I have a york diamond 90 gas furnace. When it is done heating it goes into the cool off mode it will not stop blowing cool air. Even when the furnace is off it stays running. Pulled off panel so the safety switch will shut it off as soon as I put door on it starts blowing again cool air. All the time the thermo is off

If the furnace is heating normally and the only thing that is having a problem is the furnace blower staying on all the time then the furnace fan and limit control or the fan blower relay is defective. Fan and limit controls look like the pics below for the most part. If you have a blower relay problem it is probably on the control board.

Look to make sure the tstat isn`t set on fan or fan only instead of auto,, if its on fan it will run all the time

Thank you guys for the help. Lets just say I feel like a complete dumb a?? The thermo was set to fan on instead of auto. I looked at it a hundred times before I even seen it set to on. Just blew it off thinking it was right. Well at least the furnace is clean. Thanks a lot guys. Just found this site I will be back. JEFF

LOL That has happened before but I usually do not post that since some people take offense when I tell them to check the blower setting on the thermostat. I had one poster call me a name I will not repete when he said I was very stupid to ask that since he was not that dumb.

I am glad it was a simple repair for you.

I`ve been called those names not worth repeted before it doesn`t bother me,, they are the ones who has to answer for it,, I just try to help if I can

You always need to get the easy problems out of the way first. THANKS GUYS