Can having air in the coolant system cause the heater not to blow hot air?
Absolutely. And it’ll also cause inaccurate temp sensor readings leading to operating problems, uneven engine temps possibly leading to a warped head, and a host of other problems.
Why do you ask?
Agree but the question is why is there air in the system?
It can be only one of two things.
Either the cooling system was serviced recently, and not properly purged of air.
Or, there’s a leak in the cooling system.
Or gulp, a head gasket.
changed the thermostat. got hot air…lol
Congratulations. Sometimes it’s the simple stuff.