For the last couple weeks, my 1990 Nissan 300ZX didn’t have heat. The 300ZX uses a digital temperature control and seem like it still working when I increase/decrease the temperature: the air blow to defrost the windshield when temperature is hot, to the floor when it reduce to 75-80, and to the face when it reduce below 70. A/C is working fine, and the blower is working OK too. Temperature from the gauge is in the middle, and the antifreeze level is right. I’m thinking the problem is from the Temperature Control Valse but I’m not sure and I couldn’t find where it locate at. So if you can give me some advice about what’s wrong with my car temperature. Thank you very much.