why does my heater blows gold air rather then hot? on 1997 Mercedes-Benz E420

i turn on the heater and cold air blows out on the driver side but on the passenger side it blows a little warm. what might be the problem and where can i find it in the the car?

Asked by for the 1997 Mercedes-Benz E420
Most likely low of water or the heater core is stopped up or check the thermostat to see if it opens too fast.I would change the thermostat 1st.
okay thank you. do you know where is the heater core located