A frame assembly adapted for installation in a filter housing, the frame assembly comprising: a frame adapted to receive a filter unit of a predetermined size, said frame having a front member, two side members and a back member, which form the frame and which together encompass an open aperture which is dimensioned to fit a filtering area of the filer unit, said open aperture adapted to allow air to pass therethrough; and at least one clamping mechanism for clamping said filter unit, said clamping mechanism comprising an actuator arranged at said front member, wherein said actuator is operable between an open position, wherein the clamping mechanism has not been actuated and the filter unit is not clamped, and a closed position, wherein the clamping mechanism has been actuated and the filter unit is clamped, while activating the clamping mechanism, wherein the clamping mechanism is arranged to clamp said filter unit by dislocating the frame from the filter housing, in a y-direction perpendicular to the frame assembly, thereby pressing the filter unit against an inner surface of said filter housing, wherein the inner surface is arranged to encompass an air intake area of the filter housing; characterized in that said actuator is arranged having at least one protruding portion facing said back member so that during operation of said actuator a free distance d between the protruding portion and the back member of the frame corresponds to an in-depth size of said predetermined filter unit size, thereby enabling operation of the actuator between said open and said closed position only if said inserted filter unit abuts said back member of the frame. a frame adapted to receive a filter unit of a predetermined size, said frame having a front member, two side members and a back member, which form the frame and which together encompass an open aperture which is dimensioned to fit a filtering area of the filer unit, said open aperture adapted to allow air to pass therethrough; and at least one clamping mechanism for clamping said filter unit, said clamping mechanism comprising an actuator arranged at said front member, wherein said actuator is operable between an open position, wherein the clamping mechanism has not been actuated and the filter unit is not clamped, and a closed position, wherein the clamping mechanism has been actuated and the filter unit is clamped, while activating the clamping mechanism, wherein the clamping mechanism is arranged to clamp said filter unit by dislocating the frame from the filter housing, in a y-direction perpendicular to the frame assembly, thereby pressing the filter unit against an inner surface of said filter housing, wherein the inner surface is arranged to encompass an air intake area of the filter housing; characterized in that said actuator is arranged having at least one protruding portion facing said back member so that during operation of said actuator a free distance d between the protruding portion and the back member of the frame corresponds to an in-depth size of said predetermined filter unit size, thereby enabling operation of the actuator between said open and said closed position only if said inserted filter unit abuts said back member of the frame.