My 8 year old Trane XE80 heat comes on then when it cycles off the fan keeps running and I get 4 flash error code. Help please. Thanks

After replacing the limiter this problem still existed. After the frustration of trying to fix this problem i realized that the coils are all the way on the bottom of the unit pulling the cover off is a rodeo you can't take it off completely so I just bent the cover down looked inside and it was packed full of dust. Needless to say the air pushing down from the the top could not flow through the coils causing heat build up witch trips the limiter sensor. The cheapest and best way to fix this problem is to get a bottle of ac flow from Home Depot for 9.99 follow the directions (but it is best to use the garden hose method). After that I would suggest running the air conditioner set to a real low temp for an hour or two to let the natural water run down the coils to help with the cleaning process. Turn on the heat and this should solve you're problem. Hope this helps out.