My Trane BLU model blower cycles on and off about every 5 seconds when theromstat activates furnace to turn on heat up to the set temperature. While the burners are activated the blower turns on for about 5-10 seconds and then turns off for about 5 seconds then turns on for 5-10 seconds and so on, until it reaches the set temp. on the thermostat. Do you think this is the temp sensor in the furnace.

Thanks.

Could be the fan/limit switch in your furnace, Control board or a lose wire. Maybe even your fan moter is going bad. Do you have ac or a fan on switch on your t-stat if so try it to make sure nothing is wrong with the motor itself. What year is your furnace? And does it vent with metal or plastic pipe?

If your furnace is over five years old it could be your limit switch or a dirty evaporator coil if you have Central air conditioning with it.

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Originally Posted by Joshdta

Could be the fan/limit switch in your furnace, Control board or a lose wire. Maybe even your fan moter is going bad. Do you have ac or a fan on switch on your t-stat if so try it to make sure nothing is wrong with the motor itself. What year is your furnace? and does it vent with metal or plastic pipe?

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The blower does stay on if turn the Fan switch to On instead of Auto. My furnace was manufactured 12/85. It vents with a metal pipe.

Lets have a pic of the inside of your furnace and we will point you in the right direction.

Sounds like a faulty fan switch(or fan/limit switch) Just need to know what type of fan control you have so we can help you out. Im not real familiar with that year trane, so I would need some pics to see what they used.

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Originally Posted by mygirlsdad77

lets have a pic of the inside of your furnace and we will point you in the right direction.

sounds like a faulty fan switch(or fan/limit switch) Just need to know what type of fan control you have so we can help you out. Im not real familiar with that year trane, so i would need some pics to see what they used.

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Here are the requested picts. Let me know if you need to see more and I will take and upload again.

http://s600.photobucket.com/albums/tt83/nswien/

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Originally Posted by mygirlsdad77

lets have a pic of the inside of your furnace and we will point you in the right direction.

sounds like a faulty fan switch(or fan/limit switch) Just need to know what type of fan control you have so we can help you out. Im not real familiar with that year trane, so i would need some pics to see what they used.

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Try this link: Pictures by nswien - Photobucket

Great pics. There it is. The last pic shows the fan limit switch(located directly above the gas valve on the inside wall of the furnace. The one with the round dial on it. This is a honeywell fan/limit switch. There should be four wires connected to it(hard to tell from the pic) Watch the dial, when the flame comes on, it should turn clockwise until it hits the second peg on wheel.(alligning with the aroww at the bottom center of wheel) this is when the fan should turn on. Now once fan turns on, the wheel should either stay stationary, or move just a bit in the clockwise direction. If when the blower turns on, the circular wheel starts going back counterclockwise until it hits the first peg(which shuts blower off) then this control is worn out. Watch what happens and let me know. If this is the case(and I almost guarantee that it is, we will help you find the replacement part. Easy to change. Good luck and please let us know what you see.

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Originally Posted by mygirlsdad77

great pics. there it is. the last pic shows the fan limit switch(located directly above the gas valve on the inside wall of the furnace. the one with the round dial on it. This is a honeywell fan/limit switch. there should be four wires connected to it(hard to tell from the pic) Watch the dial, when the flame comes on, it should turn clockwise untill it hits the second peg on wheel.(alligning with the aroww at the bottom center of wheel) this is when the fan should turn on. Now once fan turns on, the wheel should either stay stationary, or move just a bit in the clockwise direction. If when the blower turns on, the circular wheel starts going back counterclockwise untill it hits the first peg(which shuts blower off) then this control is worn out. Watch what happens and let me know. If this is the case(and i almost gaurantee that it is, we will help you find the replacement part. Easy to change. Good luck and please let us know what you see.

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You got it ! That's exactly what is happening. Once the dial gets to the blower temp, it almost immediately turns counterclockwise and shuts off. Below is a link to picts of the info plate.

Model # is BLU080E942B1

Picasa Web Albums - Neal - Furnace Picts

Thanks, very helpful.

Sorry I can't read the print on the pics. But at this point I don't need the model and serial of furnace. This is a very common part(for older furnaces). Just make sure you write down which wires go to which spots on control. Then remove control. Take it to any heating company in town, and they will either have it on hand, or be able to order it for you. Now,, you will want to pay close attention to the jumper on the bottom middle of fan/limit control. This decides whether your limit control is 24v or 120v. All you will need to do is look closely at the new control and make sure it is the same as the old control. You will be able to ask the person you buy it from if the jumper needs to be broken off or not.. All of these controls come with the jumper in place. Please let me know if you need more help with this. Or go to honeywell fan/limit online and search for the control that looks like yours.

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Originally Posted by letmetellu

One thing to add to what mygirlsdad said is to watch the little dial as he burners are burning and if it continues to raise the temperature, instead of going up and down like he said, I think that would indicate a dirty filter or dirty coil, But I am sure you have checked the filter by now so I would say coil.

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At this point, the furnace is not going out on high limit. If it kept going clockwise until it hit the third peg, the burners would shut off, and the blower would keep running until the temp cooled enough to let burners come back on. This is not the problem the asker is having. The blower is turning on and off, which shows a fualty fan control,(same as if there were too much air flow, opposite of not enough air flow) I promise this is just a bad fan/limit. Replace it and all will be well.

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Originally Posted by mygirlsdad77

Sorry i can't read the print on the pics. But at this point i dont need the model and serial of furnace. This is a very common part(for older furnaces). Just make sure you write down which wires go to which spots on control. Then remove control. Take it to any heating company in town, and they will either have it on hand, or be able to order it for you. Now,,,, you will want to pay close attention to the jumper on the bottom middle of fan/limit control. This decides wether your limit control is 24v or 120v. All you will need to do is look closely at the new control and make sure it is the same as the old control. You will be able to ask the person you buy it from if the jumper needs to be broken off or not.. All of these controls come with the jumper in place. Please let me know if you need more help with this. or go to honeywell fan/limit online and search for the controll that looks like yours.

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Great. Thanks so much for your quick read on this issue and your helpful and clear instruction.

No problem. Please let me know how things work out, and if it indeed solves your problem, please give me a rating, if it doesn't help, just come on back and we will take the next step. Take care.

Lee

Hi,
I have the same unit but a different problem.
I noticed ice on the evaporator line and the next day the blower was not moving. It makes a loud humm but it isn't running. I took it ou and it has 24 years of dust in the motor. There is also a large cap on the side of the blower.

I'm assuming that the motor is shot and I am looking to replace it, right assumption? Or should I try something else first?
Thanks,
cbozzone

cbozzone, you will get more help if you start your own post. A lot of people won't see it here. Now, I would check the cap first, if cap is good, then yes, you will need a new motor. Even if cap is good, replace it when you replace motor.

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Originally Posted by mygirlsdad77

cbozzone, you will get more help if you start your own post. A lot of people wont see it here. Now, i would check the cap first, if cap is good, then yes, you will need a new motor. Even if cap is good, replace it when you replace motor.

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Oops. I'll do that next time.
I did end up needing a new motor which I got at Grainger for about $115. At the same time I had a quote from Shumate to replace the motor for $544. It pays to do it yourself. Thanks!

Glad you got er fixed, good job.