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Douglas, HVAC Technician
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I have a coleman dgaa070bdtb gas furnace. The green light

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I have a coleman dgaa070bdtb gas furnace. The green light is blinking four times. The cover says this means limit switch open. How do I fix this. Thank you
Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.

This could be several things but as it says the limit switch is open.

The limit can be multiple limits in a series, and if any one of them trips, the circuit is opened.

If you remove the cover of the furnace where the burners are (not the blower section) you may see several small disk shaped controls, about the size of a quarter mounted above, below or to the side of the burners. They will each have two wires leading to them and will have a button, about the size of a pencil erasor (or smaller) in the center between where the wires connect. Here is a picture of a similar control...


With the power off, press the button on each of these and see if one clicks as if resetting.

There may be several but usually mounted right by the burner outlets where the flame would normally be

Customer: replied 3 years ago.

how do i remove the cover where the burners are not sure im looking in right spot

I really mean the main door, not so much the burner cover itself. These little discs should be mounted on the burner box.
Customer: replied 3 years ago.

I only have one burner like a torch. i have the assembly out. it looks like an exnighter and a torch head i dont see any disk shaped controls my furnace is only a couple of years old if that makes a difference may be 2 or 3 tears old

Ok is it still flashing the fault?

Do you see a limit mounted on the fire wall? Its usually about 1.5" wide and 2" tall that has two wires leading to it. the limit itself may look to me made of carbon fiber or something
Customer: replied 3 years ago.

i have above the burner somr thing that looks like what you talked about first it unscrewed right out of the wall of the furnace the side that was inside looks 3/4 inch or so and i can pop it in and out the side outside has two wires but no button

thats a thermal disk...

Take the two wires off that and hold them together firmly. You can use a pair of pliers or a closthispin or something, If you dont have either of those straighten out a metal paperclip and stick it in one and then the other. Power the furnace back up and see if it still trips.
Customer: replied 3 years ago.

i did what you said but like an idiot i let the paper clip touch the furnace and blew my 3 amp fuse i need to run out and get one. at the same time it took a minute before this happened and the fan was just running same lights etc.four flashes

Ok... well let me know when you get the fuse... prior to it blowing, you still had the 4 flashes?
Customer: replied 3 years ago.

yes still four flashes be back in 1/2 hour

get some spares... LOL
Customer: replied 3 years ago.

back with fuses. i put fuse in and papercliped wires together turned on. furnace fan ran for a few min then stopped. green light still flashing four

Ok.. you can put that limit back in and rewire it. We need to find the main limit. If you follow those wires, you may get to it, they are likely wired in series
Customer: replied 3 years ago.

i found a limit which needed to be reset. when i turned the furnace back on it cycled and then started flashing once ignition failure the furnace ran without tripping the limit but now is tripping a flame fault?

DId the burner come on?

Customer: replied 3 years ago.

no it wants to but just wont fire

does the ignitor work?
Customer: replied 3 years ago.

no does not seem to i here relays going on and of but see nothing through view hole

is this a hot surface ignitor? and no fault but the flame fault?
Customer: replied 3 years ago.

i think so when i had it a part in front of the main torch was some thing that looked like it would just heat up not a pilot light could i have bent it a little taking it in and out

Oh for sure, but not bent, its very fragile and you can pull it out and look again, it may have a hairline fracture in it. Simple to replace and common that they break, even just by looking at them funny.
Customer: replied 3 years ago.

are there other things i sould check before buying psrts pulling off cover now . Oh yeah i broke it. are there any other things i should lookat before getting part. and would any plumbing supply have or maybe home depot


You know just about any HVAC supply house has them, they all do.. Plumbing, maybe and Home Depot is hit and miss. It seems to depend on the store. I know I cant get them here at my local stores but I know of cases where they do.

I doubt a small hardware store would have them.

Look up Air Conditioning Wholesale or distributors in the yellow pages, they are usually tucked back off the main roads.

Really I think its all good, just replace that and be careful with it. Never touch the black part (oils on your fingers). Get a spare to keep because its always the coldest day of the year in the middle of the night when they break, especially for those of us who live on what seems to be old Indian Burrial grounds. :) You cant do much else till you do this although you could use a bbq lighter to light the main burners durning the ignition sequence to get it past the ignitor phase to see how the rest works.
Customer: replied 3 years ago.

how do i get a hold of you later

you can just come back to this page... bookmark it.
Customer: replied 3 years ago.

thank you douglas i have a heater that seams to work what do i do next so you get $$$

Is it all working now?...?By the way, for my own benefit. Where did you get the ignitor?
If we are are all good, that makes me feel better.

If you are pleased with my help, and don't mind, please click accept and select a positive rating for me as this is how I am rewarded by the site. If you need anything, let me know.

Douglas and 2 other HVAC Specialists are ready to help you
I just wanted to make sure all is good with the furnace. If you haven't already, and you are pleased with my assistance, please consider accepting my answer and offering a positive rating.

Thanks again,

Customer: replied 3 years ago.

douglass thank you for your help i gave you the best rating possible. you were very helpful. i am truly sorry i could noy give you a tip. thanks again keith

I am happy that you are now warm and pleased. Glad to hear it and thanks!

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