Nest thermostat, on heat setting blows cold air

[Tstewartjr]

When the thermostat turns on the heat, the fan come on, but the air is not heated, it’s cold. Gas heat, forced air.

[laurentbourg]

Please upload a picture of your wiring

[luisoyola]

It is normal for my fan to blow a little cold air for about 40sec and then after start throwing the hot air?