HVAC Systems

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HVAC Systems
2015-04-01 03:14:43
HVAC Systems

HVAC Systems, Repair, Controls Questions
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  1. Air conditioning works on the basic principles of refrigeration, which are ? 2 points
    • Fluids absorb heat when changed from a liquid to a gas. 
    • Fluids give off heat when changed from a gas to a liquid.
  2. The three major principles of physics that take place within the refrigerant cycle are:
    • evaporation
    • condensation
    • heat transfer.
  3. The laws of heat transfer state the following:
    • Heat always flows from an area of higher temperature to an area of lower temperature. 
    • The greater the difference in temperature, the faster heat flows 
    • Heat continues to flow until both temperatures are equal.
  4. Evaporation is the process ?
    is the process of changing a liquid into a vapour.

    any liquid can be changed into a gas or vapour by adding heat 
  5. Condensation is the process of ?
    is the process of changing a vapour into a liquid. 

    any gas or vapour can be changed into a liquid by removing heat
  6. Latent Heat of Vaporization
    • is the amount of heat required for a change in physical state. 
    • The Latent Heat of vaporization is the amount of heat required to change a liquid into a vapour, without changing the temperature of the vapour.
  7. Latent Heat of Condensation
    amount of heat removal required to change a vapour into a liquid without changing the temperature of the liquid.
  8. Pressure and Temperature Relationship - 2 points
    • If the pressure acting on a liquid is increased, the boiling point of the liquid also increases.
    • If the pressure acting on a liquid is decreased, the boiling point of the liquid also decreases.
  9. R12 - name threads as well
    • CFC type refrigerant (dichlorodifluoromethane) 
    • non-toxic, non-flammable, non-corrosive and odourless.
    • Container Colour: White
    • External Threads
  10. R134a - name threads & oils as well.
    • HFC type refrigerant (tetrafluoroethane) 
    • does not deplete the ozone layer. 
    • non-toxic, non-corrosive, non-flammable and odourless. 
    • Container Colour: Light Blue
    • Internal Threads - designed to prevent leakage and prevent cross contamination of refrigerants.
    • Polyalkylene Glycol (PAG)
    • Polyol ester Oil (POE) - good choice for when topping up an A/C system's lubricant level.
  11. Compressor - Primary, Secondary Purposes.
    Separates the high-pressure side and the low pressure side. 

    Primary Purpose: to draw the low-pressure and low-temperature vapour from the evaporator and compress this vapour into high-temperature, high-pressure vapour.

    Secondary Purpose: is to circulate or pump the refrigerant through the A/C system under the different pressures required for proper operation.
  12. Fixed Displacement Compressors
    used in air conditioning cycling clutch systems to control the pressure and temperature at which the refrigerant system operates.
  13. Clutch Cycling - Clutch Operation
    • Clutch not engaged, pulley freewheels meaning refrigerant is not flowing.
    • Clutch engaged - power transmitted from the pulley to the compressor shaft by the clutch drive plate - refrigerant is flowing. 
  14. Condenser purpose
    • is to condense or liquify the high-pressure, high-temperature vapour coming from the compressor. 
    • having a higher temperature than the surrounding air, the condenser allows the hot refrigerant condense from vapour back to liquid.
  15. Evaporator - purpose, function, location.
    • Primary Functions: are to cool, dehumidify and clean the air entering the passenger compartment.   
    • refrigerant coil mounted in series of the thin cooling fins. 
    • usually located beneath the dash board or instrument panel. 
    • the evaporator receives low-pressure, low-temperature refrigerant from either a fixed orifice tube or an expansion valve in the form of an atomized (or droplet) spray. 
    • the evaporator serves as a boiler or vaporizer to boil the refrigerant.
  16. Accumulator-Dryer where is found, components purpose.
    • is to separate and trap any liquid droplets of refrigerant that may have passed through the evaporator without evaporating. 
    • Contains a Desiccant 
    • has an inlet tube -connected to the evap. outlet. The outlet of the accumulator is connected via tubing hoses to the suction side of the compressor.
    • found in an air conditioning system equipped w/ an orifice tube metering device.
  17. Purpose of the Desiccant
    dries the refrigerant by absorbing any moisture that may have entered the system.
  18. What valves are located - typically near the top of the accumulator-dryer assembly ? (R12 & R134a)
    Schrader Type service valve (R12) or Quick Service Valve (R-134a)
  19. Receiver-Dryer - purpose
    • is a storage tank for the liquid refrigerant from the condenser 
    • uses a TEV to control refrigerant flow into the exap. 
    • as mesh screen helps filter out any debris or contaminants in the refrigerant.
  20. Expansion Valve or Orifice Tube (TEV or TXV - Thermostatic Expansion Valve)
    • located in the refrigerant line between the condenser outlet and the evap. inlet.
    • separates the high-pressure side and low pressure side of the system. 
    • (Operation) the TEV regulates refrigerant flow to the evaporator to prevent evaporator flooding or starving.
  21. TXV uses a ________ to modulate between actual pressure and measured temperature. This allows the valve to _______________.
    • equalizer.
    • meter the refrigerant more accurately.
  22. Pressure Cycling Switch
    • is used to prevent ice from forming on the evaporator core. 
    • this switch cuts off the compressor when the pressure and the temperature of the evaporator reach a predetermined setting below the freezing point of water. 
    • also prevents compressor operation when air conditioning system pressure drops too low.
  23. You can recognize orifice tube systems by _______________________.
    the accumulator assembly mounted on the outlet line of the evaporator.
  24. You can recognize expansion valve systems by _________________________.
    by receiver-dryer mounted on the outlet line from the condenser.
  25. Temperature Blend Door
    is used to control the airflow through the heater core. This is a variable-position door.
  26. Outside air/recirculation door/valve
    is used to control which air inlet (outside or recirculation) is used.
  27. 3 Classifications of temperature control are:
    • manuel 
    • semi-automatic 
    • electronic automatic temperature control (EATC)
  28. Latent Heat definition of definition.
    is the amount of heat required for a change in physical state.
  29. CFC/HCFC releases to the atmosphere can cause:
    • Ozone Depletion 
    • global warming 
    • acid rain
  30. Global Warming is a result of:
    heat-trapping gases in the atmosphere.
  31. Heat quantity is measured in which imperial unit ?
  32. Which substance changes state from a liquid to a vapour, wht is the latent heat ?
  33. Superheat in a A/C evaporator is directly controlled by:
    thermal expansion valve
  34. Refrigerant entering the compressor is an A/C system should be in which state ?
  35. The only oem approved oil for used R134a systems is:
    Polyalkaline Glycol
  36. The temperature at which a liquid boils directly affected by:
    System Pressure
  37. What are two important functions for an air conditioning compressor ?
    Circulation & Pressurization
  38. The valve used to control suction pressure in a variable displacement compressor is called ?
    Compressor Control Valve
  39. The purpose of a receiver - drier in an A/C system is to:
    Absorb Moisture and Store Refrigerant.
  40. Purpose of the Accumulator/Dryer is an orifice tube system is to:
    Filter, vaporize, and absorb moisture from refrigerant.
  41. The function of the condenser is to:
    change vapour to a liquid
  42. The function of the evaporator is to:
    change liquid to a vapour
  43. The evaporator's temperature in a clutch cycling orifice tube A/C system is controlled by:
    pressure cycling switch
  44. The purpose for evacuating an A/C system is to remove:
    air & moisture
  45. When should oil level checks be done on an automotive A/C system ?
    after doing repairs that involve opening the system.