1. Truck Trailer Refrigeration Maintenance
CHAPTER 17
Truck Trailer Refrigeration Maintenance
Instructor Name: (Your Name)

2. Learning Objectives
List components checked and maintained in a routine PM service of a refrigeration unit
Describe item that must be checked while servicing a diesel engine
Accurately check and adjust engine coolant strength
Describe refrigeration maintenance
List steps required to perform a compressor pump down
List steps required to perform a low side pump down

3. Learning Objectives
Describe the procedure used to replace a filter dryer
Explain evacuation techniques
Describe leak testing procedures
Describe soldering and brazing techniques
List structural item that should be checked during a PM

4. Engine Lubricating system
Warm engine to operating temp before draining
Have large enough drain pan, approximately 16.9 quarts
Replace engine oil filter on every oil change
Replace drain plug fill with proper quantity of oil, check the engine oil dipstick
Run unit, shut down, check level again and adjust if necessary

5. Engine Oil Drain Plug and Filter

6. Fuel filter Replacement
Remove primary and secondary filters
Do not prime prior to installation, unfiltered fuel can damage injection pumps
Tighten secondary filter until gasket contacts, tighten additional half turn
Install primary filter, spin on until just before gasket contacts
Operate the prime pump until bubbles surround the top of primary filter

7. Fuel filter Replacement (continued)
Tighten the primary filter until gasket contacts, tighten additional half turn
Start engine and look for potential leaks

8. Fuel Filter

9. Bleeding The Fuel System
Fill fuel tank
Crack bleeder screw on injection pump
Operate manual hand valve quickly air bubble are replaced by bubble free fuel from bleeder valve, this may take several minutes
Tighten bleeder screw while continuing to operate hand pump
Secure hand pump
Start engine, allow to operate until engine runs clean. This will ensure all air is out of system and alternator is not heavily charging. If it is allow it to recharge batteries or hook up external charger and charge batteries

10. Bleeder Screw and Prime Pump

11. Air Filters Two styles used, older oil bath and dry element
Oil bath are serviceable
Dry element use a disposable element
Many manufacturers use a air inlet restriction gauge on the intake system
Replace filter when indicator the red signal is in view with engine off
Make certain all clamps are tight and fit correctly
Reset air inlet restriction indicator after filter is replaced

12. Air Filter and Inlet Restriction Indicator

13. Engine Coolant Replacement
Warm engine to operating temp and open drain cock on engine block
Run clean water in top of radiator or expansion tank until clear water is draining from engine block
Inspect all hoses and clamps
Remove tension from water pump belt and inspect the water pump
Pressure test radiator cap
Pre mix 50/50 solution of antifreeze and de-mineralized water

14. Engine Coolant Replacement (continued)
Close drain cocks on engine block
Fill system and warm the engine with the radiator cap on loosely. This will allow trapped air to escape the system. Top off system as necessary and secure the radiator cap
Note: Always comply with environmental regulations in your area for properly disposing of coolant

15. Defrost System Defrost system should be checked on every service
Run refrigeration unit until box temperature is at or below 38⁰F (3.3⁰C)
Depress the manual defrost switch
The unit should shift from cool mode to defrost mode
If unit fail to go into defrost mode consult service manual for defrost cycle checkout procedures
Defrost air switches that sense air pressure on the inlet and outlet of evaporator coil to initiate defrost mode are commonly used

16. Defrost Air Switches

17. Defrost Air Switch Check
Remove all sensing tubes electrical connections from the air switch
Connect ohm meter across switch terminals
Connect magnehelic gauge to the high pressure side of switch
Raise the pressure of the magnehelic gauge until switch closes, as indicated by ohm meter.
The gauge reading, in inches or mm of water indicate the set point
If switch does not have continuity, pressurize the gauge to the specifications found in the service manual

18. Defrost Air Switch Check (continued)
Turn adjusting screw clockwise until switch closes and indicated by ohm meter
Repeat test several times to ensure setting is correct
Remove test equipment and hook up electrical connections.
Install sensing tubes to their original positions. The black hose to the air switch side marked black and the clear hose to the side marked clear

19. Defrost Air Switches Test Setup

20. NOTE:
Thermo King units use color coded sensing tubes. Carriers differentiate tubes by referring one as the high pressure and the other as the low side pressure. Testing and adjusting a Carrier air defrost switch is identical to the procedure previously described, with the exception of the switch settings. Always refer to the appropriate service manual for correct air switch specifications.

