AUT 136 Automotive HVAC

1. AUT 136Automotive HVAC Chapter 9 Heating Systems

2. OBJECTIVES After studying Chapter 9, the reader should be able to: • Understand how the common automotive heating system works. • Explain what parts make up the heating system. • Understand how heater temperature is controlled.

3. INTRODUCTION • As previously mentioned, the heating system resembles a small version of the engine’s cooling system. • Some people consider the heater the most efficient part of the vehicle because it uses waste heat to warm the interior. • The heating system is made up of the heater core, hoses, and, in some systems, a control valve.

4. FIGURE 9-1 The main parts of a vehicle’s heating system are the heater core, blower, heater hoses, and in some cases heater valve. (Courtesy of Everco Industries) INTRODUCTION

5. OPERATION • The inlet hose to the heater core connects to an outlet near the engine thermostat, or an area of the engine with the hottest coolant. • The outlet hose from the heater core runs to a connection near the inlet of the engine’s water pump, the area with the lowest coolant pressure. • When the engine runs, coolant flows through the engine’s water jackets, past the thermostat, and through the heater core. • The heated coolant warms the heater core and the air passing through it

6. OPERATION FIGURE 9-2 Some heater systems use a valve (9) that can shut off the flow of hot coolant to the heater core (2). (Courtesy of Stant Manufacturing)

7. FIGURE 9-3 A heater control valve can be located at any of the positions shown. OPERATION

8. OPERATION • Engine-Off Heater Operation • Electric and Hybrid Vehicle Heating Systems

9. FIGURE 9-4 This hybrid vehicle has a pump/bypass that can pump hot coolant through the heater core (b, bottom) when the engine is shut off. During engine operation, the bypass valve (b, top) allows normal circulation. (Courtesy of Toyota Motor Sales USA, Inc.) OPERATION

10. FIGURE 9-4 (CONTINUED) This hybrid vehicle has a pump/bypass that can pump hot coolant through the heater core (b, bottom) when the engine is shut off. During engine operation, the bypass valve (b, top) allows normal circulation. (Courtesy of Toyota Motor Sales USA, Inc.) OPERATION

11. FIGURE 9-5 The two PTC, positive temperature coefficient, heater elements help warm the heater core of this hybrid vehicle. (Courtesy of Toyota Motor Sales USA, Inc.) OPERATION

12. FIGURE 9-6 Heat is transferred from the hot coolant flowing through the water tubes to warm the air flowing through the fins of the core. HEATER CORE • The heater core is a heat exchanger much like the condenser, evaporator, and radiator. • Heat transfers from the coolant, to the fins, and to the air passing through the core. • As with other heat exchangers, there is a large area of fin-to-air contact to allow sufficient heat transfer and air flow.

13. FIGURE 9-7 The critical dimensions needed when replacing a heater core. (Courtesy of Four Seasons) HEATER CORE

14. FIGURE 9-8 Two examples of the many shapes and sizes of heater cores. (Courtesy of Four Seasons) HEATER CORE

15. FIGURE 9-9 Heater hose uses reinforced rubber construction (a) and is available in straight or molded (b) shapes. (Courtesy of Veyance Technologies, Inc.) HOSES

16. FIGURE 9-10 Some vehicles use quick-connect couplings for the heater hose connections. The hose is merely slid firmly onto the connector to make the connection. It should be disconnected carefully using a suitable tool. (Courtesy of Four Seasons) HOSES

17. HOSES • Restrictors • Some systems include a restrictor to slow the coolant velocity as it passes through the heater core. • The restrictor can be part of the manifold fitting or the inlet heater hose assembly. • The major purpose of the restrictor is to slow the flow rate in order to reduce noise and internal heater core erosion.

18. CONTROL VALVES • Most heater control valves are on–off valves and are used to make the core either hot or cold. • Some valves are designed to modulate and adjust the flow so the core temperature can be controlled to all points between hot and cold. • Some valves allow a return flow, so the coolant still circulates, bypassing the core when the valve is shut off.

