My heater doesnt get or stay hot all the time or stay on the setting i put it on on 2000 Infiniti G20

The heater changes on its own all the time. I set it to hot then it never gets hot, it also chnages to a cooler temp or sometimes it gets hot then changes to cold or a higher setting or lower setting or it changes modes like floor or floor and vent or floor only or defrost? It does this all byI need heat with the wether here in Colordo? I checked the fuse box under the steering my fuses are fine. PLease help???

Asked by for the 2000 Infiniti G20
maybe the control unit is not working properly