The invention relates to a method for operating a vehicle air-conditioning system in dependence on the difference between the temperature of the engine coolant at the inlet into the heating heat exchanger and the temperature of the air at the outlet out of the heating heat exchanger. The measured or estimated temperatures of the coolant at the inlet into the heating heat exchanger and of the air at the outlet out of the heating heat exchanger are checked to determine whether their values indicate fault states of components of the air-conditioning system.

The invention is to utilize one radiator instead of two to cool two separate vehicle cooling systems. The main embodiment is a single radiator cooling system that partitions the physical radiator into two separate surface areas that are dedicated for each of the two respective circuits. A processor can control an actuator that drives a screw and plunger mechanism to push and pull a plunger. The plunger separates the two surface areas so as the plunger is moved, a corresponding surface area is increased or decreased for a cooling circuit. An increase in the surface area can provide more cooling for that circuit as the fluid has more core area to travel through. Temperature sensors can provide data to a processor that can adjust the actuator to provide cooling relief to the circuit where its most required.

An object is to acquire a humidity of gas compressed by a compressor accurately, in a control system for an internal combustion engine that executes control concerning a water content in intake gas passing through an intercooler, based on an output signal from a humidity sensor. A humidity sensor is provided in an intake passage between a compressor and an intercooler. Therefore, a behavior of a humidity of gas that is compressed by the compressor and flows in the intake passage at an upstream side from the intercooler can be accurately grasped. The humidity sensor is desirably provided in the intake passage directly downstream from the compressor.

A control unit stores a correlation between a temperature difference T between an inlet temperature and an outlet temperature of a heat exchanger for cooling of cooling water, and the amount of thermal deformation occurring in the heat exchanger. At the time when the cooling water is supplied to the heat-exchanging flow path having the heat exchanger, the control unit refers to the temperature difference T and the correlation to obtain the volume of flow of the cooling water supplied to the heat-exchanging flow path so that the amount of thermal deformation is less than or equal to a threshold amount of thermal deformation set in advance.

A learning unit learns a difference between a detected value ECT and a detected value RCT when it is determined that the detected value ECT and detected value RCT are stable while an engine is at a stop. A diagnostic unit performs a fault diagnosis for the engine based on the difference between the detected value ECT and detected value RCT having been corrected through use of a learned value learned by the learning unit. Accordingly, a fault diagnostic system for an internal combustion engine and a fault diagnostic method for an internal combustion engine can be achieved in which accuracy in fault diagnosis for the internal combustion engine can be improved and an erroneous diagnosis can be restrained.

The invention is to utilize one radiator instead of two to cool two separate vehicle cooling systems. The main embodiment is a single radiator cooling system that partitions the physical radiator into two separate surface areas that are dedicated for each of the two respective circuits. A processor can control an actuator that drives a screw and plunger mechanism to push and pull a plunger. The plunger separates the two surface areas so as the plunger is moved, a corresponding surface area is increased or decreased for a cooling circuit. An increase in the surface area can provide more cooling for that circuit as the fluid has more core area to travel through. Temperature sensors can provide data to a processor that can adjust the actuator to provide cooling relief to the circuit where its most required.