CHAPTER
13
Truck-Trailer
Refrigeration
Equipment
Instructor Name: (Your Name)
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Learning Objectives
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Describe air circulation through the cargo area.
List three different forms of short cycling.
Explain the operation of the thermostat.
Describe the refrigeration unit operation.
Explain the reasons for pre-cooling trucks and
trailers.
 Explain loading procedures to ensure proper
circulation .
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Learning Objectives (continued)
 Describe cargo floor construction.
 Explain a pre-trip inspection.
 Describe the advantages of multi-temperature
refrigeration units.
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Trailer Refrigeration Unit
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System Components
 Engine- Typically a four cylinder diesel.
 Compressor- Range from 2 to 4 cylinder.
 Condenser- Dissipates heat from trailer to
ambient air.
 Thermostatic Expansion Valve- Fixed orifice,
externally equalized.
 Evaporator- Absorbs heat in the trailer.
 Microprocessor- Brain of unit. Controls all
aspects of refrigeration and heating process.
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Typical Refrigeration Engine and
Microprocessor
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System Components (continued)
 Box Temperature- The actual temperature in
the storage unit.
 Set Point- Optimum temperature to maintain
product.
 Thermostat- Sets the temperature that the
equipment will maintain.
 Refrigerant- Chemical used to absorb and
dissipate heat in the storage area.
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Trailer Refrigeration System Layout
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Trailer floor Construction
 Fabricated from
Aluminum
 Forms ductwork
under cargo for air
circulation
 Must be kept free
from debris that can
impede air flow
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Multi Temperature Refrigeration
Units
 May have up to three units.
 Each unit has its own evaporator and
thermostat.
 Unit can store fresh, frozen and dry goods
together.
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Multi Temperature Trailer
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Pre Cooling Products
 Product must be cooled to the holding
temperature prior to loading trailer.
 Trailer refrigeration equipment is designed to
maintain temperature of product not cool it
down.
 Pre cool the trailer prior to loading.
 Shut down refrigeration unit while loading to
prevent refrigerated air from escaping.
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Proper Loading Procedures
• Pallets must be loaded so skids allow air flow
fore and aft in trailer.
• Product must be kept away from walls to allow
air flow around all sides.
• Ample air space must be allowed between load
and ceiling.
• Air space must be left between cargo door and
cargo.
• Air space must be left between front bulkhead
and cargo.
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Proper Pallet Placement
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Proper Cargo Loading Technique
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Improper Loading of Cargo
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Short Cycling
 Cargo is blocking units discharge air flow.
 Cold air is routed back to air inlet.
 Thermostat thinks it has reached set point and
switches to heat mode.
 Warm air flow is blocked and routed back to
air inlet.
 Thermostat thinks it has reached set point and
switches to cool mode.
 Process continues over and over, “Short
Cycling.”
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Auto Stop/Start
 Auto stop/start used by most equipment today.
 Constant run mode still available.
 Constant run mode, unit cycles between heat and
cool mode.
 Auto stop/start mode, unit will shut down once set
point is reached and programmed parameters are
met.
 Programmed parameters- unit must run long enough
to charge battery and warm the engine.
 Unit stays off until box temperature reaches preset
temperature.
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Summary
 Microprocessors control all aspects of
refrigeration and heating cycles.
 Modern advances in technology allow
distribution to market fresh fruit and
vegetables any time of year.
 Loads must be pre cooled to remove residual
heat and humidity.
 The box must be pre cooled to remove residual
heat and humidity.
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Summary (continued)
 Correct loading is essential to product quality.
 Discharge air must be able to circulate freely
around all side of the product.
 Rising fuel costs have contributed to the
technology for auto stop/start.
 The auto stop/start feature is a huge financial
savings for the company using it , as well as a
way of conserving our natural resources.
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