I'm no expert, just a shade tree hack
Anyway my climate control was acting up kind of like you have. I would have no fan at all in heat mode or if the control knob was turned to heat. Not even defrost unless it was in the blue zone. A/C would work as designed. My problem was a faulty push button unit. (PBU) There are several posts here on where to buy a rebuilt unit. What I did was pull my PBU and resolder all the connections. It brought it back to life. My uint has a rebuilt sticker on it and from the looks of the copper traces on the board the rebuild company just went over them with solder and reflowed all the pins. When this unit is in operation it get very HOT. I think over time the heat cracks the traces.