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realali · Sep 13, 2012, 12:34 PM

My renter tried to change the stat, now the fan is running all the time.
The Manual says check Fuse line, but I can not locate it !
http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/ii394g-25-1.pdf

I have changed the switch limit so far, and removed the thermostat, still the fan is running.

Need to knowwhere is the fuse line/

Grady White · Sep 14, 2012, 05:34 PM

If the furnace has a circuit board, there is often a fuse on it. These fuses are of the automotive blade style & usually either 3 or 5 amp.

EDIT: In the troubleshooting section of the manual to which you linked it states one cause of the fan staying on is a blown fusible link. They must be replaced with an identical part. Find the 120 to 24 volt transformer & follow the output from the 24 volt side. The fusible link shouldn't be far from the transformer output.

realali · Sep 16, 2012, 08:50 AM

I changed the fuse link
And then replaced the old borad with a brand new one the board
, the new borad has a fuse (3 amp )on it.
As soon as I truned it on, the new 3 amp sparked and burned.
I assume if I change the 3 amp it should not last eathier...

What should I do next?

Grady White · Sep 16, 2012, 09:00 AM

Originally Posted by realali

I changed the fuse link
and then replaced the old borad with a brand new one the board
, the new borad has a fuse (3 amp )on it.
as soon as I truned it on, the new 3 amp sparked and burned.
I assume if I chnage the 3 amp it should not last eathier...

what should I do next?

You have a short somewhere. Disconnect the thermostat wires at the furnace, replace the fuse & try again. If the fuse doesn't blow, the problem is in the stat or wiring.

realali · Sep 16, 2012, 09:07 AM

Originally Posted by Grady White

You have a short somewhere. Disconnect the thermostat wires at the furnace, replace the fuse & try again. If the fuse doesn't blow, the problem is in the stat or wiring.

When the fuse blew the last time, I had the stat wiring discounnected. Only two balck wires were connected.

So I am sure the stat is not shorted.

Grady White · Sep 16, 2012, 09:11 AM

Originally Posted by realali

When the fuse blew the last time, I had the stat wiring discounnected. Only two balck wires were connected.

So I am sure the stat is not shorted.

Were the wires disconnected at the stat or at the furnace? If only at the stat, the wires could be shorted due to a mouse chewing on the insulation, etc.
Where do these two black wires come from & go to?

realali · Sep 16, 2012, 09:23 AM

Originally Posted by Grady White

Were the wires disconnected at the stat or at the furnace? If only at the stat, the wires could be shorted due to a mouse chewing on the insulation, etc.
Where do these two black wires come from & go to?

Discounnected in the furnace, so the wirring to the stat was nothing do with blown fuse.

The two black wire are connected to C and Y

I asummed they are the power to the unit.
If not, then are they coming from,A/C ?

Grady White · Sep 16, 2012, 09:43 AM

Originally Posted by realali

The two black wire are connected to C and Y.
If not, then are they comming from,A/C ?

They do go to the A/C outdoor unit. I'd disconnect them too, just to eliminate any possibilities external to the furnace.

realali · Sep 16, 2012, 09:52 AM

Originally Posted by Grady White

They do go to the A/C outdoor unit. I'd disconnect them too, just to eliminate any possibilities external to the furnace.

Thanks for you help
I will try that this aftroon and post results tonight.

realali · Sep 16, 2012, 07:23 PM

Frist-I got the two wire (A/Cs) diconnected and had only the t. stat wires connected.
And put new 3 AMP fuse.
The fan stopped running. I thought it was fixed.
So I wend to T. stat and put the fan "ON"
But to my surprise, the fan did not run.
I took the fuse out and the fan started running ( so when the board in it not running)-
Then I put fuse back and A/C wires connected. The fuse did not blow but the fan was not running eaither.
Out side temp was around 70F so I put the stat to 80F to see if the furnace ignited.
Nothing! No ignition for 4 minutes, I gave up for the night.
I am now confused.

Grady White · Sep 17, 2012, 06:28 PM

If you have a digital t-stat, depending upon make, you could have up to a 5 minute delay after powering up. You very well be frustrated by that delay. When they say 5 minutes, they mean at least 5 minutes but never less.

The fan runs with the fuse out just as if the fuse were blown. I guess it's supposed to be some sort of safety thing??

realali · Sep 18, 2012, 02:05 PM

Here is current status, since It is getting cold around here I appreciate any help I can get:I checked the tranformer In 120 out 27.7 V
I put new fuse, No fan, so I shorted G (Fan) to R and got the fan running
Then I shorted W (heat) to R and got he sparks.
So I removed the new T. stat and put theold one back. Put the fan on "ON" fan started. Put the stat on Auto the fan stopped that is good.
I believe the Fan is fixed with the change of control board, limit switch & Fuse link
But the put the t. stat on heat 90F the furance started to sparked for several minutes but did not ignite. After several minutes I put the heat on "OFF" so not damge something else.

Now I might have new problem which is
" the heat does not strat ( gas is not ignite depite sparks)Did I damge something else? What should I do next.to get the heat

realali · Sep 18, 2012, 02:09 PM

Originally Posted by realali

Here is current status, since It is getting cold around here I appreciate any help I can get:I checked the tranformer In 120 out 27.7 V
I put new fuse, No fan, so I shorted G (Fan) to R and got the fan running
Then I shorted W (heat) to R and got he sparks.
so I removed the new T. stat and put theold one back. put the fan on "ON" fan started. Put the stat on Auto the fan stoped that is good.
I believe the Fan is fixed with the change of control board, limit switch & Fuse link
But the put the t. stat on heat 90F the furance started to sparked for several minutes but did not ignite. after several minutes I put the heat on "OFF" so not damge somthing else.

Now I might have new problem which is :
" the heat does not strat ( gas is not ignite depite sparks)Did I damge something else? what should I do next.to get the heat

Thanks

Grady White · Sep 18, 2012, 05:09 PM

It would seem you are not getting gas for one reason or another. First & simplest things to check are: (1) Make sure any manual gas shut off valves are open. (If propane ensure there is gas in the tank & the tank valve is on.)
(2) Check the gas valve on the furnace to verify it is set to "on".

Is there a small (1/4") aluminum tube attached to the gas valve? The presents or absence of said tube will tell me if the furnace uses a pilot (lit by the spark) or not.

realali · Sep 18, 2012, 05:36 PM

The valve is set to "ON"
It is natural gas not propane
The manual (link above) says do not try to lit the pilot manually & I can hear the sparks when heat is called for but no ignition ( at least for several minute that I was watching it)

Grady White · Sep 18, 2012, 07:01 PM

Originally Posted by realali

The valve is set to "ON"
It is natural gas not propane
The manual (link above) says do not try to lit the pilot manually & I can hear the sparks when heat is called for but no ignition ( at least for several minute that I was watching it)

Presuming the gas is turned on to the house, you have either a clogged pilot orifice or the furnace's gas valve is not allowing gas through.
Most gas valves have three terminals which are marked PV (pilot valve), MV (main valve) & a third marked Com, Comm, Common, or MV/PV. During the ignition sequence, measure the voltage between PV & Common. You should get +/- 24 volts AC. If you do, & hear a slight click the valve is getting power but is not opening or the pilot is clogged. Pilots can be easy or a bear to get out.