fan should run when you touch those two wires together.

Let me know if that works. I would start a private message chat with you but your profile is Private. You must start the PM when your profile is private.

tomtomtom

Here is the picture of the working system before I took it off

mattmia2

tomtomtom said:

Thanks I did not know this. I assume that other functions can start by touching the red wire with the yellow and white wires? Fingers crossed that the transformer is still ok

Don't do those at the same time. R-W will make a heat call and turn on the heat. R-Y will wurn on the condenser and maybe the fan depending on how the system control works. R-G turns on the fan and is the safest option. In the future you should turn off the switch by the furnace or the breaker for the furnace if it is in the attic before disconnecting the thermostat wires.

Be careful that the nicked insulation on the Y wire doesn't short to anything or cut it back and re-strip it.

You can cut the other wires shorter so there is less uninsulated wire outside the terminal too.

tomtomtom

EdTheHeaterMan said:

Try the test I presented earlier. Touch the red and green wires together to see if there is 24 volts. The fan should run when you touch those two wires together.

Let me know if that works. I would start a private message chat with you but your profile is Private. You must start the PM when your profile is private.

I've just removed that option. Thanks for letting me know!

tomtomtom

mattmia2 said:

tomtomtom said:

Thanks I did not know this. I assume that other functions can start by touching the red wire with the yellow and white wires? Fingers crossed that the transformer is still ok

Don't do those at the same time. R-W will make a heat call and turn on the heat. R-Y will wurn on the condenser and maybe the fan depending on how the system control works. R-G turns on the fan and is the safest option. In the future you should turn off the switch by the furnace or the breaker for the furnace if it is in the attic before disconnecting the thermostat wires.

Be careful that the nicked insulation on the Y wire doesn't short to anything or cut it back and re-strip it.

You can cut the other wires shorter so there is less uninsulated wire outside the terminal too.

Learn something new everyday. Thank you!
I am wondering if the hole in the dry wall has any impact on the thermostat?

ChrisJ

If you can get a picture of the inside of the unit where the thermostat wire goes to. Not too close, let us see the circuit board if there is one, or other wires and things in the cabinet. Take several if need be, the more details the better but make sure we can see the overall (big picture) in the end.

That may help a lot very soon.
Ed is right, but I think on my unit you have to touch RH to the G wire for a while to turn the fan on as there's a delay.

mattmia2

tomtomtom said:

I am wondering if the hole in the dry wall has any impact on the thermostat?

You should stuff some foam or something like that in the hole to keep air from moving through there. Drafts from inside the wall can affect the reading.

tomtomtom

EdTheHeaterMan said:

Try the test I presented earlier. Touch the red and green wires together to see if there is 24 volts. The fan should run when you touch those two wires together. Let me know if that works. I would start a private message chat with you but your profile is Private. You must start the PM when your profile is private.

II'm just tried touching green and red wires for 3mins but nothing moved. 0.01 V is the measurement between red and blue wires.

What would be the next steps? Thanks

tomtomtom

The face of the thermostat is completely black

HVACNUT

Did you find a fuse?

tomtomtom

HVACNUT said:

Did you find a fuse?

Yes I found the fuse at O'Reilly ($5 for 5) but it's burning hot right now in the attic. I will have to wait till tomorrow morning before heading for work. Will report back.

tomtomtom

Quick question: on the electric panel outside the a double handle with A/C letter next to it. Is that one for the furnace too?

Jamie Hall

That voltage reading between red and blue indicates that there is no power going to the thermostat. Now it might be a fuse. You can hope...

ChrisJ

Head up an hour after the sun goes down. It'll still be hot but should be tolerable.

If you wait until tomorrow you're not going to like it unless it's raining.

EdTheHeaterMan

tomtomtom said:

Quick question: on the electric panel outside the a double handle with A/C letter next to it. Is that one for the furnace too?

The Double handle circuit breaker for the Air Conditioner will operate the outdoor Unit only. If your indoor unit in the attic is for air conditioning only or if it is a heat pump then it is possible that there is a different double pole breaker for the indoor section in the attic. If it is a gas furnace then there is only a single handle breaker. You should be able to turn off the attic unit with a switch in the attic.

tomtomtom

EdTheHeaterMan said:

tomtomtom said:

Quick question: on the electric panel outside the a double handle with A/C letter next to it. Is that one for the furnace too?

The Double handle circuit breaker for the Air Conditioner will operate the outdoor Unit only. If your indoor unit in the attic is for air conditioning only or if it is a heat pump then it is possible that there is a different double pole breaker for the indoor section in the attic. If it is a gas furnace then there is only a single handle breaker. You should be able to turn off the attic unit with a switch in the attic.

Thanks @EdTheHeaterMan ! So next time before I mess around with the thermostat, I will have to go to the attic and turn the furnace off first?

109A_5

If the circuit breaker panel box is more accessible than the attic, I would identify the breaker for the furnace / air handler unit as @EdTheHeaterMan stated and shut it off there if you don't want to go into the attic in the future.

HVACNUT

tomtomtom said:

HVACNUT said:

Did you find a fuse?

Yes I found the fuse at O'Reilly ($5 for 5) but it's burning hot right now in the attic. I will have to wait till tomorrow morning before heading for work. Will report back.

I guess I should've asked "Did you find a blown fuse?" 
Before anything else, gotta see if there is one. Good thing you got 5 because without a meter its T & E.

Is this a furnace or an air handler? Does it have a flue going out the roof? If it's a furnace, there should be an emergency switch. Preferably near the attic access. 

As far as the burning hot attic? It's when you stop sweating you need to worry.

EdTheHeaterMan

This reminds me of a Dad Joke:

Three very old friends were walking down the street. First guy says What day is it? Second guy says  Thursday. Third guy says Me too, let’s go grab a beer

tomtomtom

Sucess report: after replacing the blown 3 amp fuse, the system starts working again. Thanks a lot @EdTheHeaterMan and everyone for being super helpful throughout the troubleshooting process. Have a great weekend everyone!

tomtomtom

HVACNUT said:

tomtomtom said:

HVACNUT said:

Did you find a fuse?

Yes I found the fuse at O'Reilly ($5 for 5) but it's burning hot right now in the attic. I will have to wait till tomorrow morning before heading for work. Will report back.

I guess I should've asked "Did you find a blown fuse?" 
Before anything else, gotta see if there is one. Good thing you got 5 because without a meter its T & E.

Is this a furnace or an air handler? Does it have a flue going out the roof? If it's a furnace, there should be an emergency switch. Preferably near the attic access. 

As far as the burning hot attic? It's when you stop sweating you need to worry.

It is a gas furnace model 58PHY070
https://resource.carrierenterprise.com/is/content/Watscocom/carrier_58phb070---01116_article_1428408421072_en_ss

Jamie Hall

fuses are so useful...

JakeCK

Jamie Hall said:

fuses are so useful...

Gotta love that simple itty bitty strip of metal. 

tomtomtom

The fuse on the circuit board



Close up of the blown fuse