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The 3 amp fuse blew up when calling for heat When disconnect…

Customer Question
Hello The 3 amp fuse blew...
Hello
The 3 amp fuse blew up when calling for heat
When disconnect the pressure valve tube the flue fan works but when connecting the limit sensors the fuse blew even when disconnecting the gas valve output
When calling for heat the fan comes on after few minutes and the flue fan run but once connecting the limit switches wire the fuse blew
Even when i bypass the limit sinsors and connect the in and out wires for limi sensor and disconnect the gas valve wire the fuse blow out
Submitted: 8 months ago.Category: HVAC
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Answered in 14 minutes by:
11/17/2017
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago
Gaztech
Gaztech, HVAC Technician
Category: HVAC
Satisfied Customers: 922
Experience: Owner at Gaztech
Verified

Hi I amCustomer a independent technician, I will assist you with your issue.

Don't forget to rate the 5 star rating AT THE TOP OF PAGE after we are done. this will credit me for assisting you.

Is the fuse burning ever since you replaced the new board, is it possible your wiring is wrong?

It is clear that you have a short with the limit sensor circuit, inspect all wiring and sensors,

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Customer reply replied 8 months ago
Thank you
It keeps blowing
I bypassed all sensors and connect the in and out of The limit switch and is still burning the fuse
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

Is the fuse burning ever since you replaced the new board, is it possible your wiring is wrong?

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Customer reply replied 8 months ago
This is the board and the low voltage socket has 5 wires in and out to pressure switch and in and out to all limit switches and out for valve
If I break the limit switches crircuit the fuse stays and even whe I disconnect the gas valve wire and connect the in and out for limt switches directly and bypassing all switches the fuse blew .
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

Again!!!

Is the fuse burning ever since you replaced the new board, is it possible your wiring is wrong?

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Customer reply replied 8 months ago
keep blowing
Are you talking about the low voltage
The low voltage has only 5 wires coming in and out of the socket and I did not change the socket or the wires so the go to the correct locations and also what will make the fuse blow once i bypass the limit switchs with a clean wire to make sure it is not touching a ground
Do you think any of the high voltage might be a reason
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

I am thinking that you got a defective board with internal short.

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Customer reply replied 8 months ago
That is what I thought and i changed it twice
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

.

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HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

OK, Then a close inspection of all wiring (burnt wire touching to ground)

Follow wiring diagram to all components for possible error.

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Customer reply replied 8 months ago
Is this for the low-voltage or for the high-voltage or for both because in the low-voltage iPod I passed all the hits limit switches so I have a very clean wire connecting directly and also for the power out for the van I disconnect it so it is a small wire and I was trying to measure if I am getting power from it out the problem is once i Connect the in and outs for the limit to switch the fuse blow up
Customer reply replied 8 months ago
Is there any low voltage out of the board other than to the gas valve
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

Yes,

  1. Limit switchs
  2. pressure switch
  3. thermostat
  4. outdoor AC contactor relay
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Customer reply replied 8 months ago
The cooling works fine
The pressure switch works fine and send signal but once the limit switches cuirct closes the fuse go out even when the wire to the valve was disconnected
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago
OK, Then a close inspection of all wiring (burnt wire touching to ground)Follow wiring diagram to all components for possible error.
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Customer reply replied 8 months ago
There is no too many low voltage wires to inspect because the pressure switch works fine the limit wires are eliminated and i bypass all of the with a short wire and I disconnect the gas valve wire right after the control board
Does high voltage has anything to do with this
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago
No.
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Customer reply replied 8 months ago
When bypassing all limit switches by connecting the in and out wire will this creatute the short cuircit or these are just switches with no resistance
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

They are just on off switchs, no load, but may have resistance if contacts are dirty.

Load components are gas valve, and relays

Just by chance, try disconnecting control wires that go to AC or heatpump if you have that.

Y , C, O, R terminal on control board of furnace.

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Customer reply replied 8 months ago
The ac low voltage go directly from the thermostat to the AC unit
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

AC, OK forget that.

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HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

I think that you did not find a shorted wire or component, using a ohm meter should help you find it if you are familiar with diagnostic proceedures.

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Customer reply replied 8 months ago
What should i check with the ohm meter
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

All wiring and components, if you are familiar with diagnostic proceedures. I am sure you can find many videos on youtube to teach you how.

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HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

I noticed question is still open, rate the 5 star rating AT THE TOP OF PAGE if we are done. this will credit me for assisting you.

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Customer reply replied 8 months ago
Do you mean low voltage wires
HVAC Technician: Gaztech, HVAC Technician replied 8 months ago

Yes

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