21. Testing Refrigerant Level
The operating pressures are for units operating on R-12, see service manual for pressures of system being tested
Operate system in cool mode., there should be at least 150 psi discharge pressure
Suction pressure and box temp are about equal
The ball should be floating in the receiver tank

22. Complete Recharge of Refrigeration System
Evacuate the system
Connect manifold gauge set to unit and mid seat the service valves
Connect refrigerant cylinder on scale and connect to manifold gauge set, note weight of cylinder
Open refrigerant cylinder liquid valve and discharge hand valve on manifold gauge set
Watch scale and stop when specified amount of refrigerant enters system

23. Complete Recharge of Refrigeration System (continued)
If feed stops before required amount enters system, close discharge gauge valve and cylinder liquid valve.
Open the suction hand valve on gauge set and vapor valve on the cylinder
Start system and run at high speed cool, vapor will be drawn in by compressor
Set gauge valve so the refrigerant is flowing at 30psi higher then the system suction pressure
Watch the scale and close valves when the required weight of refrigerant has entered the system

24. Manifold Gauge Connections

25. Manifold Gauge Connections (continued)

26. Partial Recharge of Refrigeration System
Connect manifold gauge set
Connect refrigerant tank to center hose of gauge set
Open tank in vapor position and purge center hose
Lower box temperature to 0⁰F (-18⁰C) or cover evaporator coil with test bag
Start unit with thermostat set to -20°F (-29°C)
Cover condenser until discharge pressure reaches 150 psi (1034 kPa)
Add refrigerant to suction side until the receiver sight glass ball floats

27. Compressor Oil Check Follow manufacturers recommendations
Run unit 15 to 20 minutes in high cool
Check oil level in the compressor oil level sight glass
Normally oil level should be one quarter to half way up window

28. Compressor Pump Down Connect manifold gauges, mid seat service valves
Run unit high speed cool minutes
While unit is running front seat suction valve
When suction pressure at inches (51-68 kPa) shut unit down. Compressor must hold vacuum before proceeding
If compressor has residual refrigerant it may be necessary to repeat procedure

29. Compressor Pump Down (continued)
With compressor in vacuum front seat the discharge service valve
Using manifold gauge bleed some refrigerant from the high side to the low side of system until low side has a 1 to 2 psi kPa) positive pressure
When compressor is opened to atmosphere it is important to have positive pressure or foreign material may be drawn onto the compressor
Note: Never operate unit with discharge valve closed, severe damage could occur
With compressor pumped down compressor oil can be changed

30. Compressor Pump Down (continued)
Place drain pan under oil drain plug and remove plug
Remove oil fill plug. Replace both plug seals
Install the oil drain plug
Add the quantity as specified in the service manual
Install the oil fill plug
With service valves front seated connect vacuum pump to gauge set and pull compressor into deep vacuum and check that it holds for at least 5 minutes
Back seat service valves, unit is now ready to return to service

31. Compressor Oil Drain Plugs

32. Low Side Pump Down
Install manifold gauge set, run system 5 to 10 minutes
With system high speed cool front seat receiver outlet valve
When suction pressure reaches 15 to 20 inch (51-68 kPa) vacuum, shut unit down. Unit must hold vacuum before proceeding
Using manifold gauge bleed some refrigerant from the high side to the low side of system until low side has a 1 to 2 psi kPa) positive pressure
Service work on low side of system can now be performed

33. Evacuation Process
Prior to evacuation ensure all refrigerant has been removed
Connect refrigerant hoses to refrigeration unit.
Run vacuum to deep vacuum prior to opening service valves to test the service equipment
Mid seat service valves
Run vacuum pump until a 2,000 micron reading is obtained
Turn of vacuum pump and seal from system, wait a few minutes to ensure vacuum holds

34. Evacuation Process (continued)
Restart vacuum pump, allow to run until 500 microns are reached on vacuum gauge. Close off vacuum pump and turn off. Vacuum must hold for 5 minutes, loss of vacuum indicates moisture or leaks in system
Refrigerant can be drawn into system while in deep vacuum, note weight of refrigerant cylinder

