The heater on the earlier 107 cars was turned on and off by a valve mounted on the firewall opening and closing. As soon as you move one of the red heater levers up slightly, the valve opens fully. You control the amount of air passing over the core with those levers. Each lever controls a flap in the heater box. Over time the hinge on the flaps go kaputin and you can't control the heat.The whole dash and heater box have to come out. I've never found a way to repair one.
Auto Zentral Ltd.