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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I shorted an HVAC system by not using the circuit breaker on

Customer Question

I shorted an HVAC system by not using the circuit breaker on a thermostat switch. Need to figure out if I can do a replace of something (this time with power off) or need an HVAC appointment
JA: Thanks. Can you give me any more details about your issue?
Customer: Im a house renter. Was switching back to the old thermostat from the Nest that I was using. I think I hit the Red wire to something else. Now the system doesn't work. I went into the attic and did some basic multimeter checks for voltage, but not continuity on the honeywell controll board.
JA: OK got it. Last thing — HVAC Technicians generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
I'll have to do this this evening when I have access to the unit.
I do have a multimeter.When reattaching the thermostat, the red wire was sparking and then it stopped, so I'm sure I shorted it.
I checked voltages across the terminals on the thermostat and there was no 24v DC.I went into the attic where the furnace and blower motor is.
The left side of the unit had a motor looking thing with copper coils. There was obviously an igniter and 4 gas burners (off).The right side of the unit had the control board. It looked like the attached image (although this is not a photo from there).
The red dipswitches were on the bottom right and the bank of terminals was to the right. (so turn the image 90 degrees)I didn't get any voltage on those terminalsOut of the left side of the board, were 4 wires going to, what I presume is a transformer. The transformer had two wires on top (purple/brown and white, if I remember) to a side that I think was 115v AC. And then the other two wires came out of it and it was marked 24v. The 24 v side had 'open' terminals that I could probe directly and it was no voltage. The transformer was not hot. I removed the sleeved connectors off the input side and did a voltage check across those with the multimeter and there was no AC current (power was on, but I was being more careful).
Expert:  Rick replied 1 year ago.

What is the brand and model number of this unit?

Customer: replied 1 year ago.
figured it out. transformer
Expert:  Rick replied 1 year ago.

Ok, glad you figured it out