Heating and Air Management Systems Inspection and Diagnosis

1. Always Learning

2. CHAPTER 13 Heating and Air Management Systems Inspection and Diagnosis

3. OBJECTIVES After studying Chapter 13, the reader will be able to: • Inspect a heater system to determine whether there is proper coolant flow through the core. • Inspect a heater system to determine whether there are any coolant leaks. • Check the operation of mechanical and vacuum controls and determine whether there are any faults. • Complete the ASE tasks related to heater system diagnosis. • Complete the ASE tasks related to air management system diagnosis.

4. Air bleeds Cable adjustment Calibration Corrosion Cycling Diagnostic trouble code (DTC) Electrolysis Erosion On-board diagnostics (OBD) Quick-connect coupling KEY TERMS

5. INTRODUCTION • Problems in the heater system or air management system can show up with improper operation of the components or during the HVAC system inspection. • Further tests can be done to determine the exact causes of these problems.

6. HEATER INSPECTION • COOLANT CIRCULATION CHECKS • HEATER CORE LEAK CHECK • REMOVE AND REPLACE HEATER CORE • BLEEDING AIR FROM CORE • DEFROSTER CHECKS

7. REAL WORLD FIX • The heater core in the 1994 Pontiac Bonneville (109,000 miles) was leaking, and the core had been replaced four different times at another shop. The cooling system was checked for combustion leaks and none were found. A new, top-quality core was installed, but the vehicle returned in two and a half months with the same problem, a leaking core. • Following advice from a technical service bulletin (TSB), the technician thoroughly flushed the cooling system to remove abrasive silicates from the old antifreeze. A new heater core was installed, and the system was filled with new antifreeze and water coolant. This repair fixed the problem.

8. TECH TIP • An infrared thermometer makes coolant circulation checks easier, safer, and more accurate. Simply point the unit at the heater hoses and read their temperature.

9. TECH TIP • Some vehicles have a coolant restrictor at one of the heater core connectors. This restrictor orifice can become plugged.

10. TECH TIP • Low coolant level can cause poor coolant flow through the heater core of some vehicles. Check to make sure that the system is filled with a 50/50 water/antifreeze mix.

11. TECH TIP • Use care when removing a hose from a heater core connection; do not force hoses on or off a connector. The hose will probably stick to the connector, and the twisting and pulling to try to remove it can easily damage the connector. On systems that use quick-connect couplings, use the proper tool to release the coupling and then pull the coupling straight off the heater core connector. Damage to the coupling or connector can necessitate expensive repairs. • A less expensive option to repair a leaky heater hose using quick connectors is to remove the damaged hose from the connector by cutting the ferrule. If using an abrasive wheel, wear eye protection. Be careful not to cut too deeply and damage the nipple. Carefully remove the ferrule and old hose and clamp a new hose to the connector.

12. TECH TIP • Heater core flushing is described in Chapter 18, but flushing is not effective if the core is completely plugged. Some sources suggest filling a plugged core with ammonia, but this is not recommended because ammonia can eat away some heater cores very rapidly. The best repair is to replace the core, and many heater cores are mounted inside of the evaporator–heater case.

13. REAL WORLD FIX • The 1985 BMW 535i (237,000 miles) had a strange problem. The heater worked great at idle speeds, but there was no heat while driving down the road. The coolant was changed, and the system was refilled using an Air Lift to ensure no air locks. The heater control valve was checked. The screen was clean, and the plunger moved in and out. • Following advice, the technician rebuilt the mono valve using the proper repair kit. This 10-minute job fixed this problem.

14. TECH TIP • It is possible for the leak to be located at the heater hose connection that allows coolant to run along the connector and into the case. For this reason, and also because heater core replacement is usually difficult and expensive, it is recommended that an additional check be made to confirm that the core is bad. This test can be made with the core still in place or on the bench. If bench testing, the core can be placed underwater and the air bubbles from a leak will show the exact location of the leak.

