Jorn is right - there is no resistor in his '92. But there is one in your '90; the complete heating/cooling system was redesigned in 1991, easily traced by the inline expansion valve and modern aluminum dryer located by the firewall in the newer AC systems.

You´re system won´t look like his, your fan should be the old type with only two connections and there will be a resistor inside the heater, nearby the fan motor. It´s famous for breaking and yes, you should have changed it while you were in there :-) As with the fan, you´ve got to get in there from the driver´s side.

The resistor won´t affect the passenger heat, however. Normally, there shouldn´t be a difference but if any of those tiny vacuum hoses came loose or were bent you might have a flap/valve which doesn´t open/close in the system. Loosen the panels, start the engine and try all the button combinations. Check the flaps of the left and right side correspondingly.

You could also loosen the speaker grille on top of the dashboard and check for previous owners(?) mistakes. Through the windhield you can see the heater hose connections this way. Since this internally is a 'Y' construction there is one outlet and two inlets (or was it the opposite? Don´t remember...), connected together on top of the heater. Check that noone has done something really stupid, such as clamped, bent or squeezed one of the tre inlet lines to the heater. You could also feel the heat of the left and right connections which of course should be equal.

/Martin