Question about Heating & Cooling
I replaced my thermostat last night with a Honeywell RTH7500D without turning the power off, and it is no longer working. From what I have read I may have shorted out the transformer, how do I tell if this is the issue?
Check for 24 volts ac at R & C terminals at the t-stat. Your transformer will have 4 wires hooked up to it. Two on one side and two on the other. Two of them will read either 120v or 240 v ac depending on whether you have a 120 or 240 v voltage. The other side should read 24 volts. If you are not reading 24 volts, then you have burnt the transformer and will need to replace it. If you are reading 24 volts, check to see if there a low voltage fuse located on the control circuit board or somewhere between the transformer and "R" terminal.
Here's a picture of a typical low voltage transformer found in an A/C system:
If you replace the transformer, add a 5 amp fuse on one of the 24 volt leads......this will save you from having to replace another transformer in the event of future "short" in the low voltage circuit.
Contact me with any questions or concerns.
I hope you find this to be very helpful to you moving forward,
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Posted on May 09, 2010
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Posted on Jan 02, 2017
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