After some troubleshooting I have found that when the ignition control module sends a signal for the gas valve to open it does not open. Customer needs a new gas bales for system to run. Unit is a 32 year old 85,000btu Bard furnace that is way oversized for the ductwork that it is on. I advised to customer that with the age of the unit that is should be updated and the ductwork needs to be upsized