When I start my car to warm it and defrost the windows, it blows cold air even though the temperature gauge says it’s heated to the normal range, when I start driving-it blows warm air. Is this a the?

Did you read the forum replies above? We bought impala for our daughter and being Fall in Minnesota noticed she didn't have heat. Her air only warmed when she was driving and car moving, in park or idle there was no heat. I checked antifreeze and reservoir was bone dry. Filled that and she had heat again. Then two days later she called in a panic cause lights were off blinking on the dash and temp gauge was going up. I told her to turn off her heat and the gauge dropped down to middle. I met her and the overflow was almost dry so added more and noticed her fan was running even after the engine was turned off. It's never continued to run before (I assume it's running to cool) and stayed running for five min or so. I am not a mechanic, just a mom who researches and am driving to campus to try the remove radiator cap, rev engine and fill to remove any air bubbles as well as check the hose that is mentioned a few comments above your posted question and think I've got a good shot at fixing the problem and save money (hopefully) rather then buying thermostat and/or heater core first. This is definitely a faulty design AND FROM WHAT IVE READ IMPORTANT NO ONE OVERHEATS too badly or it can blow head gasket or piston (something expensive) causing you to spend ALOT MORE SO BE SURE TO RESOLVE PROBLEM before it causes more damage. Living in Minnesota it'll be cold and have no idea where the hose is but that's the lovely thing about technology and can look that up but after doing research for the past few days I feel confident I've figured it out and have a better then 50/50 chance of fixing the problem of air getting in the line and always us the pre-diluted or 50/50 universal blend living here in Minnesota where it gets butt cold!! My first "wanna be mechanic" fix here (I've never worked on a car but have always researched any mechanically issues wanting to make sure I wasn't getting ripped off or spend unnecessary money so I feel I know enough and definitely wouldn't feel confident without You Tube) and more so making this a lesson in independence to show my daughter how to research and problem solve and feel confident with possible easy fixes she can potentially handle herself in the future. If it doesn't work, at least we have elimated these two potential problems and will move to the next possible fix. Thankfully her college isn't too far and doesn't need to drive it til were sure it's been repaired so it doesn't cause worse damage. That's my biggest concern here at the moment. I apologize to the mechanics that are bored reading this but if our theory helps any other non mechanic then it was worth writing all this. I'll try to remember to come back and post whether or not we are successful.