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No power to tstat, I've flipped breakers off / on at power…

Customer Question
No power to tstat...

No power to tstat, I've flipped breakers off / on at power box, at air handler and pulled and placed back the shut off outside at compressor. Checked fuse inside air handler, still no power on R on thermostat. Carrier a/c system Air handler model FY4ANF048T00

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

digital thermostat, no power no nothing

Contractor's Assistant: Do you plan on doing the work yourself?

Yes if its minor

Contractor's Assistant: Anything else we should know to help you best?

Thats it

Submitted: 6 months ago.Category: HVAC
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Answered in 4 minutes by:
12/23/2017
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago
BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 23,122
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Verified

Hello, my name is Billy,

What function have you been using recently?..heating or cooling?

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Customer reply replied 6 months ago
cooling, I live in FL
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

thank you.

There is a safety switch on most units that turn off power to the thermostat if the drain gets plugged. Is your air handler in the attic?

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Customer reply replied 6 months ago
In the garage. pan completely dry. I don't think the float switch has ever been activated. I push it up and it came back freely
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

Are you willing to remove the cover over the wiring area of the air handler to see if there is a control fuse present?

was thermostat recently changed?

any recent yard work around the outdoor unit?

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Customer reply replied 6 months ago
i have the cover off. pulled out atc fuse and it looks ok. I haven't changed anything on the system. tstat is 24 volt wired to air handler. put volt meter on R pin and C and got 0 volts on tstat
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

do you have 24 volts at R and C in the air handler?

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HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

Or even back up...do you have 220v to the transformer

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Customer reply replied 6 months ago
can you get me a parts breakdown to help me identify. I got 230 in and out of the breaker inside the air handler. Then I got 230 to the rectifier control. It goes to what I believe is the 24 volt transformer. On the bottom I have 230 terminal and common. I got 0 between those terminals. I get 230 if I go from the 230 terminal to the ground wires at the breaker. I have a red and brown wire that comes out at the top. I think this is the power for the thermostat. I got 0 between these terminals.
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

Ok this shows a bad transformer.

230 input to transformer an d zero out = bad 24v transformer. The transformer is known as a generic part as any 230 to 24v transformer will work. Just google the number on side of the transformer to obtain parts availability

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Customer reply replied 6 months ago
I'm not sure. I got 230 when grounding to the incoming ground wire at the breaker. I got 0 between the 230 and Common terminal on the bottom. Is this the ground going in to the transformer? I might not be testing properly. The only way I get 230 is when I ground to the incoming wire at the breaker?
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

ok, take a pic and post of the wiring area and I will draw test points for you.

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HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

put meter leads as shown HERE and tell me what value

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Customer reply replied 6 months ago
0
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

ok now can you show me the contact point where the 2 power wires come into unit?

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HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

we are missing one leg at the transformer...that is why we need to back track right now

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Customer reply replied 6 months ago
OK, but I do get 230 if I ground that terminal to the incoming nuetral wire in the last photo its the white wire with red tape on it
IMG_6134.JPGIMG_6134.JPGIMG_6138 (1).JPGIMG_613...JPGIMG_6137.JPGIMG_6137.JPGIMG_6135 (1).JPGIMG_613...JPG
Customer reply replied 6 months ago
Billy, I'm no expert but I believe that is the transformer. I don't think the C is for common. I got 120 volts on the yellow wire terminal grounded to case and 120 volts on the black wire when grounded to case. I got nothing on what I believe is the 24 volt terminals at the top, jumping the red and brown wires.
Customer reply replied 6 months ago
it looks like both heating elements have the black and yellow wires going to each of them. I can ground them and I get 120volts out of each of them.
Customer reply replied 6 months ago
the incoming power goes through a breaker. If I jump between the 2 incoming wires I get 240 volts. If I jump between the 2 out going wires I get nothing. I can ground the out going wires and get 120 volts on each. Could I possibly have a bad breaker?
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 6 months ago

you are correct...it appears to be a bad connection or breaker....the 120v you are reading is the same 120v everyplace...we are missing the other 120v.

That is why we have 230 at incoming breaker and not leaving

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