1. CHAPTER 6 Moving Heat: Heating and Air Conditioning Principles

2. Objectives Understand heating and cooling loads.
After studying Chapter 6, the reader will be able to:
Understand heating and cooling loads.
Explain the ways to handle a heating load.
Explain the ways to handle a cooling load.
Describe the effect that compression and expansion have on the temperature of a gas.

3. Objectives Discuss heat transfer in the refrigerant system.
Describe the effect humidity has on the air conditioning system.
Explain the pressure and vacuum relationship in the air conditioning system.
Understand the basic function of the various air conditioning components.
Discuss the role of refrigerant in the system.

4. Objectives Explain the pressure verses temperature relationship.
Know the physical state, pressure, and temperature of the refrigerant in different areas of the refrigerant system.
Describe the nomenclature and function of the manifold and gauge set.
Identify the scaling of the low- and high-side gauges in English and metric units.

5. Objectives Calibrate a gauge.
Connect a manifold and gauge set into an automotive air conditioning system.
Perform a performance test on an automotive air conditioning system.

6. INTRODUCTION
Heating and air conditioning must follow the basic rules of heat transfer.
An understanding of these rules helps greatly in understanding the systems:
Heat always flows toward cold.
To warm a person or item, heat must be added.
To cool a person or item, heat must be removed.
Fuels can be burned to generate heat.
A large amount of heat is absorbed when a liquid changes state to a vapor.
A large amount of heat is released when a vapor changes state to a liquid.
Compressing a gas concentrates the heat and increases the temperature.

7. HEATING LOAD Heating load is the term used when we need to add heat.
SEAT HEATERS

8. COOLING LOAD Cooling load
describes the removal of heat, which is the purpose of air conditioners and evaporative coolers.
We need to move heat to a cooler location in order to handle a cooling load.

9. COMPRESSION HEATING
When we compress a gas into a higher pressure, we also increase the temperature of the gas.
CO2 SYSTEMS

10. EXPANSION COOLING
If we can raise the temperature of a gas by compressing it, we can lower the temperature if we allow it to expand.
Expanding a volume of gas spreads out the heat energy over a larger area and lowers its temperature.

11. Air Conditioning System Components
Compressor
Condenser
Receiver dryer/Accumulator
Metering device
Evaporator
Hoses and lines
Service valves

12. Heat Transfer in A/C Systems
The basic function of the automotive air conditioning system is to remove heat and humidity from the passenger compartment and transfer this heat to the outside air.
Heat is removed from the airflow by an evaporator.
Refrigerant is pressurized by the compressor and set onto the condenser.
Condenser acts like a radiator, removing heat from refrigerant.
The system uses two different operating pressures (high and low).

13. Air Conditioning and Humidity
Humidity increases the heat load on the refrigerant system.
Maximum refrigerant system performance and passenger compartment cooling is achieved by selecting Recirculation mode.
Moisture removed from the air steam passing through the evaporator will drain out of the duct system.

14. How is Cooling Achieved in the Air Conditioning System?
Cooling in the refrigerant system is achieved by the rapid expansion of refrigerant gas.

15. Basic Air Conditioning System Components
Compressor
Heart of the air conditioning system
Pumps refrigerant through the system
Contains a suction side (low-pressure vapor, cold) and a compression side (high-pressure vapor, hot)

16. Basic Air Conditioning System Components
Condenser
Heat exchanger
Change of state takes place
High-pressure vapor (hot) changes into high- pressure liquid (hot)

17. Basic Air Conditioning System Components
System uses either
Receiver dryer – high-pressure liquid side
Placed between condenser and metering device
Used with thermostatic expansion valve
Accumulator – low-pressure vapor side
Placed between evaporator and compressor
Used with fixed orifice tube

18. Receiver Dryers & Accumulators
To play, click the video screen.

19. Basic Air Conditioning System Components
Metering Device
High-pressure liquid changed into a low- pressure liquid
Hot on the high-pressure side, cold on the low-pressure side
Two basic types
Thermostatic expansion valve
Fixed orifice tube

20. Two Basic Air Conditioning System Designs
The Expansion Valve designs

21. Two Basic Air Conditioning System Designs
The Orifice Tube design.

22. Basic Air Conditioning System Components
Evaporator
Heat exchanger
removes heat from the air entering the passenger compartment (cold)
Change of state takes place
Low-pressure liquid changes into low-pressure vapor

