Cpt 11 HVAC Inspection and Diagnosis

1. Cpt 11 HVAC Inspection and Diagnosis

2. OBJECTIVES After studying Chapter 11, the reader should be able to: • Inspect an HVAC system to determine whether it is operating correctly, and if not to make further tests to locate the faulty subsystem and the cause of the problem. • Check HVAC system temperatures and determine if they are correct. • Follow a logical procedure to locate the cause of a problem in an HVAC system. • Complete the Automotive Service Excellence (ASE) tasks related to HVAC inspection and test procedures.

3. After-blow module Comeback Diagnostic trouble code (DTC) Electronic evaporator dryer (EED) Functional test Groundout Technical service bulletin (TSB) Trouble tree Visual inspection KEY TERMS

4. INTRODUCTION • Except for preventative maintenance operations, HVAC system repair should begin with a systematic procedure to determine exactly what is wrong. • If trouble diagnosis is thorough and accurate, all problems can be located and repaired at the same time. • An important step in the early part of the diagnostic procedure is to ensure that there is a problem and, if there is, to determine which HVAC subsystem is at fault.

5. HVAC SYSTEM INSPECTION • HVAC system inspection, often called a visual inspection or a functional test, is the quickest way to locate obvious problems. • It also gives the technician a good idea of the overall condition of the system.

6. HVAC Visual Inspection You might find the problem right off the bat!

7. HVAC SYSTEM INSPECTION • A/C System Inspection • With the engine off, the under-hood checks are as follows: • Check the condition of the belts. • Check the tension of the belt by pushing against the center at a longer span. • Inspect the refrigerant hoses and lines for oily residue and damage. • While checking the hoses and lines, determine whether you are dealing with a TXV or OT system and whether an STV or a variable displacement compressor is used. • Check the compressor mounting bolts to make sure they are tight. • Check to make sure there is an air gap at the compressor clutch. • Check the electrical wires to the clutch, blower motor, and any A/C switches for good, tight connections and possible damage.

8. HVAC SYSTEM INSPECTION • Check any vacuum hoses between the intake manifold and bulkhead, looking for kinked, cracked, or loose hoses. • Check the condition of the radiator cooling fan, fan clutch or motor, and fan shroud. • Check the condition of the radiator and heater hoses, looking for swollen, soft, cracked, kinked, or leaky hoses. • If the engine and radiator are cool, remove the cap and check the appearance of the coolant, which should be clean and have a bright color. • Check the faces of the condenser and radiator core; they should be clean, with no restriction to air flow. There should be no apparent leaks.

9. HVAC SYSTEM INSPECTION • A drive belt should be replaced if it has any of the problems shown. (Courtesy of Dayco Products, Inc.)

10. HVAC SYSTEM INSPECTION • With the engine off, compressor clutch inspection includes a check for air gap between the clutch plate and pulley. The hub and compressor shaft should rotate smoothly, without runout of the clutch plate.

11. HVAC SYSTEM INSPECTION • Hose inspection can be difficult in tight quarters. • Check for cracks and cuts and squeeze the hose to check for hardening or excessive softness. • Squeeze the hose close to the ends to check for softening.

12. HVAC SYSTEM INSPECTION • With the engine off, the in-car checks are as follows: • Operate the blower switch through its various speeds while you listen to the fan and motor for unusual noises. • Move the temperature lever of mechanically operated doors to both ends of its travel. • With the engine running, the in-car checks are as follows: • Note the alternator charge indicator; it should show a normal charge level or voltage after the engine runs a short while. • Set the blower speed to high, move the function control to all of its positions, and note the air discharge. • Turn on the A/C to determine whether the compressor clutch engages and the compressor operates.

13. HVAC SYSTEM INSPECTION • With the engine running, the under-hood checks are as follows: • Make sure the compressor clutch is engaged and the compressor is running. • Disconnect the clutch to make sure it releases smoothly. • Feel the temperature of the A/C lines and hoses. • Feel the temperature of the heater hoses. If the engine is at operating temperature, both hoses should feel hot. • Check the drive belts. • Check the fan operation (if running). The fan should be turning smoothly, with good air flow. • Check the evaporator drain.

14. HVAC SYSTEM INSPECTION • With the engine running, compressor clutch inspection includes a rapid engagement as the clutch wire is connected. • A clean disengagement with no drag as the wire is disconnected. • Smooth and quiet pulley operation • Very little runout of the pulley.

15. HVAC SYSTEM INSPECTION • When a system is operating properly, the suction line to the compressor should be cool, and the discharge line should be hot to very hot (a). The liquid lines should also be hot (b)

16. PROBLEM DIAGNOSIS • A visual inspection often locates the exact cause of a problem. • It nearly always reveals the nature of the problem, showing in what area of the system the problem lies. • Diagnosis charts, also called trouble trees, help guide the technician through the procedure to locate the cause of a problem in the shortest time possible. • In most cases, they use a logical, systematic series of tests and checks to isolate the area causing the problem.

17. PROBLEM DIAGNOSIS • Note that some checks lead to further checks that are listed on the troubleshooting charts.

18. PROBLEM DIAGNOSIS • A thorough diagnostic procedure follows steps like these to locate and repair problems the first time a vehicle is worked on.

