To eliminate and install a heater control valve on E30 models, you start by disconnecting the negative battery terminal and removing the center console as well as instrument panel trim. Drain coolant; detach hoses that are used to transport the coolant from the control valve; and remove wire connections. Loosen the clamp of the coolant pipe and get rid of bolts that hold it at heater connections and pipe. At the connectors, replace O-rings then reassemble valve/pipe as shown in Figure 10-20. Connect the firewall hose for coolant, reinstall console/trim, fill/bleed cooling system and reconnect negative battery cable. For E36 models, unplug electrical plug from heater control valve then drain coolant. Disconnect hose connections then pull rubber mount off valve assembly. Put upper part of valve into mount, pressing bottom part into mount when installing it(Numrich Auto Parts Corporation). Reconnect electrical plug to it at this time while putting back hoses at their original position. Fill up/bleed the cooling system (BMW AG). It is highly recommended to have these units serviced by skilled automotive technician who has been certified by relevant authorities (Davidovich). Open glove compartment door to remove microfilter which cleans air entering passenger compartment and take out inner trim (figure 10-21). Take off screws holding cover on side of heater unit then remove glove compartment door for replacement purposes only (BMW AG). After installing new filter you must not forget put back its cover hence enclosing glove box door too.