Process for controlling a dryer suitable for dehumidifying air entering oil expansion vessels used in power electrical appliances, wherein said dryer comprises at least one outer protective casing, provided with locking flanges, where openings for outgoing dehumidified air are provided, and at least one sump for collecting, conveying and discharging outside condensate, wherein said protective casing surrounds two dehumidifying tanks or vessels (S1, S2), each of which has a plurality of micro-openings for entering the air to be dehumidified and one or more openings for outgoing the dehumidified air, each of said two dehumidifying tanks (S1, S2) also containing absorption means suitable to absorb the humidity of air coming from outside and said absorption means being thermally regenerated by means of resistors (R1, R2), each of which placed inside a dehumidifying tank (S1, S2) and connected with a ventilation means (V1, V2) of said tank (S1, S2), wherein at least one load cell is fixed to a first dehumidifying tank and is configured to determine the saturation state of said absorption means contained into said first dehumidifying tank through the conversion of an applied force into an electrical resistance variation, so that a detection by said load cell of a measured mass value of said absorption means greater than a predefined threshold value (Mfs, MS1) operates said resistors (R1, R2) in order to regenerate said absorption means to the original state, characterized in that said process comprises at least the following steps: - starting and setting at zero data relating to said load cell; - monitoring temperature values detected by a first temperature sensor placed inside said first dehumidifying tank, by a second temperature sensor placed inside a second dehumidifying tank and by a third temperature sensor placed inside said load cell and monitoring said mass value detected by said load cell; - comparing said mass value measured by said load cell with said predefined threshold value (Mfs); - sending an alarm signal, in case said measured mass value is greater than said predefined threshold value (Mfs); - data processing for computing a first mass value and for comparing said first mass value with at least one prefixed second mass value (Ms), in case said measured mass value is lower than said predefined threshold value (Mfs); - monitoring said temperature values, in case said measured mass value is lower than said prefixed second mass value (Ms); - performing the following steps in case said measured mass value is greater than said prefixed second mass value (Ms) for a prefixed time limit (ts) and said measured mass value is greater than a third mass value which is equal to a mass value able to operate a first resistor placed inside said first dehumidifying tank: ∘ checking if a second resistor and/or a ventilation means placed inside said second dehumidifying tank is/are operating ∘ and switching on an electric valve for operating (22, 23) said second dehumidifying tank and said first resistor coupled with said first dehumidifying tank. - starting and setting at zero data relating to said load cell; - monitoring temperature values detected by a first temperature sensor placed inside said first dehumidifying tank, by a second temperature sensor placed inside a second dehumidifying tank and by a third temperature sensor placed inside said load cell and monitoring said mass value detected by said load cell; - comparing said mass value measured by said load cell with said predefined threshold value (Mfs); - sending an alarm signal, in case said measured mass value is greater than said predefined threshold value (Mfs); - data processing for computing a first mass value and for comparing said first mass value with at least one prefixed second mass value (Ms), in case said measured mass value is lower than said predefined threshold value (Mfs); - monitoring said temperature values, in case said measured mass value is lower than said prefixed second mass value (Ms); - performing the following steps in case said measured mass value is greater than said prefixed second mass value (Ms) for a prefixed time limit (ts) and said measured mass value is greater than a third mass value which is equal to a mass value able to operate a first resistor placed inside said first dehumidifying tank: ∘ checking if a second resistor and/or a ventilation means placed inside said second dehumidifying tank is/are operating ∘ and switching on an electric valve for operating (22, 23) said second dehumidifying tank and said first resistor coupled with said first dehumidifying tank. ∘ checking if a second resistor and/or a ventilation means placed inside said second dehumidifying tank is/are operating ∘ and switching on an electric valve for operating (22, 23) said second dehumidifying tank and said first resistor coupled with said first dehumidifying tank.