Image 1015 is your low voltage transformer.
This circuit is rarely fused.
Check to see that there is 24VAC (more-or-less) on the secondary side of it. CAREFUL - there is 120V on the primary side!
Picure 1015 is the transformer. Should have 120 volts going in, 24 on the secondary. Terminal R (possibly RH) should have 24 volts at your thermostat.
You say you changed stats. Did the old stat have 24 volts to it? Did you turn off the power when you changed stats? I wonder if you shorted something if you did not turn off the power.
See if the primary side of the transformer has 120 volts. If not, look for a circuit breaker (and possibly) a fuse.
If it has 120 volts, see if you have 24 at the secondary. If you do, then look for something open between the transformer and the stat. If you do NOT, then likely the transformer is burned up.
So While I had flipped the switch on my circuit breaker that said Heater I did not test the power with my voltage reader to ensure it was in fact the furnace’s circuit. In fact it was not and I discovered that when I got a shocking surprise :smack: while initially getting into the furnace. So I’m not positive but odds are I did short something out when I changed the thermostat. SO… I tested the transformer, it read right around 120v when I touched the point 3 and the furnace housing. I got nothing from the others while touching any point and the furnace housing. I’m not a super electric savvy, as is obvious with my electrocution, but here is what I have done. I did a resistance test and found the following that hopefully provides some needed info to confirm the transformer is fried.
Set reader to 2k Ohm
is no contact/resistant
.000 perfect is no resistance
(yes you probably know this but I don’t know all the different voltage testers so I figured I clarify in case.
Tested this while still hooked up and again after removing the transformer from the furnace and yes this time I made sure there was NO power to the unit.
1&2 = 1. 1&3 = 1. 1&4 = 1. 1&5 = 1.
2&3 = .014 2&4 = 1. 2&5 = 1.
3&4 = 1. 3&5 = 1.
4&5 = .000
If it comes to it I’ll call an HVAC tech, but I really want to learn about this. I like knowing how my equipment works and what it takes to troubleshoot/fix if possible.
Of course this means still no heat. I do have 2 identical units in my house so the downstairs unit is making up for the attic unit, sort of.
Another thought, should I test the transformer by sticking it in the downstairs unit? Is that safe? Or use the downstairs transformer to test the attic unit?
Repeated voltage readings and Ohm test on downstairs unit’s transformer. Voltage reading gave the exact same results so I’m guessing I’m doing the 24v output test incorrectly. During the Ohms test the only difference I saw was
Looking at the picture the high side of the transformer is 240 volts.
Take a voltage between #1 and #3 it should 240 volts.
Take a reading between #4 and #5 it should be 24 volts
If you do not get 240 at #1 and #3. Take a voltage between #1 and ground and #3 and ground. (furnace case)
First find the proper breaker for the furnace. If the transformer is a 240 volts then the breaker should be a two pole breaker.
If you got 0 between 1&3 and 120 from 1 and/or 3 to round then you are ;loosing one power leg between breaker and furnace.
Safest to call an electrician or AC guy.
If you got 240 between #1 & #3 but 0 between #4 & #5 the transformer is shot.
Yeah, if you have zero resistance between 4 and 5, the secondary is shorted. That’s why I asked you to see if there is 24 volts there when you know for sure that you have 120 (or whatever your primary voltage is) going in.
In other words, if you have the proper voltage on the primary, you should have 24 volts on the secondary. If the secondary is shorted, (essentially now just one thick wire with the insulation burned off of it,) there will be no output so therefore no 24 volts to your thermostat.
The picture of the transformer you posted (is that your actual transformer?) shows a primary of 208/240 SO BE VERY CAREFUL WORKING AROUND THAT! I wanted you to check that you had primary voltage, and if so whether you then had secondary voltage. But with no resistance on the secondary I think the transformer is shorted.
**For your own safety I think you need to call someone in. **Tell them you changed the thermostat and possibly shorted the control transformer while doing so.
You are correct, I was receiving 240v when testing 1&3 and 0 volts on 4&5 in the attic.
Tested the downstairs transformer, 240v and 24v. Placed the downstairs transformer in the attic furnace it started functioning properly. It must have shorted out when I replaced the thermostat. Thats what I get for trusting the circuit board labels in a house I only bought 4 months ago. Next time I’ll ensure power is cut using my current detector pen and/or voltage reader.
Thank you very much for the information.
This time I cut the power using the t-handle disconnect box. So there will be no more surprises when I am working with it.
Now I just need to buy the replacement for my transformer.
Glad you figured it out.
Any HVAC house will have a replacement transformer, especially if you are willing to take one that doesn’t mount exactly the same as the original.
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