We have a coleman furnace 56000btu, the problem is green lights come on constuntly flashing. The control board has been changed, even changed the electronic thermostat, the MDU man said nothing was wrong, but it keeps shutting down. If you turn it off and then turn back on it works, but does the same thing.. keeps shutting down.

If it has a flame sensor clean it. See this link

https://www.askmehelpdesk.com/heating-air-conditioning/gibson-model-kg6ra-072c-12a-432525.html

Where is it located... and why does it work most of the time.

It is in the furnace burner area.

My husband had done what the diagram showed in #2 and used sandpaper, but nothing has changed, sorry for taking so long to answer back, but I had to go to work and husband doesn't know how to run my laptop.

Is this furnace located in a mobile home?

What is the exact model number?

In a mobile home. Model #
DGAT056BDD

On mobile home units here is the place to go. Sign in and post your model and question under Coleman. They are mobile home specialists and might even have the parts which can be hard to come by if you need one. You might also fine valuable info there for other items also.

Index page (http://www.mobilehomerepair.com/phpbb/index.php)