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Discussion Starter · #1 · (Edited)
Hi,

My furnace was coming on and then the burners were turning off after 5 minutes and the LED was blinking 4 times. I found the codes and wiring inside the panel and it says that it is the "high limit device". I changed the device in this picture and now here is what happens.

When I have my thermostat set below the current temp I have a nice consistent slow blinking light. When I turn it up above the current temp, the fan comes on, but now my burners do not come on at all and the LED is blinking 4 times. Any thoughts?

The furnace model# ADD100C945D0

Thanks, Rob
 

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a high limit is a safety device installed in your furnace to keep you from burning your house down. It is located in the air stream @ the heat exchanger. When the limit trips or "opens" it means that something is restricting the air flow. The most common culprit is a dirty filter and or a dirty evaporator coil.
 

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Discussion Starter · #3 ·
Changed the air filters

You were helping me on my other thread. Thank you.

The filters were the start of the problem and have been changed. I have no idea how to find the coil. If I took a picture of my furnace, could you help me?
 

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Discussion Starter · #4 · (Edited)
Furnace

Attached are the pictures of the full furnace with the covers on, the bottom section with the cover off and the top with section with the cover off.

Again any help letting me know where the coil is that I would need to clean is greatly appreciated!
 

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That looks like a downflow furnace, the evaporator coil (used for cooling) would be below the furnace if it is present.

Have you reset the power switch to the furnace after replacing the dirty air filter?
 

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there is one thing i want you to look at......you have a counter flow furnace.....in other words the blower is at the top and the burners are at the bottom,I have seen many many many MANY times were on Trane and American standard counter flow furnaces were the glue that holds the blower compartment insulation is sub par, it dries out and the insulation gets sucked up against the blower on both sides......causing limits to trip....there are limits or i should say, there is a limit in the blower compartment on your unit..I cant see into the blower area in the pictures that you have posted. If its not an issue then you will need to access the evaporator underneath the furnace and see if It is plugged. What part of the country do you live in if you don't mind me asking?
 

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there is a secondary limit mounted on top of or the back or side of the fan housing and it may have a red manual reset button which needs pressing.
 

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Discussion Starter · #8 · (Edited)
Probably about as far as I can go

@HarleyRider: I'm in Oregon and starting to wonder if I am as far as I can go. Under the furnace is sheet metal held together with screws, but things are coming out and sealed off. I'm probably going to have to call another professional. I'm avoiding it because the first one that came out changed a filter and charged me $120 and obviously didn't correct the problem.

As for a reset button, their isn't a visible one on the outside of the three sides I can see and I can't get to the back since it is flush against the wall.

Is there another picture that I could take and post that might give me a chance of not having to call someone?

Again, I appreciate all of the help.

Rob
 

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@HarleyRider: I'm in Oregon and starting to wonder if I am as far as I can go. Under the furnace is sheet metal held together with screws, but things are coming out and sealed off. I'm probably going to have to call another professional. I'm avoiding it because the first one that came out changed a filter and charged me $120 and obviously didn't correct the problem.

As for a reset button, their isn't a visible one on the outside of the three sides I can see and I can't get to the back since it is flush against the wall.

Is there another picture that I could take and post that might give me a chance of not having to call someone?

Again, I appreciate all of the help.

Rob

in the bottom picture is the blower area......turn off the power, remove the circut board and mounting bracket, then remove the flue pipe. You will be left looking at the cover to the blower compartment, remove that and then you will be looking at the blower. On either side of the blower is insulation that acts as sound deadening material. Is this firmly attached or is it "flapping in the breeze"? If it is lose remove it by removing the two screws from the out side of the cabinet, this will release the two 1" strips of metal that was keeping the insulation from getting sucked all the way into your blower. Now look for the limit(s) in the blower housing and ohm them out to see if they are open or closed.

Let me know what you find.
 

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Discussion Starter · #11 ·
Picture of what I have found

I removed the circut board and mounting bracket and then remove the flue pipe. The attached picture is what I am now looking down at.

I didn't find any insulation or the limit(s) in the blower housing. :(
 

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I more panel.......your almost there !
 

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yes the insulation looks good,the only way to check that limit is with a meter or a continuity tester, how about the insulation on the other side of the blower?
 

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Discussion Starter · #15 ·
Next step

The insulation on the other side looks the same. :)

I went and got a meter. When I put the meter on the new other limit part it comes up zero. When I put it on this part it comes up with a number larger than 0, but I don't know what to put the tester on. It has options for 200, 2k, 20k, 200k, 2m under OHM.
 

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You can TEMPORARILY AND I MEAN TEMPORARILY jumper it out to see if it is the problem. It may be partly/lightly/weakly closed. Should have 0 ohms resistance if closed.
 

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doesn't matter what scale its on.....just ohms is fine, then touch the leads together and observer what the reading is......now with the two yellow wires OFF the limit, touch 1 lead to each tab on the limit at the same time.....the results should be the same as when you touched the leads together, if not then the limit is tripped. remove the limit and smack it down on a hard flat surface and check it again. Also check you private messages.
 
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Discussion Starter · #18 ·
Eureka!

I love the fact that "smack it down on a hard flat surface and check it again." was the solution. Thanks for all of the help! Do I have to worry about the part that I slapped on the concrete?
 

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I love the fact that "smack it down on a hard flat surface and check it again." was the solution. Thanks for all of the help! Do I have to worry about the part that I slapped on the concrete?

Only if you dont keep your filter changed on a regular basis, BTW we call that "tricks of the trade"......glad its working.
 

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Just spent $123 to find out the 4 light flash was a $15 replacement part! It was the capacitor that sits on top of the blower housing. Just remove the filters and it's located on the top left side. Hopes this helps someone in the future!
 
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