1. Always Learning

2. HVAC System Electrical and Electronic Controls:
CHAPTER 14
HVAC System Electrical and Electronic Controls:
Theory, Inspection, Diagnosis, and Repair

3. Understand the relationship between volts, amperes, and ohms.
OBJECTIVES
After studying Chapter 14, the reader will be able to:
Understand the relationship between volts, amperes, and ohms.
Understand the circuits required for electrical units to operate.
Be aware of the types of HVAC circuit problems that may be encountered.
Be familiar with the procedure used to locate and repair HVAC problems.
Complete the ASE tasks related to electrical or electronics diagnosis and repair.

4. KEY TERMS Alternating current (AC) Ampere (amp) Ampere-turns
Belt-lock strategy
Body control module (BCM)
Controller area network (CAN)
Circuit breaker
Complete circuit
Conductor
Diagnostic trouble code (DTC)
Diode
Direct current (DC)
Dynamic resistance
Electronic control module (ECM)
Electrostatic discharge (ESD)
Fuse
Fusible link
Ground
Ground circuit
High-resistance circuit
Malfunction indicator light (MIL)
Multiplex
Ohm (Ω)
Open circuit
Parallel circuit
Positive temperature coefficient (PTC)
Pulse width modulation (PWM)
Relay
Scan tool
Schematic
Series circuit
Smart control heads
Smart motors
Static resistance
Volt (V)
Watt
Wiring diagram

5. INTRODUCTION
At one time, the electrical control circuit for the heat and A/C system was rather simple; a few checks with a test light located most problems.
Today’s systems have evolved into complex electronic circuits with connections to the electronic control module (ECM) and/or body control module (BCM) .
The HVAC control head on some vehicles features touchpanel operation and a digital readout of in-car and outside temperature and can call up diagnostic trouble codes (DTCs) .

6. SAFETY TIP
The high-voltage circuits in hybrid vehicles must be treated with respect and caution, and this includes every bright orange wire and the HV battery pack. Section 1.8 should be reviewed before testing or working on the HV electrical components.

7. Three measurable aspects of electricity concern a technician:
BASIC ELECTRICITY
Three measurable aspects of electricity concern a technician:
Volts (V)
Amperes (amps)
Ohms (Ω)

8. BASIC ELECTRICITY SYSTEM COMPONENTS
Most electrical systems have five major components:
Power source
Protection devices
Control devices
Connecting wires
Output devices

9. BASIC ELECTRONICS
SENSORS
CONTROL MODULE
ACTUATORS
MULTIPLEX AND CAN SYSTEMS

10. HVAC CIRCUITS
POWER SUPPLY
COMPRESSOR CLUTCH CIRCUIT
BLOWER MOTOR CIRCUIT
ELECTRONIC CONTROLLED VARIABLE COMPRESSOR
COOLING FAN CIRCUIT
HYBRID VEHICLE CIRCUITS
CLIMATE-CONTROLLED SEATS

11. ELECTRICAL CIRCUIT PROBLEMS
OPEN CIRCUITS
HIGH-RESISTANCE CIRCUITS
SHORTED CIRCUITS
GROUNDED CIRCUITS
EMI, RFI

12. MEASURING ELECTRICAL VALUES
MEASURING VOLTAGE
SOURCE VOLTAGE
MEASURING RESISTANCE
MEASURING AMPERAGE
INTERPRETING MEASUREMENTS
ADVANCED TESTING METHODS, ELECTRONIC SELF-DIAGNOSIS
OBD-II
SCAN TOOLS
VARIABLE COMPRESSOR DIAGNOSIS
ECM FLASHING
ACTUATOR MOTOR CALIBRATION

13. TECH TIP
A test light can be used to check continuity of a DC motor by connecting the light between the motor leads and B. Connect the other motor lead to ground, and the light should light up. Next, rotate the motor at least one revolution, and the light should stay on. If the light goes out, there is a bad winding in the motor, and the motor should be replaced.

14. TECH TIP
Ohm’s law includes a formula that compares the relationship of the three major electrical values. If you know two of the values, you can easily calculate the third. This becomes handy if one value, resistance, is hard to measure but two other values, volts and current, can be measured easily.

15. TECH TIP
Most DMMs are self-ranging and give a reading of any resistance value within their ability. They also indicate in range Ω, kΩ, and MΩ.

16. TECH TIP
A small inductive pickup is commonly called an amp probe or current probe ; the sensing portion is small enough to clamp over a single wire from a harness. This allows a fairly quick and easy method of checking a circuit’s current flow.
Measuring the resistance of a clutch coil can be difficult, but measuring voltage and clutch current flow can be easy. If the voltage measures at 13.9 V and there is a 3-amp current draw, solenoid resistance is 13.9 / 3 = 4.6 Ω.

17. ELECTRICAL SYSTEM REPAIR
ELECTRICAL COMPONENT REPLACEMENT

18. TECH TIP
If using a shrink tube , slide a piece of tube, about ½ inch longer than the splice, over the wire before connecting it in step 2. Slide the tube away from the connection while soldering it. After soldering the connection, slide the tube to the proper location and heat it to shrink the tube to lock it in place. If using tape , make sure the tape is wrapped tightly and smooth and looks neat.

