So I have a 95 525ia with 185000kms on it. It runs great. But yesterday as I was driving home I noticed that the heat on my side was nice and toasty and the heat on the passenger side was somewhat cold. No where near what my side was. Both the heater knobs were at hot (24). So my question is, what is causing this? Is it the heater control valve. Over the weekend, it was my side that was cold and the passenger side was hot. Is the HCV sticking perhaps? This is driving me . Any input would be appreciated.

Brian