15. REAL WORLD FIX • The 1995 Pontiac Grand Am had a leaking heater core so it was replaced. The problem reoccurred three more times; each time an OEM or ACDelco core was used. A heater core ground wire was added during the third replacement, but this did not help. • Following advice, the technician checked the engine electrical grounds. One of the grounds was found to be missing the star washer and was not completely tight. Installing the star washer and properly tightening the mounting bolt fixed this expensive problem.

16. TECH TIP • When replacing a heater core, check the coolant; if the coolant is dirty or old, change it. Many heater core leaks are caused by dirty or worn-out coolant. • After filling a cooling system, it is a good practice to run the engine until the thermostat opens and add additional coolant as it becomes necessary. Thermostat opening is indicated by the upper radiator hose becoming warm. During the waiting period, turn on the heater to full heat or defrost, which should open any water valves, and feel for a warm air discharge, which indicates that the core is full of coolant. If the air does not warm up, bleed the air from the core by loosening the uppermost heater hose at the core. A “burp” of air indicates the release of an air lock. When coolant starts coming from the loosened hose, replace the hose and retighten the connection.

17. TECH TIP • Gurgling noises can be caused by an air lock in the heater core. One method of removing the air lock is to remove the coolant recovery reservoir hose from the radiator filler neck, attach a vacuum pump to the filler neck, and pull a vacuum on the coolant. • Early failure of a heater core could be caused by a faulty starter ground connection; perform a starter ground voltage drop test. • If a redundant heater core ground strap is needed, connect it to the heater core and engine or starter ground.

18. TECH TIP • In cases of poor heat output, some techs reconnect the heater hoses to reverse the flow through the core, and sometimes the heat output increases.

19. TECH TIP • When replacing a rear-mounted heater core, the length of the hoses and the placement of the core make it difficult to bleed the air out of the core and lines. Some heater cores are mounted in a location that is higher than the radiator cap. If the connections are at the top of the core, which is the normal location, it is a good practice to fill the core with coolant before installing it.

20. REAL WORLD FIX • The 1989 Dodge Caravan had no heat from the front heater with good heat output from the rear unit. If the hose to the rear unit was clamped off, there was good heat output from the front unit. • It was discovered that a restrictor should be located in the hose to the rear unit. Installation of a restrictor fixed this problem.

21. TECH TIP • Some cooling system service machines evacuate all the air out of a cooling system using a vacuum pump. A check is then made to see if the system is leak-free and will hold the vacuum. A valve is then turned so coolant is pulled in to fill the cooling system. The entire procedure takes about 5 or 6 minutes. (See Chapter 18.)

22. HVAC AIR FILTER REPLACEMENT • In many vehicles, filter replacement is a simple matter of opening the access panels and removing and replacing the filter element. • With some vehicles, parts such as a portion of the instrument panel or the center console must be removed.

23. TECH TIP • A dirty cabin filter can restrict HVAC airflow. Failure to replace a charcoalmedia filter at the proper interval can cause odor problems. A “wet sock” odor during wet weather is an indication of a dirty charcoal filter.

24. TECH TIP • The life of a cabin filter depends on the filter location, whether it filters outside air or in-car air, how the vehicle is used, and where it is driven. Vehicles that are driven on dusty, dirt roads or used to transport cats or dogs will usually require more frequent filter changes.

25. REAL WORLD FIX • The 1988 Buick had poor airflow coming from the ducts. The blower sounded normal at all speeds, but the airflow was not correct for the different speeds. The vacuum servos all seemed to be working properly, and the temperature cable and its door were moving. • Inspection showed that the evaporator core was covered with oily debris. Replacement of the leaking evaporator core fixed this problem.

26. REAL WORLD FIX • The 1993 BMW 525i (213,000 miles) had a problem of poor air discharge. The blower motor and air control doors seemed to be working properly. The technician’s information did not indicate that this vehicle had a cabin filter. • Following advice, the technician checked and located a very plugged cabin filter. A filter replacement fixed this problem.