19. SUMMARY
HVAC technicians should be able to measure voltage, current flow, and circuit resistance.
HVAC technicians should be able to check for open, shorted, grounded, and high-resistance circuits.
Components that have the correct current flow usually have the correct voltage and resistance.
Electrical system repair includes wire replacement, wire splicing, connector/terminal replacement, and component repair or replacement.
Electronic systems usually include self-diagnosis and the use of scan tools to read diagnostic trouble codes (DTCs).

20. REVIEW QUESTIONS
Electrical force is called ____________ ; a(n) ____________ is the amount of electrical current flow; and ____________ are the units of electrical resistance.
Most electrical circuits include a(n) ____________ ____________ , ____________ ____________ , ______________ ____________ , ____________ , and ____________ ____________ .
Electric wires transmit electricity through the ____________ while the current flow is contained by the ____________ .
The strength of a compressor clutch coil is determined by the number of ____________ ____________ and the amount of ____________ ____________ .

21. REVIEW QUESTIONS
The diode at the clutch coil protects the electronic ____________ ____________ from voltage ____________.
An in-vehicle sensor is a type of ____________ that increases resistance when the temperature ____________ .
A(n) ____________ converts a(n) ____________ signal into an electrical signal.
If the ECM finds a problem in an electronic control system, it will turn on the ____________ ____________ ____________ and set a(n) ____________ ____________ ____________ .
Most actuator motors contain a(n) ____________ ____________ so the ECM will know the motor position.

22. REVIEW QUESTIONS
A smart control head contains ____________ for motor ____________ .
____________ allows a pair of wires to be used for more than one ____________ .
A strategy that prevents potential compressor problems from damaging the accessory drive belt is called ____________ ____________ strategy, and it works when the compressor ____________ ____________ signal shows a slower speed than the engine.
A(n) ____________ ____________ is when electric current leaves the wire it is supposed to be in to go to another wire, and a(n) ____________ ____________ is when electric current leaves the wire it is supposed to be in and goes to ground.

23. REVIEW QUESTIONS
A blown fuse is often an indication of ____________ ____________ flow.
An ECM can be damaged by ____________ if you touch one of the terminals with your finger.
A clutch coil should have at least __________ __________ at the B terminal when the engine is running.
A ____________ ____________ allows you to read DTCs, the signals from the sensors to the ECM, and the signals from the ECM to the actuators.
The best way to clear a DTC without erasing the memory of other electronic circuits is to use a(n) ____________ ____________ .

24. 1. Which of the following is the unit for electrical pressure?
CHAPTER QUIZ
1. Which of the following is the unit for electrical pressure?
Amp
Ohm
Volt
Watt

25. 2. Most automotive electrical systems use AC current.
CHAPTER QUIZ
2. Most automotive electrical systems use AC current.
True
False

26. CHAPTER QUIZ
3. A fusible link is usually four wire sizes ____________ than the wire used in that particular circuit.
Larger
smaller
Either a or b
Neither a nor b

27. CHAPTER QUIZ
4. Which of the following is considered an output device in an ATC system?
Compressor clutch
Blower motor
Both a and b
Neither a nor b

28. 5. Which of the following is monitored by a sensor in an ATC system?
CHAPTER QUIZ
5. Which of the following is monitored by a sensor in an ATC system?
Ambient temperature
In-vehicle temperature
Sunload
All of these

29. CHAPTER QUIZ
6. Electrical mode doors in an ATC system usually have a feedback sensor string connected to them.
True
False

30. CHAPTER QUIZ
7. Which of the following test instruments can be used on any automotive electrical circuit?
Test light
Ohmmeter
Analog multimeter
DMM

31. 8. Modern electronic circuits can be damaged by ____________ .
CHAPTER QUIZ
8. Modern electronic circuits can be damaged by ____________ .
electrostatic discharge
excess heat
rough handling
Any of these

32. 9. Which of the following is true concerning ohmmeters?
CHAPTER QUIZ
9. Which of the following is true concerning ohmmeters?
Ohmmeters are self-powered.
Ohmmeters can be used on live circuits.
Ohmmeters cannot be used to check continuity.
None of these are true.

33. 10. A rule of thumb for clutch coil resistance is ____________ .
CHAPTER QUIZ
10. A rule of thumb for clutch coil resistance is ____________ .
10 ohms
3 to 5 ohms
about 5 amps
5 to 10 ohms

34. a. check for trouble codes b. clear the trouble codes
CHAPTER QUIZ
11. A vehicle with an ATC system has heater and defroster operation, but the A/C is not working properly. To diagnose this problem, the technician should ____________.
a. check for trouble codes
b. clear the trouble codes
Which is correct?
A only
B only
Both A and B
Neither A nor B

35. 12. An example of a short circuit is a ____________ .
CHAPTER QUIZ
12. An example of a short circuit is a ____________ .
clutch coil with a resistance of 0.5 Ω
burned-out lightbulb
burned wire with bad insulation that touches ground
Any of these

36. CHAPTER QUIZ
13. The blower motor runs on high speed only. This indicates a faulty ____________ .
high-blower relay
resistor bank
Switch
None of these

37. CHAPTER QUIZ
14. The vehicle overheats because the cooling fan does not operate. This could be caused by a ____________.
faulty fan relay
bad blower motor ground connection
faulty blower motor
Any of these