Second, the cab cold and warm air conversion adjustment is not in place or the conversion adjustment motor is stuck. This is to check whether the replica of cold and warm air conversion is properly adjusted. If the adjustment is not in place, it will also lead to no warm air.
Third, the warm air caused by the blockage of the warm air tank is not hot. In this case, you can clear the warm air tank first, if not, you need to replace it with a new one! I hope my answer can help you.