Anyone know how to install a thermostat for an old furnace?

The furnace has 5 wires that goes to the old thermostat and one of the wires is black and labelled 4 on the old thermostat and i cant figure out what to do with it. I installed the new thermostat and i can get the fan to work but not the heat or the fan on auto.Anyone know how to install a thermostat for an old furnace?In general, if your thermostat was wired within normal standards originally, here is your color pattern:



R is usually red and is usually the hot side of the transformer.

C is usually black and is usually the common side of the transformer.

Y is usually yellow and is usually the cooling control (it turns on the outdoor unit).

G is usually green and is usually the fan control.

W is usually white and is usually heat.



I kept typing %26quot;usually%26quot; because there is a lot of variance in original installs depending on the installer and the make and model of the air handler and outdoor unit. It's a shame that you didn't label the wires before you took them off the old t-stat. Oh well, no matter. Check for 24VAC control voltage across the red wire and the black wire. Check for that first and then everything else should fall into place.Anyone know how to install a thermostat for an old furnace?you probably need a dual thermostat! it has two sencors one for each!