Hi
i have a trane xb80 furnace that was blowing cold air and as i read in this forum and according to the led code with flashing 4 times i found that i should change my swith limit , so i took out the switch it was l190f30 but the shop gave me l180f40 and told me it should work . I installed it on the furnace but it was blowing again colx air and whenever i was trying to put the temp above 23 it was stoping blowing air . And after a while it completely stop working . Now it's not working at alland it seams ghat there is no power in the furnace and the light is completely off . Please help we what to do ?

 

Make sure the blower door is fitted to the furnace properly. If OK, check the 3 amp automotive type fuse on the circuit board.

 

Hi
the problem is i can't find the fuse

 

There's a picture of it on the fifth post of the other XB80 thread.

 

The fuse should be located as shown in the attached photo circled in red.

 

Mine doesn't have fuse in this location

 

look at my board , i don't have it

 

Indeed you don't, at least not on that board. Do you have a voltmeter to measure ac volts?

 

The fuse that is supposed to be there is missing. The spot for it is there as shown by the red circle.

 

I will buy it tomorrow , what should i do ? Which wires on the pic , thanks a lot for your help

 

What is the part number on that board?
Geo

 

F1


It's written beside the supposed fuse location
did the switch limit cause the problem ?

 

Can it be measured by multimeter ? Is it same as voltmeter ?

 

Did you remove the 5 amp fuse? The furnace will not operate without the 5 amp fuse in place. The fuse protects the transformer and low voltage controls.

 

There is nothing there , no fuse at that location as it shown in the photo

 

I can't tell from the photo. Are there actually sockets for the fuse where firedawgsatx circled in red?

 

That's the reason you don't have the light indicating power on your control board. Somebody removed it since the last time your furnace operated properly or you would not have had 24V at the thermostat to send back to the furnace control board to operate it. Hopefully, your transformer is not damaged. You will need a meter to test the voltage coming out of the transformer.

Can you provide the model number of the control board. It will be shown on the cover of the board as shown in post #5. The photo I attached in that post is the original part number for the XB80 furnace.

 

If I'm not wrong D341828P01

 

No there is no sockets in that place.

 

I have the light led on the board but it's off

 

There is a sticker on the control board that shows D341122P01. You don't have a plastic cover that goes on the control board with the White-Rodgers model number?

You are saying that a 5A fuse, as shown, won't plug into that spot? From the photo you posted, it sure looks like a socket to me but the photo is a little fuzzy. Some boards just have a wire across that spot. If possible, please post a close-up clear photo of that spot.

 

attached is the photo from the board diagram
there is no cover on the board

 

a closer photo from the location of fuse

 

Ok, it appears to be one of the boards with just a wire instead of a fuse. You will need to test the voltage coming out of the transformer. Did you try to re-set the circuit breaker for the furnace to see if you can restore power?

 

How should i do that ? I dont know how to do that
if you mean reset it via electical panel , yes i did itthe number that i gave you before was the serial number
E
50A55-571
156-4341 rev.B
can it be the model number

 

Yes, the model number is 50A55-571. That is one of the boards that did not have a fuse installed on the board. When the board does not have a fuse a competent installer will wire in an in-line fuse to protect the transformer and low voltage wiring. If you follow the wires coming from the low voltage side of the transformer do you see what looks like a fuse holder? When I say you need to re-set the circuit breaker it will be inside the main electrical panel that provides power to the rest of your house. There should be a circuit breaker that is marked furnace. You will need to find that and turn it off and then back on to reset the furnace control board.

 

First of all thanks for your help and follow up , i appreciate that .
for the transformer there are just regular wires without anything like a fuse on them .

 

Ok, no fuse. Were you able to re-set the circuit breaker? I failed to ask, but are you pushing in the furnace safety door switch when checking for power to the control board?

 

Yes i did butnothing happened after reset .
For the switch door , yes i do
I'm frustrated now , i wanted to save some money , but i think i made a bigger trouble .

 

If re-setting the breaker didn't reset the control board that's about all you can do until you can use a meter to test voltages. You will need to set the meter to volts AC and with the door switch pushed in test to see if you have 120V going in and 24V coming out of the transformer. If you have 120V going in but no voltage coming out your transformer is bad and will need to be replaced.

 

Thanks man ! I will let you know tomorrow after i got the multimetet

 

I know it sounds really basic but sometimes we can't see the forrest for the trees:
Are you sure the emergency switch (usually ouside the furnace closet or at the top of the basement stairs) is on? How about another switch on or very near the furnace? Certainly can't hurt to double check.

 

Hi , i Checked the transformer when the switch is on , the voltage coming in is 123 but there is no voltage coming out .
does it mean that the transformer should be changed ? Can it be fixed ?if not did the high limit switch cause the problem ? How can i test the transfomer seprately to besure that the transformer is completely down ?
Thanks again

 

That would indicate the transformer is no good and will need to be replaced. To test the transformer separately you remove the wires coming from the low voltage side of the transformer and test across the two wires or terminals.

What caused the problem more than likely is because you do not have a fuse installed to protect the transformer. If you install a new transformer I highly suggest you install an in-line fuse holder with a 5 amp fuse on the low voltage side of the transformer. Radio Shack sells the fuse holder as well as auto supply stores.

You stated you changed the limit switch. How did you determine it was the limit switch that caused the issue and threw a 4-flash code? Did you use a meter to verify if the switch was open or was it a guess. According to the wiring diagram you posted there are four thermal protection devices in your furnace: one limit, two non-reset (fusible link) rollout switches and a reverse flow switch. Now that you have a meter you can check for continuity to see if any of the switches is open.

The attached photos should be similar to the roll-out switches you have in your furnace. I also attached a wiring diagram that shows the thermal protection circuit with a yellow line designating the path.

 

Thanks i checked ythem all and the switch limit was open , and for the fusible links and the other switch after about the test for the switches , it starts with 00.3 and after a few seconds it changed to 000 , is it OK
cheers

 

That is the limit switch you recently replaced?

You are looking for a reading of 0 or very close to it if the switch is closed. Did you verify the meter is working properly by touching the leads together to see if you get a reading of 0?

 

Both have this problem now they are not 0
ichecked it now by touching the two leads and the number is almost 0 , it's 00.3 when i put the ohm on 200

 

Unusual that a new limit switch would fail so quickly. If you replace it, I would replace it with the correct oem part number that has the proper temperature rating. There is not much else you can do at this point without power to the control board.

 

i checked again the limit switches . The result was exactly when i touched the two leads 00.3 so does it mean that the all of the other switches . All of the switches are fine . So what ? Does the transformer was the only problem ? So how the furnace was just blowing cold air the error code was 4 ?
the reason of making the furnace to hot may be the filter as it had not been changed for a while and it was too dirty . But the problem of having cold air was for a while something around 2-3 weeks . Are you still saying that it was just for the filter and there were no more problem . What was the problem of stop to blow air after i had set the temp over 23 deg . And why after i had reset the furnace before and after changing the switch the switched hasn't been reset . I should add that after i changed the limit switch, the error code was call to heat and i didn't have flame .

 

If you have an a/c evaporator coil installed it could also be clogged because the air filter was dirty. If the limit switches test good then the furnace may operate properly after the transformer is replaced. Until that time you can only guess.