D7E Track-Type Tractor Systems Electronic Control (HVAC System) Caterpillar


Electronic Control (HVAC System)
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1.1. Electronic Control Modules
2.2. Implement ECM
3.2. ECM Pull Up Voltage
4.2. ECM Pull Down Voltage
5.1. Pin Locations
6.1. Inputs
7.2. Sensors
8.3. Ambient Air Temperature Sensor
9.3. Evaporator Freeze Temperature Sensor
10.3. Air Conditioning Operator Temperature Control
11.3. Air Conditioning High and Low Pressure Sensor
12.2. Switches
13.3. Air Conditioning Mode Switch
14.1. Outputs
15.2. Condenser
16.2. Actuators
17.3. Water valve Actuator
18.1. Data Link
19.2. Cat Data Link
20.2. CAN Data Link

Electronic Control Modules

Implement ECM



Illustration 1g03307257


Illustration 2g01309473
ECM Connectors and Contacts

The Implement ECM determines actions that are based on input information and memory information. After the Implement ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the Implement ECM are connected to the machine harness by two 70 contact connectors (J1 and J2). The ECM sends the information to the AVSpare Electronic Technician (Cat ET) on the Cat Data Link.

Note: The ECM is not serviceable. The ECM must be replaced if the ECM is damaged. Replace the ECM if a failure is diagnosed.

ECM Pull Up Voltage

In order to aid in diagnostics of certain types of electrical circuits that are controlled by the ECM, an internal "pull up voltage" is connected to ECM switch and sensor signal input contacts. An above normal voltage is internally connected to the ECM signal input circuit through a resistor.

During normal operation, the switch or sensor signal will hold the circuit low or at a certain signal amplitude, however, circuit conditions such as a loss of power to the component, a disconnection, or an open circuit will allow the circuit to be pulled high by the ECM pull up voltage. This condition will result in an above normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 03 (voltage above normal) diagnostic code for the affected circuit.

The types of ECM input circuits that have pull up voltage present are:

  • Pulse Width Modulated (PWM) sensor input circuits

  • Switch to Ground Input switch input circuits

  • Active analog (voltage) input signal circuits

  • Passive analog (resistance) input signal circuits

ECM Pull Down Voltage

In order to aid in diagnostics of electrical circuits that are controlled by the ECM, an internal "pull down voltage" is connected to ECM switch to battery type input circuits.

During normal operation, the switch contacts that are allowing the connection to a voltage source will hold the circuit high. When circuit conditions such as a loss of power to the switch supply voltage, a disconnection in the switch circuit or an open circuit will allow the circuit to be pulled low by the ECM pull down voltage. This condition will result in a below normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 04 (voltage below normal) diagnostic code for the affected circuit.

Pin Locations

Table 1
Implement ECM Contact Description J1 Contact Descriptions(1) 
No.(2)  Type  Function 
14  Switch to Battery Input  Air Conditioning Switch 
21  Sensor Power Return  5V Sensor Return 
26  Switch to Ground Input  ECM Location 0 
30  Analog Input  Evaporator Freeze Temperature 
32  Switch to Ground Input  ECM Location Enable 
39  Battery Power Input  Battery + 
44  Sensor Power Output  8 V Sensor Supply 
45  Sensor Power Return  8 V Sensor Return 
46  Battery Power Input  Battery + 
47  Battery Power Input  Battery + 
50  Souring Driver Return  PWM Drivers 1 - 4 Return 
53  Analog Input  Ambient Temperature Sensor 
54  Souring Driver Return  PWM Driver 11-12 Return 
55  Souring Driver Return  PWM Driver 9-12 Return 
56  Sensor Power Return  Battery - 
57  Battery Return  Battery - 
60  Sourcing Driver Return  PWM Driver 5-8 Return 
69  Sensory Power Output  10V Sensor Supply 
70  Battery Return  Battery - 
(1) Contacts that are not listed are not used.
(2) The connector contacts that are not listed are not used.

Table 2
Implement ECM Contact Description J2(1) 
No.(2)  Type  Function 
Sourcing Driver Return  Load Return 1 
Sourcing Driver Return  Load Return 2 
Sinking Driver Output  Condenser Control Signal 
22  Return  Sensor / Driver Return 
33  PWM Input  Condenser Feedback 
34  PWM Input  High Pressure Switch 
35  PWM Input  Low Pressure Switch 
56  CAN Data Link +  CAN A Data Link + 
63  Return  Sensor Driver Return 
67  CAN Data Link +  CAN A Data Link + 
68  CAN Data Link -  CAN A Data Link - 
70  Can Data Link -  CAN A Data Link - 
(1) The ECM responds to an active input only when all of the necessary conditions are satisfied.
(2) The connector contacts that are not listed are not used.

Inputs

The machine has several different types of input devices. The ECM receives machine status information from the input devices and determines the correct output action that is needed in order to control machine operations based on memory and software parameters. The machine utilizes the following types of inputs: switch type and sensor type.

Switches provide signals to the switch inputs of the ECM. The possible outputs of a switch are listed: an open signal, a grounded signal and + battery signal.

Sensors provide an electrical signal to the ECM that constantly changes. The sensor input to the ECM can be one of several different types of electrical signals such as: pulse width modulated (PWM) signals, voltage signals and frequency input signals. Each possible input to the ECM is listed in the tables for the 70-pin connectors.

