Heater issues

During cold temperatures (outside) once car is started the heat will only blow from its current location. Example: controls set to dash and I set them to defrost, air continues to keep blowing from the dash. Heat will also not work, but air is blowing. After a few minutes I can turn the car off and then everything starts working correctly. Sometimes it takes driving it a few minutes then it will either start working or I will need to turn the car off and start it back up to get it to start working. Mechanics so far say that they can’t get it to replicate the issue, but I think they think that the heat is just not working and don’t understand. The heat works fine, just takes a few minutes for it to work and for the controls to start working. Any suggestions?