Abstract: A method is described in which the operative condition of the cooling sections of a slot die for making flat films of thermoplastic material, or of an annular die of a blow molding extruder for making tubular films from synthetic thermoplastics, is tested. The cooling sections are provided with lines for supplying and discharging cooling air and the lines for supplying cooling air are connected, as required, to a central cooling air feed line, which is under superatmospheric pressure, by solenoid valves controlled by an electronic computer. In one embodiment of the invention, a testing program is performed in which the cooling air feed line is disconnected by a shut-off valve from the branch lines leading to respective solenoid valves when the latter are closed.

Abstract: Load resistors connected in parallel in a heating circuit having switches operable to connect and disconnect the resistors from a common supply line for heating a plurality of zones to maintain predetermined temperatures therein, are tested by disconnecting all of the load resistors from the supply line to begin a testing operation. Any current conducted when all load resistors are disconnected from the supply line is measured, after which the load resistors are then individually and successively reconnected to the supply line. The current then conducted from the supply line in succession to the load resistors is measured and compared with reference values of current through the load resistors when functioning properly.