How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Gaztech Your Own Question
Gaztech
Gaztech, HVAC Technician
Category: HVAC
Satisfied Customers: 1020
Experience:  Owner at Gaztech
92290868
Type Your HVAC Question Here...
Gaztech is online now
A new question is answered every 9 seconds

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

Customer Question

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: 1 year ago.
Category: HVAC
Expert:  Gaztech replied 1 year ago.

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,

Customer: replied 1 year 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
Expert:  Gaztech replied 1 year ago.

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

Customer: replied 1 year 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 .
Expert:  Gaztech replied 1 year ago.

Again!!!

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

Customer: replied 1 year 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
Expert:  Gaztech replied 1 year ago.

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

Customer: replied 1 year ago.
That is what I thought and i changed it twice
Expert:  Gaztech replied 1 year ago.

.

Expert:  Gaztech replied 1 year ago.

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

Follow wiring diagram to all components for possible error.

Customer: replied 1 year 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: replied 1 year ago.
Is there any low voltage out of the board other than to the gas valve
Expert:  Gaztech replied 1 year ago.

Yes,

  1. Limit switchs
  2. pressure switch
  3. thermostat
  4. outdoor AC contactor relay
Customer: replied 1 year 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
Expert:  Gaztech replied 1 year ago.
OK, Then a close inspection of all wiring (burnt wire touching to ground)Follow wiring diagram to all components for possible error.
Customer: replied 1 year 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
Expert:  Gaztech replied 1 year ago.
No.
Customer: replied 1 year 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
Expert:  Gaztech replied 1 year 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.

Customer: replied 1 year ago.
The ac low voltage go directly from the thermostat to the AC unit
Expert:  Gaztech replied 1 year ago.

AC, OK forget that.

Expert:  Gaztech replied 1 year 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.

Customer: replied 1 year ago.
What should i check with the ohm meter
Expert:  Gaztech replied 1 year 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.

Expert:  Gaztech replied 1 year 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.

Customer: replied 1 year ago.
Do you mean low voltage wires
Expert:  Gaztech replied 1 year ago.

Yes