It appears you have a manual control system.
The red/blue **** is supposed to open/close the heater control valve. This valve controls coolant moving through the heater core. Unless the **** is moved fully in the blue direction, the valve will be open to some degree.
The valve is located in the engine compartment, drivers side. You should see a couple of 1 inch diameter +/- hoses going into the firewall. One has the valve inserted into it, a control cable runs to the valve.
may have a photo of the valve.
Make sure that for some reason the A/C compressor is not constantly on. Start the engine, have someone press on the A/C button while you watch the compressor. When the switch is pushed the pump should start along with the coolant fans.
The pump uses a magnetic clutch to engage its drive pulley, thus the pulley is always turning. When the pump engages, the engine RPM should change a little in response to the increased load.