Furnace blows cold air

The blower runs but supply air is cool or cold.

Heating

normal

Diagnosed here

Gas Furnace: No Heat
Troubleshooting
The furnace is calling for heat but the burners never light, or they light and then shut down.

Background

Gas Furnace Sequence of Operation
Concept
Step by step through a call for heat on a modern induced draft furnace, and what each step proves.

Local Code Notice

HVAC installation, venting, combustion air, ventilation air, gas piping, clearances, termination locations, electrical requirements, permits, and equipment requirements vary by jurisdiction and equipment. Always verify the applicable local codes, adopted code edition, regulations, permits, and manufacturer installation instructions before installation or service.