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Hot Topics: Problems with Oven Fuse

The forums have conversations between more than 250,000 experts and beginners in over 120 categories, so during the week we will mark a conversation that can help with your next project. This transcript has been easily edited.

Original post: Carrier-packed heat pump: can't find the 3 amp fuse

dogdodge – Member


I am a new homeowner and was trying to change my thermostat. I released my switch labeled AC but when I went to disconnect the wiring it went out. I turned off my head and switched everything exactly the same (according to pictures) and now have no power.

My AC unit is an older carrier model: 50yq030300 ser: w1

15200. I have already changed the disconnect fuses but cannot find a circuit board or the small 3-fuse to check if it has blown. My thermostat is battery powered but will not receive any power and will not turn on my AC as before.

Any help would be greatly appreciated.

Further details: [19659005] Heat pump

Rooftop Unit

Replace both switches for the heat pump and the AC unit with 30 amps.

I have pictures of where the wiring is connected to the roof unit and further pictures of the main plate and the interior of electrical components.

PJmax Group Moderator

Welcome to the forums.

Unfortunately, there is not usually a fuse in an old packaged unit. Go to the area where the low voltage controls are. Find the transformer. It may have a fuse in one of its secondary wires. If not ….. more than likely the transformer is blown. There should be a wiring diagram on the service door. A fuse …. if there was one …. should be shown on it.

Carrier 50YQ manual (pdf)

dogdodge Thread Starter ]

Hi Pete,

Thanks so much for your answer ! I had been looking for that manual for hours but had no luck.

I have also attached the photos. Do you think changing the transformer is something that a DIY can do?

I found this site that says it has the transformer.

I also found this page that seems to list the parts but has no transformer but is for the exact model of the package.

  thermostat cables

  old thermostat cables

  thermostat cable panel with arrow pointing to piece

  oven model information

  electric oven model information

roughneck77 – Member

The transformers in the last photo of the timer. [19659005] Does not look like it has current protection. You can test it with your meter to see if it works or not.

PJmax – Group Moderator

You do not need to use the same exact transformer. You need a 24VAC 40VA – 240VAC in.

Most replacement transformers will be 120/208 / 240VAC in. That's good. You should only use 240v.

Replacement transformer

I put an arrow in the picture. There will be two wires on each side of the transformer. Two wires are 240V IN and two wires 24V OUT. More than likely you will miss the 24v side.

dogdodge Thread Starter

Thanks Pete and Roughneck. I will take a closer look at the part you marked and order the transformer and try to replace myself. I will report back when I have done so.

Thanks so much for your help with this !! I would really be lost without this.

roughneck77 Member

Get a transformer with a built-in switch, or install an inline fuse for future protection.

PJmax Group moderator

I think the circuit breaker only comes in the mega transformers …. like 80va.

A fuse and fuse from a car dealership would be a good choice.

Use 3A or 4A ATC fuses ….. same as a car.

  a small fuse with wires

roughneck77 – Member

You can get them in the smaller versions. I have a 40 vA with an internal switch with me now.

dogdodge – Thread Starter

Hello everyone,

It was the transformer and I installed an inline fuse. Thanks so much for your help with this !! Really saved me. Especially PJMaxx!

PJmax Group Moderator

Good job. Thanks for knowing how you did it.

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