coleman 90 series will not ignite

[danfab]

This seems to happen every time I go from AC to heat:
It seems to be an original coleman 90 series forced air system and the home is about 20 years old. I go to the basement, turn a few items from cool to heat then switch the thurmostat from off to heat. I hear the system turn on and I also hear the electronic pilot try to ignite...but it is not turning over and producing hot air (for lack of proper terms).
This took a few days to eventually correct itself last year. One evening, I just turned it on and finally heard it ignite and start to blow hot air.
Any idea what I am doing wrong? Or where I should start trouble shooting?
Getting a technician to the house will take over a week and it's getting cold out.
Any directions/assistance would be greatly appreciated.

[m kilgore]

Have you had your system serviced lately? After it took so long last year you should have had someone out to service the furnace. Do not mess with it yourself as you could hurt the family. Call for service now. If it takes a week you should have had it serviced sooner!