Inputs provide information to the ECM in the form of sensors or switches.

Sensors

Sensors provide information to the ECM about the intent of the operator or changing conditions. The sensor signal changes proportionally to the changing of operator input or changing conditions. The following types of sensor signals are used by the ECM.

Frequency - The sensor produces a signal and the frequency (Hz) varies as the condition changes.

Pulse width modulated - The sensor produces a signal. The duty cycle of the signal varies as the condition changes. The frequency of this signal is constant.

Analog - The ECM measures the voltage that is associated to a specific condition of the control.

Ambient Air Temperature Sensor



Illustration 3g03325780

The HVAC ambient air temperature sensor is a passive sensor located in the HVAC unit. The sensor creates a different resistance depending on the surrounding temperature. The variations in resistance cause a proportional variation in voltage. This voltage is measured at the ECM contact, and allows the ECM to determine the air temperature.

Evaporator Freeze Temperature Sensor



Illustration 4g03441376

The evaporator freeze temperature sensor is a passive sensor located in the sending air passage. The sensor creates a different resistance depending on the surrounding temperature. The variations in resistance cause a proportional variation in voltage. This voltage is measured at the ECM contact, and allows the ECM to determine the temperature of the evaporator.

Air Conditioning Operator Temperature Control



Illustration 5g03326001

The operator temperature control sensor monitors the signal from the temperature control knob on the HVAC panel. This knob sets the operators desired temperature in automatic mode and adjusts the water valve in manual mode. In either mode, the control panel generates a pulse width modulated signal from the knob and HVAC panel that corresponds to a desired temperature or water valve position. The duty cycle is proportional to the position of the knob.

Air Conditioning High and Low Pressure Sensor



Illustration 6g03723173

The air conditioning high and low-pressure sensors are active pulse width modulated sensors. The sensor detects the pressure of the air conditioning refrigerant and generates a proportional PWM signal. The ECM receives the PWM signal and determines if the compressor should be turned off.

Switches

Switches provide an open signal, a ground signal, or a +battery signal to the inputs of the ECM. Switches are open or closed.

  • When a switch is open, no signal is provided to the corresponding input of the ECM. This “no signal” condition is also called “floating”.

  • When a switch is closed, a ground signal or a +battery signal is provided to the corresponding input of the ECM.

Air Conditioning Mode Switch



Illustration 7g03325737

The air conditioning mode switch is a two pole switch. The switch has two positions that control the operation of the air conditioning. In the automatic position the ECM controls the operation of the air conditioning to maintain a specified cab temperature. In the manual position, the air conditioning is manually engaged. The ECM has two contacts that pertain to this switch, one signals the ECM the switch is automatic mode, the other signals the ECM the switch is in manual mode. These contacts will float to a high voltage state unless the switch is closed to that contact. When the switch closes to a contact, the contact is pulled to a low or ground voltage state.

Outputs

The ECM responds to decisions by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or the service technician.

Condenser



Illustration 8g03723230

The ECM controls the condenser through a control signal and a feedback signal. The ECM generates a signal to control the condenser, and receives a pulse width modulated signal feedback sensor.

Actuators

Water valve Actuator



Illustration 9g03091818

The water valve actuator controls the amount of heat that enters the HVAC system. When the water valve actuator is activated, the water valve opens and allows heat from the engine into the heater coils. The water valve is controlled by a pulse width modulated signal from the Machine ECM.

Data Link

Electronic communication between the Machine ECM, the Implement ECM, and the other control modules on the machine is conducted over data link circuits. The data link circuits allow the sharing of information with other electronic control modules. The data link circuits are bidirectional. The data link circuit allows the ECM to send information and to receive information.

The electronic communication system consists of two types of data link systems.

  • Cat Data Link

  • SAE J1939 (CAN) Data Link

The two types of data links are the main structure for communication between all of the control modules on the machine.

The SAE J1939 Data Link circuit is mostly used for faster operational communication between the control modules on the machine. The Cat Data Link is used for some of the internal communication that does not require the faster speeds and is used for communication with external devices such as the AVSpare Electronic Technician (Cat ET) service tool.

Cat Data Link

The Cat Data Link is an input/output of the ECM. The data link uses the connector for the service port in order to communicate with the AVSpare Electronic Technician. A data link connection is provided for the product link.

Note: The control for the product link provides a global positioning system for the machine.

The data link is bidirectional. The bidirectional link allows the ECM to input information and output information. The data link consists of the following parts: internal ECM circuits, the related harness wiring, the service tool connector and the connector for the product link. The Cat Data Link connects to the ECM at contact J1-10 (wire 893-GN(Green)) and contact J1-20 (wire 892-BR(Brown)).

  • The ECM receives commands from the Cat ET in order to change the operating modes. The Cat ET will read the service codes that are stored in the memory of the ECM. The Cat ET will clear the service codes that are stored in the memory of the ECM.

  • The ECM sends the input and the output information to the AVSpare ET.

CAN Data Link

A data link is required for communication with the service tool (Cat ET) and the electronic control modules as well as instrument clusters and other devices that use this communications protocol. The data link is not used in order to broadcast any diagnostic information.

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