Gas and Oil Home Heating Furnaces - Another blower always on question?

I have a carrier natural gas furnace (1978) that is controlled by an honeywell T stat. (1978) All has been fine until I switched it to heat and the heat cycle performs as normal but the blower remains on until I go to the T stat and lower the temp setting at least 10 degrees then the blower stops. I popped the cover off the T stat and notice two mercury vials. Looks like one turns on and off the gas furnace and one turns on and off the fan. The mercury doesn't move together as I figure they should or am I wrong? If I manually hold the vials down after the furnace (gas shuts off the blower will run the typical amount of time and then shut off as normal. Is this a thermostat problem or a furnace control problem. All the other posts I have seen they always have to shut the blower off by main power and i can do it at the T stat but have to manipulate the merc switches to get it done. Any help is appreciated. Thanks

Dont know what tstat you have there. But on heat the fan dont work from the tstat. On AC yes. Now take and jump R to W burner should come on and run then fan should come on.After fan is on for a while pull jumper burner should go off short time latter fan should stop. If not can be in the tstat. Will it go on and off with the fan switch on to auto.
That would work on the AC side .There the tstat turns the fan on with the AC.

ED ;)

Thanks for your reply. Let me answer your T stat question first. I have a mechanical Honeywell..Not sure of the model number but it has the heat pump as well. I don't use the heat pump feature as it is wired for the natural gas as the primary heat and has been working fine for a few years. I always leave the switch in auto and the furnace fires up then the blower comes on and never turns off, but if I move the temp adjust to a little lower setting the blower will turn off. I jumpered R+W and it did exactly as you said and the blower turned off as normal. Now I am confused as to what it could be if not the t stat. I thought that jumping R+W was a T stat bypass. I appreciate your help.
Thanks.

sounds very much like the stat. remove it completely and jump R and W for heat, R and G for fan. dual fuel is wired differently, if the heat pump is not used i would rewire it all for your needs

If I'm not mistaken, those furnaces had a little resister on a limit switch. Remove the cover and about mid way down, you'll see a limit switch on the wall of the heat exchanger compartment.

If that resister went bad, it would cause the blower to run continuously. The resister will need to be replaced.

Thanks all who replied. I was on travel and got home yesterday. I went to the local hardware store and bought a ritetemp t stat model 8085C. Installed and programmed it and all is working again. Besides the fact that it works it also looks cool if that matters. I appreciate your help. Thanks