3 amp fuse on York Diamond 80 Furnace Blown twice

[ccmulder]

I live in California in an area that doesn't really need A/C so all I have is a gas furnace for heat (York Diamond 80).  Heat worked fine last winter and never used the unit at all from about June to October and then when I tried turning it on in October got nothing.  Checked it and the 3 amp fuse in the control board area was blown.  I replaced that but got nothing so I turned an "on/off" switch in the unit to off and back on and still nothing, then jumped the heat and power and it turned on.  Removed the "jump" and thermostat operated it fine.  Not sure but my guess is something had to "reset" for it to work.  

So it worked fine for about two months than last night we had a rain storm and had one or two instances of the lights dimming for a split second.  Woke up in the morning and no heat and not really sure when it went out.  Anyway same 3 amp fuse blown so I repeat the process and its working fine again.  But I guess the point is if that fuse blew twice now is there another issue or is it just a power surge?  Should I put in a power strip to plug into instead of directly from outlet to furnace?  Should I wait to see if it happens again? Should I change it to a 5 amp?  

[J5*]

did the lights dim because the fuse blew, or did the lights dim because you have a power drop  ?

 

it might be a case that the 3amp fuse is borderline and a voltage drop with give a current increase and might be just pushing it 

over the edge 

5amp could be an option

a 3amp slow blow might be a better option ?

can you see in the fuse ? is it just open or has it blown big time ? this is a hint of which way you would proceed 

 

[Samurai Appliance Repair Man]

Topic moved to HVAC forum. 

[alamo1718]

You most likely have a low voltage, control circuit, short. Intermittent shorts can be hard to find.  I wouldn't change to a 5 amp. This unit is pretty straightforward and when it's functioning correctly shouldn't pull anywhere near 3 amps on the thermostat wires.If you change to a 5 amp, the problem might damage other components, i.e. transformer or board itself.  Look for wire rubs, where a wire is rubbing against something and shorting out. Visually look at every inch of every thermostat wire. The last one I found was rubbing on the outdoor unit, under the fan, fan motor and rubbing on the refrigerant line itself. I read that you have no A/C so this isn't your issue but just illustrating that it can be hard to find. 

Please be very careful, this is electricity. Theoretically thermostat wires are low voltage wires that don't carry a lot of Amps but you may have a short so you never know. 

Outside chance that the venter motor has a short or is failing. This is the little fan that first starts on a call for heat. 

Might also be internal to the furnace, on the safety circuit. These wires are surrounded by line voltage wires. 

I've never seen or felt the need for a power strip. There are resettable circuit breakers that are 3 amp at hvac supply houses. It  sorta would save you some money on fuses, Lil popper, but it costs 10-25  dollars. 

Was the on off switch the one on the gas valve? 

What did you jump to get the heat to work?

Have you changed the thermostat recently?

Did you hang any pictures lately?

Is the thermostat wire located in the attic where it can be stepped on?

This is dealing with electricity, I'll help as much as I can but if the budget can stand it a call to a hvac pro might be a good idea. A good one could isolate the thermostat control circuit, from the stat to the furnace in about five minutes.