Air conditioner only blows cold air from driver's side vent the rest are blowing warm air

I have four air vents, one on the driver's side door two in the middle, and one on the passenger side. When I turn on my air my side (the driver's side) vent blows out cold air, and the other three blow out warm air. Sometimes I can get it to work like normal. I took it to a shop to get it fix, and I was told that it was my air recirculating actuation door, and the part was $90.00, great! But all in all total cost is $848.00, I (lol) it is sad. I am going to try to do it myself. Is it one door I am looking for under my dashboard (glove box)? Thank you for your time and helping me. Sherri :)