Heat will blow out hot air then go to cold air what would cause this

Sounds like a temperature blending issue inside the vehicle, driven by temperature controls. Do you have a controller that sets a specific temperature to be kept at? If so, the computer is adjusting the hot and cold as needed to suit the measured temperature inside the vehicle against what is set. If this is the case, there must be a malfunction. Another possible and less likely cause is that the engine temperature is suddenly dropping too low. Either way requires hands on testing to find out what is happening. www.repairpal.com/repair-shops