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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 945
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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I installed a new thermostat with the help of honeywell

Customer Question

I installed a new thermostat with the help of honeywell technical support and now my new one isn't working, they think it might be a blow fuse in the air handler. I have attached pics of the thermostat before, after, air handler model, inside. I tested the continuity of the 3a fuse you see and it tested fine. I'm at a loss of what could be wrong and why I am not getting 24v to the thermostat.
Submitted: 2 months ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 months ago.

Hi I'm Brian and I'll be happy to help with this!

Do you have a voltmeter and are you comfortable to probe for 24 volts ac on the EBTDR board on your air handler? If so, with power on to your air handler and the blower panel removed to access your board, probe between the C and R points on the board without disconnecting any wires (diagram shows blue and red wires connected there) and tell me if you have ~24Vac or not.

Expert:  Brian HVAC Guy replied 2 months ago.

Also probe between XFMR-R and XFMR-C and tell me what you get.

Customer: replied 2 months ago.
Wouldn't probing the wire from the board be the same as probing the wire on the wall? the previous thermostat worked just fine, I think I tripped a breaker/fuse somewhere in the air handler (I accidentally did this at my previous house a few weeks back before a move, flagged down a HVAC guy and he helped me out). And no prob going to prob, comfortable doing that, but which diagram are you looking at? I prob should upload better quality pics, right?
Expert:  Brian HVAC Guy replied 2 months ago.

I am using your diagram for color codes. I am using a picture of your board from the Goodman website for probe point designators. Better pics would be good, I can actually annotate them and point to the probe points. If your particular heater accessory has the circuit breaker option(s) in it, then you should shut them all the way off then turn them all the way on again. The points on the board at C and R are 24 volts after the fuse for use by your system and XFMR-C and XFMR-R on the board are before the fuse directly off of the 24 volt transformer.

I just want to see if you have ~24Vac everywhere (or anywhere) you're supposed to. If don't have 24 volts between XFMR-C and XFMR-R and you're comfortable probing high voltages, you can probe between the larger Red/Red and Black/Purple wire connections at the transformer. If you have 240 volts going into the transformer but don't have it coming out of the transformer between XFMR-C and XFMR-R on the board then you have a blown 24 volt transformer.

If you're not sure of any of my test procedures, send a pic and I'll mock it up.

Customer: replied 2 months ago.
Ok will send better pics shortly
Expert:  Brian HVAC Guy replied 2 months ago.

Sounds good... standing by...