27. TECH TIP • Caution should be exercised when pulling, pushing, or probing wires to prevent the unexpected. At least one case of a technician accidentally triggering the air bags has been reported. On many cars, the control head can be partially disconnected and moved out far enough from the instrument panel to get to the cables or vacuum selector valve and hose connections behind it.

28. TECH TIP • Many vehicles with electric-actuator-operated blend doors require a calibration for the motor to determine proper door position. The HVAC calibration procedure is described in the vehicle service information or technical service bulletins (TSBs).

29. REAL WORLD FIX • The 1994 Taurus A/C system was recharged, and the compressor was operating normally with good pressures, but it would not switch from heat to A/C. • On inspection of the blend door and motor, signs of an earlier repair for the same problem were found. Someone had cut a hole into the housing and manually moved the blend door to full heat. At the customer’s request, the technician moved the door to full cold. It is expected that this vehicle will have a temperature control problem when the weather turns cool.

30. AIR MANAGEMENT SYSTEM CHECKS • Most air management system problems are related to the blower motor operation and the air doors not moving to the proper position. • The basic styles of door control are as follows: • Manual, using levers and mechanical cables • Vacuum switches, hoses, and motors • Electronic actuators and ATC or SATC using electric-solenoid-operated vacuum motors or electronic actuators

31. AIR MANAGEMENT SYSTEM CHECKS • BLEND DOOR OPERATION • CABLE CONTROL SYSTEM CHECKS AND ADJUSTMENTS • VACUUM CONTROL SYSTEM CHECKS

32. TECH TIP • A fairly accurate test for whether the blend door is operating properly is to clamp off the heater hose. If the air register discharge temperature drops more than a few degrees (some technicians use 5°F or 3°C as the cutoff point), you know the heated air is mixing in, probably from faulty door operation.

33. REAL WORLD FIX • The 1996 Ford Explorer (58,000 miles) stays on full heat all the time. The rest of the system seems to operate okay. Following advice and working through the glove compartment, the technician removed the blend door motor and determined that the operating shaft of the blend door was broken. • This blend door was replaced from under the hood by recovering the refrigerant, removing the evaporator, and removing the blend door from a new plenum assembly. The operating shaft had to be altered slightly in order to install it into the old plenum, but it performed satisfactorily after installation. Experienced technicians often develop shortcuts for certain jobs. These usually speed the job and save the customer money.

34. TECH TIP • It is also a good idea to check OEM TSBs; at least one vehicle model’s manufacturing process left plastic material that blocked complete door movement.

35. TECH TIP • Many technicians give priority of the door adjustment relative to their geographic location and climate. In areas that have cold winters, make sure the door “thunks” when moved to full heat; customers in these areas are more sensitive to lack of heat output. In areas that have hot summers, make sure the door “thunks” when moved to full cool; customers in these areas are more sensitive to lack of A/C.

36. REAL WORLD FIX • The 1992 Pontiac Bonneville (109,000 miles) HVAC system stayed on floor/defrost no matter where the controls were set. The technician was not sure how the doors operated, but he did not hear a vacuum leak. • Following advice from other technicians, the under-hood vacuum lines were inspected, and the plastic vacuum storage canister was found to be cracked. Replacement of this item fixed this problem.

37. TECH TIP • A tight-fitting piece of rubber hose or metal tube can be used to splice plastic lines.

38. TECH TIP • In the past, with rubber hoses it was possible to kink or pinch a line closed to shut off vacuum flow. This practice should be avoided with modern, hard plastic lines because the kink can cause a break and later failure. Hard plastic hoses should be isolated by disconnecting them and plugging the opening. Rubber vacuum hoses can be squeezed closed using pliers.