35. Soldering and Brazing Safety
Work in well ventilated work space
Wear protective (non flammable) clothes
Wear proper eye protection
Maintain all soldering and brazing equipment
Remove all flammable materials prior to soldering or brazing

36. Most Common Alloys for Silver Brazing
Sil-Fos 5
Sil-Fos 6
Sil-Fos 15
Phoson +

37. Six Steps for Leak-Proof Silver Brazed Joints
Tight filament of joint
Clean joint contact area
Correct use of brazing flux on the join
Stress relief on joint while brazing
Correct heating and alloy flow techniques
Final cleaning

38. Six Steps for Leak-Proof Silver Brazed Joints (continued)
Joint fitment- Cut squarely, Debur the cut, Joint clearance no more than .005” (0.127 mm)
Joint Cleaning- Clean completely of all oil, grease, rust or oxides, clean inside with solvent or tubing brush, clean outside with 320 grit sanding cloth
Joint Fluxing- Flux must not get inside the system, fit tubes part way then apply flux
Joint Stress Relief- support so it will not hinder expansion and contraction

39. Tools and Procedures For Brazing Tubing Joints

40. Six Steps for Leak-Proof Silver Brazed Joints (continued)
Joint Heating
Heat with number 5 oxyacetylene tip
Air propane and air acetylene can be used on tubing up to 1 inch
Use neutral flame
Start heating ½ to 1 inch from end of fitting
Heat evenly around circumference of tubing
Bulk of heat should be concentrated on the fitting
Do not stop moving the torch, fitting can quickly over heat

41. Six Steps for Leak-Proof Silver Brazed Joints (continued)
Joint Heating (continued)
When flux becomes clear apply alloy to the joint seam
If temperature is correct alloy will flow into joint
Once enough alloy has been applied pass torch at base of joint to expel any gas in joint
Final Cleaning- Use wet rag or brush to remove al flux on outside of joint

42. Heating Techniques

43. Heating Techniques Vertical Down Silver Brazing Joint
Vertical Up Silver
Brazing Joint

44. Heating Techniques Horizontal Silver Soft Solder Brazing Joint

45. Heat Sinks
When soldering or brazing around components that may be damaged by heat, a heat sink should be used. A heat sink will absorb damaging heat that can destroy components such as vibrasorbers and service valves. If a heat sink is not available use a wet rag wrapped around vibrasorber will draw enough heat to prevent damage.

46. Heat Sinks

47. Summary
A PM on a refer unit includes engine, fuel system, compressor, drive belt, refrigeration system, Glow plugs, and structural checks
Engine oil and filters should be changes according to manufacturers recommendations
Fuel filters should be changed during engine service
Bleeding purges air from the fuel system
Air cleaners filter all combustion air
Belt tension and condition should be checked at all PM services

48. Summary Glow plugs preheat combustion air to aid starting
Engine coolant should be checked periodically
The coolant system should be flushed when dirty
The purpose of the defrost cycle is to remove accumulated ice from the evaporator coil
The defrost air switch is responsible for initiating a defrost cycle
The defrost termination switch is responsible for terminating the defrost cycle
Refrigerant levels should be checked during every PM

49. Summary
The compressor oil should be checked whenever a refrigerant leak is suspected or when components have been serviced or replaced
A low side pump down can be performed whenever service work is required on low side of system. This procedure allows service of all components downstream of receiver to compressor to be serviced without removal of refrigerant
To remove refrigerant from compressor, a compressor pump down is required

50. Summary
The compressor oil can be changed or service work can be performed on compressor or suction service valve when the compressor is pumped down
The evacuation process removes air and moisture from the refrigeration system after it has been opened
Always follow safety precautions when soldering or brazing refrigeration components
Causing inert gas to flow through joints will prevent copper oxide from forming on inside of tubing
To produce a trouble-free silver brazed joint always follow the six steps

51. Summary
Follow correct heating procedure for the type of joint you intend to braze
Soft solder requires the same preparation as silver brazing; the difference is the melting point of the solder
The structural integrity of the unit should be examined on a PM. This would include examining the engine and fuel tank mounts, visual inspection of unit; checking cleanliness of coils; checking evaporator drainage; and inspecting the defrost damper door system