Hello XXXXXX.
If you look under the hood you will find a relay box, the relay that you are going to be replacing will be the number 4 blower motor relay. We want to check this first before we start tearing everything apart.
You will ahve to replace this first and see if it fixes your problem. If not then you can back at a later time and post a new question and contact me so that I can continue helping you.
Auto Mechanic
Auto Business owner, 15 yrs experience, ASE certified