CAT C15 Fan Temperature Sensor Location and Function

The CAT C15 is a heavy-duty diesel engine that is used in various applications, such as trucks, buses, generators, and marine vessels. The engine has a cooling system that regulates the temperature of the engine components and prevents overheating. The cooling system consists of a radiator, a water pump, a thermostat, a fan, and various sensors and switches.

One of the sensors that is part of the cooling system is the fan temperature sensor, also known as the coolant temperature sensor (CTS). The CTS is a thermistor that measures the temperature of the coolant in the engine. The CTS sends a signal to the engine control module (ECM), which then controls the fan operation based on the coolant temperature and other inputs, such as the intake air temperature, the air conditioning pressure, and the manual override switch.

The CTS is located on the thermostat housing, which is typically a large, circular housing on the front of the engine. The thermostat housing contains one or two thermostats that control the flow of coolant between the engine and the radiator. The CTS is usually located near the top of the housing, next to the thermostat.

The CTS has two wires: a signal wire and a ground wire. The signal wire is connected to the ECM, and the ground wire is connected to the engine block. The CTS has a variable resistance that changes according to the coolant temperature. As the coolant temperature increases, the resistance decreases, and vice versa. The ECM converts the resistance into a voltage signal, which ranges from 0.2 V to 4.8 V. The ECM uses this signal to determine the coolant temperature and the fan operation.

The fan operation is controlled by a solenoid valve that is located on the fan hub. The solenoid valve receives power from the ECM, and either opens or closes the air passage to the fan clutch. The fan clutch is a device that engages or disengages the fan from the engine, depending on the cooling demand. When the solenoid valve is open, the air pressure is released from the fan clutch, and the fan is disengaged. When the solenoid valve is closed, the air pressure is applied to the fan clutch, and the fan is engaged.

The ECM determines when to engage or disengage the fan based on the coolant temperature and other inputs. The ECM has a fan-on temperature and a fan-off temperature, which are usually set at 205°F and 195°F, respectively. When the coolant temperature reaches the fan-on temperature, the ECM closes the solenoid valve and engages the fan. When the coolant temperature drops below the fan-off temperature, the ECM opens the solenoid valve and disengages the fan.

However, the fan operation is not only dependent on the coolant temperature, but also on other factors, such as the intake air temperature, the air conditioning pressure, and the manual override switch. The intake air temperature sensor (IAT) is located on the intake manifold, and measures the temperature of the air entering the engine. The air conditioning pressure switch (ACPS) is located on the air conditioning compressor, and measures the pressure of the refrigerant in the system. The manual override switch (MOS) is located on the dashboard, and allows the driver to manually turn on or off the fan.

The ECM uses these inputs to modify the fan operation according to the cooling demand. For example, if the intake air temperature is high, the ECM will lower the fan-on temperature and raise the fan-off temperature, to increase the cooling efficiency. If the air conditioning pressure is high, the ECM will close the solenoid valve and engage the fan, to reduce the pressure and prevent damage to the system. If the manual override switch is on, the ECM will ignore the other inputs and keep the fan engaged, to provide maximum cooling.

The following table summarizes the fan operation based on the different inputs:

Input Condition Fan Operation
Coolant Temperature Below fan-off temperature Fan disengaged
Coolant Temperature Above fan-on temperature Fan engaged
Intake Air Temperature High Fan-on temperature lowered, fan-off temperature raised
Intake Air Temperature Low Fan-on temperature raised, fan-off temperature lowered
Air Conditioning Pressure High Fan engaged
Air Conditioning Pressure Low Fan operation based on coolant temperature
Manual Override Switch On Fan engaged
Manual Override Switch Off Fan operation based on coolant temperature, intake air temperature, and air conditioning pressure

The fan temperature sensor is an important component of the cooling system, as it helps to regulate the engine temperature and prevent overheating. The sensor works in conjunction with the ECM and other sensors and switches to control the fan operation based on the cooling demand. The sensor is located on the thermostat housing, and has a variable resistance that changes according to the coolant temperature. The sensor sends a signal to the ECM, which then controls the solenoid valve and the fan clutch. The fan operation is also affected by the intake air temperature, the air conditioning pressure, and the manual override switch. The fan operation can be summarized by the table above.

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