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 Copyright 2014 Delmar, Cengage Learning
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 Copyright 2014 Delmar, Cengage Learning
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 Copyright 2014 Delmar, Cengage Learning Engine Oil Drain Plug and Filter
Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning Fuel filter Replacement (continued) Tighten the primary filter until gasket contacts, tighten additional half turn Start engine and look for potential leaks Copyright 2014 Delmar, Cengage Learning Fuel Filter
Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning Bleeder Screw and Prime Pump Copyright 2014 Delmar, Cengage Learning 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
Copyright 2014 Delmar, Cengage Learning Air Filter and Inlet Restriction Indicator Copyright 2014 Delmar, Cengage Learning 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 demineralized water Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning Defrost System Defrost system should be checked on every service Run refrigeration unit until box temperature is at or below 38F (3.3C) F (3.3F (3.3C) C)
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 Copyright 2014 Delmar, Cengage Learning Defrost Air Switches Copyright 2014 Delmar, Cengage Learning
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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning Defrost Air Switches Test Setup Copyright 2014 Delmar, Cengage Learning 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. Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning Manifold Gauge Connections
Copyright 2014 Delmar, Cengage Learning Manifold Gauge Connections (continued) Copyright 2014 Delmar, Cengage Learning 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 0F (3.3C) F (-18F (3.3C) C) or cover
evaporator coil with test bag Start unit with thermostat set to -20F (-29C) Cover condenser until discharge pressure reaches 150 psi (1034 kPa) Add refrigerant to suction side until the receiver sight glass ball floats Copyright 2014 Delmar, Cengage Learning
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
Copyright 2014 Delmar, Cengage Learning Compressor Pump Down Connect manifold gauges, mid seat service valves Run unit high speed cool 10-15 minutes While unit is running front seat suction valve When suction pressure at 15020 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
Copyright 2014 Delmar, Cengage Learning 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 6.9-13.8 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 Copyright 2014 Delmar, Cengage Learning 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
Copyright 2014 Delmar, Cengage Learning Compressor Oil Drain Plugs Copyright 2014 Delmar, Cengage Learning 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 6.9-13.8 kPa) positive pressure Service work on low side of system can now be performed Copyright 2014 Delmar, Cengage Learning
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
Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning
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 Copyright 2014 Delmar, Cengage Learning Most Common Alloys for Silver Brazing Sil-Fos 5
Sil-Fos 6 Sil-Fos 15 Phoson + Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning
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
Copyright 2014 Delmar, Cengage Learning Tools and Procedures For Brazing Tubing Joints Copyright 2014 Delmar, Cengage Learning 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 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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning
Heating Techniques Horizontal Silver Brazing Joint Soft Solder Technique Copyright 2014 Delmar, Cengage Learning 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. Copyright 2014 Delmar, Cengage Learning Heat Sinks
Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning 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 Copyright 2014 Delmar, Cengage Learning
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 Copyright 2014 Delmar, Cengage Learning
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