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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22256
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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No power to red wire

This answer was rated:

No power to red wire

You likely have blown a 5 amp fuse in the air handler. Do you have access to check this with direction?


Customer: replied 3 years ago.

Yes sir! If you can tell me where it is.


The air handler has 2 with pipes entering and one that does not.

We want to remove the door without pipes....then look for a circuit board that has wires attached. If you get me the model number of the air handler I can be specific possibly with pictures.


Customer: replied 3 years ago.

aruf061-oda-1 is the model number. I have the cover off.

Thank you,

depending on age the ARUF came wired a bit different.

Does your unit have a small circuit board inside?...or can you take a pic and post?


Customer: replied 3 years ago.

Just emailed it to you.

That may take admin a while..can you post it or share it at a site like

Customer: replied 3 years ago.

Sorry...I cannot see the attachment.

Customer: replied 3 years ago.

I put it on mediafire, listed under my other email [email protected]

go to mediafire and use the share link and give me the link

Customer: replied 3 years ago.

Thank you.

Do you see the terminal marked xfrm R?

Follow that wire back to the transformer

does the red wire have a inline fuse before the it gets to the transformer?

Customer: replied 3 years ago.

No. I don't see any inline fuses anywhere.

with power on....and door safety switch taped down (if present)

Use meter and test terminals XFRM R and XFRM C

tell me 24v present. If this is an older unit it may not have fuse protection...this would mean bad transformer. But this will test that theory

Customer: replied 3 years ago.

Any other way to test it? I don't have a meter with me. But if there are no fuses and no power at thermostat, it's probably the transformer, right?


That is correct providing:

The unit still has main power.

The number 1 fault that occurs when changing thermostat is a low voltage short. Which when low voltage fuse is present it blows. In the absense of a low voltage fuse it burns out the transformer.


Customer: replied 3 years ago.

Can you tell by looking at it (after removing it) if it's blown? Also, can I buy a transformer at Lowes or Home Depot?

This particular unit needs a 208/230 - 24v 40va transformer.


I have never attempted to acquire from home improvement store.


Customer: replied 3 years ago.

Maybe an electrical supply store? No way to tell it it's blown after taken it out?


The only way is to apply 220 volt to the input...if no 24v at output then transformer is bad. They usually smell acrid if bad.

An electrical supply would carry this.

Customer: replied 3 years ago.

Thank you. Looks like my electrical supply place is close for Labor Day. Bad day to screw up my HVAC. Thanks for the help.

I really wish you well.

If you need further help just let me know.


Customer: replied 3 years ago.

Thanks so much for your help. Best wishes to you also.

I apologize but if not rated this keeps requesting a response/rating.

If satisfied - rate
If not satisfied disregard and do not respond

Have a great evening


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