Fan/Blower 'ON' all the time

[ranchero]

I tried to change my old dial thermostat to a new Honeywell digital thermostat. My system has 5 wires. Red, Yellow, White, Green and Black. I understand the red, yellow, white, and green (it is labelled in the Honeywell schematic). But the Black one is not; the black wire is hooked to the old dial thermostat labelled TC. I corrected this black wire to the new Honeywell digital thermostat and when I turn the system back on (circuit breaker switch to 'ON'); the fan ran continuously with fan switch in the ON and Auto positions. I reinstalled the old dial thermostat but the fan still runs at both ON and Auto.

Did I fry some relays or the circuit board in the furnance?
Any suggestion will be apprepiated.

[Hube]

You have given very little info in order to advise properly...Was this black wire hooked upon the old one? In other words, did the old one require a 5 wire hook-up? When you hooked up the new one, what terminal did you hook this black wire to.? What type therm do you have now?What make/model was the old one? Is your heating unit Forced air gas/oil with air only? (no heat pump) Post back with info and we will advise further, Hube

[frank]

fan willnot shut off