19. FIGURE 9-11 A heater control valve can be operated manually (a), by vacuum control (b), through a mechanical cable (c), or by a thermostatic element (d). (a courtesy of Four Seasons; b, c, and d are courtesy of Stant Manufacturing) CONTROL VALVES

20. FIGURE 9-12 The control panels for a vehicle with front and rear climate control systems. (Courtesy of Chrysler LLC) DUAL HEATING SYSTEMS • Many vehicles with rear A/C systems include a heater in the rear unit. • These rear units include a heater core and temperature-blend door

21. AFTERMARKET HEATING SYSTEMS • Before heaters became standard equipment, aftermarket heating systems were installed in many cars. • Today, these units are primarily designed for RVs, vans, and motor homes. • They are normally installed after the vehicle has been built, by shops that specialize in heating and A/C service or RV van conversion and repair.

22. FIGURE 9-13 This aftermarket heater assembly (a) contains a heater core (9) and blower (1–4). An exploded view is shown in (b). (Courtesy of Red Dot) AFTERMARKET HEATING SYSTEMS

23. SUMMARY • Heaters use hot coolant from the engine cooling system. • Some vehicles have engine-off heater operation using an electric pump and control valves. • The heater core resembles a small radiator, and it is connected to the engine by a pair of hoses. • Some vehicles use a coolant flow valve to control heater output temperature. • Some vehicles use dual heater systems; these can be OEM or aftermarket.

24. REVIEW QUESTIONS • The heater core inlet hose connects to the engine close to the _________, and the outlet hose is connected close to the water pump _________. • The heat from a vehicle’s heater comes from the engine _________. • A(n) _________ _________ heater core is made from a set of stamped metal plates. • Critical dimensions of a heater core include the _________, _________, and _________ of the core plus the _________ and _________ of the tubes.

25. REVIEW QUESTIONS • A hose clamp of good design will not _________ the hose, clamp completely _________ the hose, and compensate for _________ and _________. • Some modern heater hoses use _________-_________ couplings at the heater core. • Temperature of the air leaving the heater ducts is controlled by a(n) _________ that regulates the coolant flow through the core or by a(n) _________-_________ door. • Some vans will use _________ _________ systems to help warm up the rear compartment.

26. CHAPTER QUIZ • Two students are discussing the coolant flow through a heater core. Student A says that heated coolant enters the heater inlet hose close to the engine thermostat. Student B says the coolant from the heater core returns to the water pump outlet. Who is correct? • A only • B only • Both A and B • Neither A nor B

27. CHAPTER QUIZ 2. Two students are discussing the heater core. Student A says that a heater core is a heat exchanger much like a radiator. Student B says the coolant from the engine brings the heat to the heater core. Who is correct? • A only • B only • Both A and B • Neither A nor B

28. CHAPTER QUIZ 3. Two students are discussing heater hoses. Student A says that most hoses have an inside diameter of about one inch or larger. Student B says the heater core inlet hose is usually larger than the outlet. Who is correct? • A only • B only • Both A and B • Neither A nor B

29. CHAPTER QUIZ 4. Heater hoses are attached to the core using _________. • Clamps • quick-connect couplings Which is correct? • A only • B only • Both A and B • Neither A nor B

30. CHAPTER QUIZ 5. Two students are discussing the heater output temperature. Student A says that a valve is used to reduce coolant flow through the core when less heat is desired. Student B says that most modern systems use a blend-air door to control the heat/cooling output. Who is correct? • A only • B only • Both A and B • Neither A nor B

31. CHAPTER QUIZ 6. The control for most heater control valves is either a Bowden cable or mechanical. • True • False

32. CHAPTER QUIZ 7. Two students are discussing heater temperature control. Student A says that a control valve will be wide open when full heat is desired. Student B says the coolant control valve should go wide open if the vacuum line is disconnected. Who is correct? • A only • B only • Both A and B • Neither A nor B

33. CHAPTER QUIZ 8. An aftermarket heater system consists of _________. • a core • a blower • control switches • All of these