39. REAL WORLD FIX • The 1987 Ford LTD (115,000 miles) A/C system worked properly until you accelerated; it would then switch to full heat and low blower speed. It switched back when you let up on the gas. The ATC temperature sensor had been replaced, but this did not help. The system worked properly if a manual vacuum pump was attached to the system. • Following advice, the technician reinspected the vacuum check valve, and found it to be faulty. Replacement of the check valve fixed this problem.

40. TECH TIP • Vacuum leaks can also be detected using an ultrasonic leak detector or smoke machine. The ultrasonic tester can “hear” a vacuum leak and indicate its location. The smoke machine pumps machine-made smoke into the vacuum circuit so you can see the smoke escaping through the leak.

41. TECH TIP • If a vacuum is generated but it bleeds off rapidly , a small leak is indicated. Check the diagram to determine whether a vacuum bleed is contained in that part of the circuit; if so, this might be a normal condition. • If a vacuum cannot be generated , a leak in the hose or actuator is indicated. • If a vacuum is generated but the actuator does not operate , a kinked or plugged hose or faulty motor is indicated. In either case, move the vacuum pump directly to the actuator connection and retest.

42. REAL WORLD FIX • While driving the 1993 Dodge Caravan at cruise speeds with the A/C on, the system will start discharging all of the air out of the defroster ducts. It also does this under a hard acceleration. The vacuum storage tank and all of the vacuum lines under the hood have been checked and are okay. The vacuum check valve and control head have been replaced, but this did not help. • Following advice, the mode door actuator was tested and found to have an internal leak. Replacement of this vacuum motor fixed this problem.

43. SUMMARY • Many heater problems are caused by leaks or poor coolant circulation. • Heater core replacement varies greatly between different vehicle models. • When coolant is changed, all of the air must be bled from the heater core. • Cabin filter replacement varies greatly between different vehicle models. • Various checks and adjustments are used to ensure proper operation of the air management system doors and actuators.

44. REVIEW QUESTIONS • Wet carpet and excessive window fogging are signs of a heater ______________ ______________ . • Early heater core failure can be caused by ______________ or ______________ resulting from ______________ coolant. • Poor heater output can be caused by ______________ engine ______________ or ______________ through the heater core. • When a vehicle is operating, ______________ heater hoses should be ______________ . • The hose connections at the heater core of some modern vehicles use ______________ ______________ connectors that can require a(n) ______________ ______________ to disconnect them.

45. REVIEW QUESTIONS • A heater core can be checked for leakage by testing it to see if it will hold either a(n) ______________ or ______________ . • A(n) ______________ ______________ can prevent a heater core from filling with coolant. • An improper blend door adjustment can cause reduced ______________ or ______________ from the HVAC system. • When a control cable is replaced, the ______________ should be checked. • A(n) ______________ ______________ is indicated if an actuator will not hold a vacuum.

46. CHAPTER QUIZ 1. Technician A says that faulty heater operation can be caused by a faulty engine cooling system. Technician B says that a complaint of insufficient heat can be caused by someone not filling a cooling system properly. Who is correct? • A only • B only • Both A and B • Neither A nor B

47. CHAPTER QUIZ 2. Technician A says that a heater core leak can be the result of the coolant wearing a hole through the core. Technician B says that a core leak can be caused by chemical action eating a hole through the core. Who is correct? • A only • B only • Both A and B • Neither A nor B

48. CHAPTER QUIZ 3. Technician A says that the heater core inlet hose is connected to the water pump inlet. Technician B says that the heater inlet hose is often bigger than the outlet hose. Who is correct? • A only • B only • Both A and B • Neither A nor B

49. CHAPTER QUIZ 4. Insufficient heat output from a heater can be caused by a(n) ______________ . • plugged core • faulty thermostat • air lock • Any of these

50. CHAPTER QUIZ 5. Technician A says that faulty cable adjustments can cause improper heat and A/C operation. Technician B says that a broken vacuum hose can do the same thing. Who is correct? • A only • B only • Both A and B • Neither A nor B