23. Basic Air Conditioning System Components
Hoses and lines
Suction line
Low-pressure, cool vapor
Discharge line
High-pressure, hot vapor
Liquid line
High-pressure, hot liquid

24. Basic Air Conditioning System Components
Service valves
R-134a (HFC- 134a)
R-12 (CFC-12)

25. Refrigerant
The substance that flows through the refrigeration system is referred to as refrigerant.
The most important properties of a refrigerant are:
A refrigerant must not be explosive or flammable.
A refrigerant must not be hazardous and a leak should be easily detectable.
The refrigerant must be highly stable and allow for repeated use without decomposing or changing its properties.
The refrigerant must not cause damage to parts or materials used in the compressor or other components.
The refrigerant must vaporize easily in the evaporator.
The larger the latent heat value at the vaporization point of the refrigerant, the smaller the volume of refrigerant that will be required for circulation and the smaller the total size of the refrigeration system.
The critical temperature of the refrigerant must be higher than the condensation temperature of the system.
Evaporator pressure must be higher than atmospheric pressure.

26. Refrigerant R-134a
If the pressure of R-134a is high the temperature will also be high.
If the pressure is low the temperature will also be low.

27. Refrigerant R-134a
The following graph represents the relationship of pressure and temperature of R-134a.
The curved line on the graph is the change of state point of R-134a between a liquid and a gas under various pressures and temperatures.

28. Pressure verses Temperature Relationship
Temperature at which refrigerant vaporizes or condenses is the saturation temperature.

29. Pressures High Side Low Side Prevents refrigerant from boiling
Moves heat to the condenser
Pressurizes refrigerant back to the evaporator
Low Side
Sudden loss of pressure at the metering device
Allows refrigerant to absorb heat in the evaporator
Moves heat to the compressor for refrigerant pressurization

30. State of Refrigerant in the Air Conditioning Circuit
Thermostatic Expansion Valve (TXV) System.
A – Low pressure vapor
B – Low pressure liquid
C – Low pressure liquid and vapor
D – High pressure vapor
E – High pressure liquid
F – High pressure liquid and vapor

31. State of Refrigerant in the Air Conditioning Circuit
Fixed Orifice Tube (FOT) System.
A – Low pressure vapor
B – Low pressure liquid
C – Low pressure liquid and vapor
D – High pressure vapor
E – High pressure liquid
F – High pressure liquid and vapor

32. To play, click the video screen.
Touch and Feel Test
To play, click the video screen.

33. Refrigerant Temperature Pressure Chart

34. Manifold and Gauge Set Is the primary diagnostic tool
Used to measures high- and low-side air conditioning system pressures
Also used to connect A/C system to recovery, recycling, or charging stations

35. Gauge Scales (1 of 2) Low Side Compound gauge Vacuum down to 30 in.Hg
Pressure to 120 psig
Metric
Absolute kiloPascal (kPa)
1 psi = kPa

36. Gauge Scales (2 of 2) High Side Pressure only Up to 500 psig
kPa gauge or absolute
Must be calibrated periodically

37. Connecting Gauges R-134a (HFC-134a)
Close all valves on Gauge Manifold.
Remove caps.
Pull up on quick-release collar and connect hose to A/C line fitting.

38. Connecting Gauges Safety glasses, gloves, fender cover
Schrader valve – R-12 (CFC-12)
Close all valves.
Remove caps.
Connect hoses firmly.

39. Performance Test Protect engine with external fan
Connect manifold and gauge set
Set engine speed rpm
Set A/C on MAX (Recirculation mode)
Check gauges for typical pressures
Check high- and low-side lines
Test control devices per manufacturer

40. To play, click the video screen.
Performance Test
To play, click the video screen.

41. Summary
A heating load occurs when heat is desired; a cooling load calls for more cooling.
Heat is added by moving hot coolant to the heater core and blowing in-car air across the heater core.
Cooling can occur through evaporative cooling.
Most vehicle cooling uses mechanical refrigeration to move latent heat from the evaporator to the condenser.
Gases heat when they are compressed and cool when they expand.