HVAC System Controls part 2 1 Heater controls Electrical: – Wiring diagrams – Blower controls Conventional circuits Multiplex circuits – Actuators Vacuum controls Electronic actuation – Network communication Bus connectors

Radiator Heater Hoses Heater Control Valve Heater Core Blower Warm Air Water Pump Heater Controls OUT IN Heat controlled with Cable-Operated Heater Control Valve Air Mix Control Damper Heater Core Heat controlled with Blend Door OLD NEW 2

Electrical Diagram Symbols 3

Electrical Diagrams 4

5 Blower Controls Conventional circuitry

Blower Controls 6 Resistor Block Located in HVAC case for cooling Resistor block is normally bypassed during high speed operation

7 Blower Controls Blower power module: transistor controlled by PWM signal from blower controller Infinite speeds Reduced wiring

8 Blower Controls

Current Flow in a Solid State Relay A solid state relay is also called a transistor. When a specific signal is applied to the transistor’s base, it allows current flow. Signal from ECU or control circuit Current flows only when the appropriate signal is applied to the base Base Emitter Collector 9

Current Flow in a Solid State Relay B+ PCM PCM grounds transistor base to energize blower motor 10 B+

Current Flow in a Solid State Relay B+ PCM Blower control can be on either side of circuit and allows infinite blower speeds B+ 11

Integrated Controller Blower Motor A/C ECU HTRALT FL Main Battery B SI GND From HTR Relay IK3 M Blower Motor Blower Motor Controller A/C Control Assembly SI GND+B VM Field Effect Transistor (FET ) Integrated Controller Motor Assembly Control Circuit Separate Controller Brush Motor OLD NEW 12

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14 Blower Speed Control Multiplex circuitry

Actuator Operation: vacuum controls 15

Actuator Operation: vacuum solenoids 16

Electronic Actuator Operation 17 Electronic systems provide the ability of self-diagnostics

18 Electrical Controls RheostatPotentiometer

Actuator Operation 19 Variable Resistor (Potentiometer)

Multiplex Systems 20 Communication between inputs and outputs in a multiplex system utilizes a specialized harness called a bus. Communication within the network is a series of voltage pulses.

BUS Connector Advantage With Bus Connectors Pulse-type Servo-motors BUS Connector Communication/Driver IC A/C ECU Communication IC CPU One 3-wire harness Without Bus Connectors Servo-motors Four 5-wire harnesses A/C ECU Drive IC CPU Drive IC A/C MMMM MMMM Bus connectors allow a manufacturer to utilize interchangeable actuators. Bus connectors are specific to a location and interpret bus communication for actuator operation. OLD NEW 21

BUS Connectors BUS Connectors with built-in communication/driver ICs allow the use of pulse-type servo-motors and require less harness wiring. Bus Connector With Bus Connectors Pulse-type Servo-motors BUS Connector Communication/Driver IC A/C ECU Communication IC CPU One 3-wire harness A/C MMMM Note: If the color-coded connectors are not matched to the correct servo- motors, the wrong motors will operate. IC 22

BUS Connectors Bus Connector Network buses are not repairable and damaged harnesses or connectors require bus replacement 23