Abstract: An indoor climate control system in which a climate controlling equipment (1) has a control line (2) arranged to be connected to climate influenced impedance means (3), switching means (4) being arranged to disconnect the climate influenced impedance means from the control line under influence from a third output (5) of a control unit (6) and to instead connect substituting means (7) providing an impedance controlled by a first output (8) of the control unit, the control unit having polarity probing means (13) arranged to obtain an indication whether a connection of the substituting means to the control line results in a voltage with a positive or negative polarity, the connection of the substituting means being made in dependence on that indication and under influence of a second output (14) of the control unit.

Abstract: The invention relates to an electric system, comprising an electric equipment (1) having a control line (2) arranged to be connected to impedance means (3) as well as to substituting means (7). The substitution means provides an impedance controlled by a first output (8) of a control unit (6), the control unit having polarity probing means (13) arranged to obtain an indication whether a connection of the substituting means to the control line (2) results in a voltage with a positive or negative polarity. The connection of the substituting means (7) is made in dependence on that indication and under influence of a second output (14) of the control unit. According to the invention, the substituting means (7) comprise a series connection of two equivalent impedance networks (15, 16) provided each one with by-pass switching means (17, 18) for a plurality of impedance means (19, 20), each having series connected semiconductor switching means (21, 22) arranged in opposite directions.