Heating problems

My heating almost doesn't work on the highway in winter. I am changing the thermostats of my 1992 4.2 V8 because the temperature only goes over 80 degrees in the traffic jam. According to the climate display channel 8 shows constant "16,7", channel 10 varying values. Does this mean that the actuator motor is fixed or broken? And if so, where do you find him? In the console, or where? Are there any tricks in the installation or extension?

Geered VA