Furnace blowing cold.

Since this is an older unit, I would agree with checking the "sail" switch. The "sail" switch is a metal flapper on an arm. Basically, when you first start the furnace, the fan starts up to clear the unit of any gas. Once the fan gets moving, the air flow forces the "sail" switch to move. Once it moves, it turns on the gas and allows the unit to ignite. Sometimes, these switches get stuck. Often you can look inside and see the flapper and check to see if it's moving.

Don't circumvent the "sail" switch.