19. PROBLEM DIAGNOSIS • Most vehicle manufacturers recommend that problem-solving or troubleshooting procedures be done in an organized manner • Verify the Complaint • Determine Related Symptoms • Analyze Symptoms • Isolate the Concern • Determine Problem • Repair Problem • Confirm Repair

20. Chart (a) shows the most probable and possible causes of a group of problems. PROBLEM DIAGNOSIS

21. PROBLEM DIAGNOSIS • This chart shows the procedure for locating a noisy compressor problem. Chart (c) is a flowchart for locating an ATC problem.

22. HVAC SYSTEM PROBLEMS • System Odors • Some systems develop a musty, moldy smell, which is not really a fault of the system. • Some sources classify these odors into two types: • “Dirty socks/gym locker” odor, which has an organic cause • “Refrigerator, cement, or dusty room” odor, which is caused by chemicals • A foul smell from the A/C can be cured by spraying a cleaning solution or fungicide onto the evaporator to either clean it thoroughly or kill the bacteria.

23. HVAC SYSTEM PROBLEMS • An electronic evaporator dryer (EED)/after-blow module can be connected into the blower motor circuit. It will operate the blower motor after the system is shut off to dry the evaporator and prevent bacterial growth.

24. HVAC SYSTEM PROBLEMSNoise Problems • The causes of most HVAC noises are shown here.

25. SUMMARY • Technicians should understand the customer’s concern, and carefully check the HVAC system so that all problems are repaired the first time. • An HVAC system should be thoroughly inspected, including under-hood and in-vehicle inspections, with the engine off and again with the engine running. • A checklist is normally followed to prevent missing any items and also to show the customer. • The diagnostic and repair procedure normally follows a seven-step process. • Bad smell caused by fungus growth and noise are fairly common HVAC system problems.

26. REVIEW QUESTIONS • The goal of automotive technicians is to fix vehicle problems _________ the _________ _________. • HVAC system inspection normally begins _________ the hood with the _________ _________. • During the under-hood inspection, the technician should determine what _________ of _________ the vehicle has. • _________ _________ on a refrigerant hose or fitting can indicate a leak. • With the system off, there should be a(n) _________ _________ at the compressor clutch plate.

27. REVIEW QUESTIONS • The in-vehicle HVAC system checks include operation of the _________ and _________ _________ for air-flow control. • Compressor engagement is usually indicated by an audible _________. • An early step in determining how to make a repair is to check for _________ _________ _________. • _________ _________ will often lead the technician to the cause of many HVAC problems. • Many stinky HVAC system problems are caused by _________ _________ on the evaporator.

28. CHAPTER QUIZ • Technician A says that you should begin HVAC problem diagnosis with a thorough inspection. Technician B says that you can determine from the inspection what type of system you are dealing with. Who is correct? • A only • B only • Both A and B • Neither A nor B

29. CHAPTER QUIZ 2. Technician A says that sometimes nothing is wrong with a system when there is a complaint of insufficient cooling. Technician B says that you should begin diagnosing this complaint by checking the A/C system pressures. Who is correct? • A only • B only • Both A and B • Neither A nor B

30. CHAPTER QUIZ 3. Technician A says that while the compressor clutch is off, it’s OK if the pulley and clutch plate touch. Technician B says that too much air gap can cause clutch slippage during engagement. Who is correct? • A only • B only • Both A and B • Neither A nor B

31. CHAPTER QUIZ 4. Technician A says that oily residue on a hose can indicate a refrigerant leak. Technician B says that this residue is normal for most connections. Who is correct? • A only • B only • Both A and B • Neither A nor B

32. CHAPTER QUIZ 5. Technician A says that a quick check of A/C system operation is to feel the temperature of the suction and discharge lines. Technician B says that the suction line should be cold and the discharge line hot after a minute of system operation. Who is correct? • A only • B only • Both A and B • Neither A nor B

33. CHAPTER QUIZ 6. Technician A says that replacement of the fuse is the only repair necessary for a blown fuse. Technician B says that a blown fuse is caused by a system fault such as high resistance. Who is correct? • A only • B only • Both A and B • Neither A nor B

34. CHAPTER QUIZ 7. Technician A says that the first step in diagnosing a problem is to verify what the complaint is. Technician B says that a TSB can tell you the cure for some problems. Who is correct? • A only • B only • Both A and B • Neither A nor B

35. CHAPTER QUIZ 8. Technician A says that a misadjusted blend door can cause poor A/C operation. Technician B says that you can check this by clamping off a heater hose. Who is correct? • A only • B only • Both A and B • Neither A nor B

36. CHAPTER QUIZ 9. Technician A says that foul-smelling air from the A/C ducts is caused by bacteria growing on the evaporator fins. Technician B says that this problem can be cured by installing a control that operates the blower motor after the vehicle is shut off. Who is correct? • A only • B only • Both A and B • Neither A nor B

37. CHAPTER QUIZ 10. Technician A says that a refrigerant line groundout problem makes a whining noise at moderate speeds. Technician B says that knocking noises are a sure sign that the compressor has failed. Who is correct? • A only • B only • Both A and B • Neither A nor B