My brother's furnace started blowing cold air one on of the coldest days of the winter. He called me over to help repair his system. This video shows step by step what the most common issues are and how you can correct them.

Primary Limit Switch - https://amzn.to/2YBShvH
always verify your part number by searching the make a model of your unit

Intro - 0:00
Cutting the Power - 0:15
Free Diagnostics and Cleaning - 2:00
LED Light Codes - 4:00
Testing Limit Switch 5:04
Replacing the Limit Switch 7:15

Here is a great list of error codes by brand with things to check.

http://www.grayfurnaceman.com/-ifc-fa...