The Refrigeration System

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The Refrigeration System
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PREPARATION

• Develop a consistent routine.
• Use Common Sense Approach
• Consult Service Manuals
• Cleanliness
• Safety

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CHECK THESE FIRST

• BELT TENSION
• COMPRESSOR CLUTCH OP
• COOLING FAN OP
• BLOWER MOTOR OP
• AIR FLOW FROM DUCTS
• REFRIGERANT CHARGE
• SERVICE VALVES
• LINES, HOSES, CONNECTIONS
• AMBIENT AIR TEMP

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Refrigerant

• A compound used in mechanical refrigeration
  systems
• Used to transfer heat
• R-134A used since 1996
• Contains no chlorine
• Many older systems can be converted to R-134A
• Available in 1lb 33lb
• Must have certification to purchase

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Molecular Structure
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Refrigerant Oil

• Lubricates compressor TXV
• Mineral oil in R12 systems
• Polyalkylene Glycol (PAG) oil in R134A systems,
  blue color (water based)
• Must maintain specific amount in system
• Never reuse old oil, add fresh oil

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Temp Pressure Relationship

• To keep Evap just above freezing (icing)
• Refrigerant temps pressures closely related
• Low side temp/ Evap
• High side temp/condenser

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Temperature-Pressure Relationship Chart

• Temp R134A Temp R134A Temp R134a
• 0 6.5 55 51.2 110 146.3
• 5 9.1 60 57.4 115 158.4
• 10 12 65 64 120 171.1
• 15 15.1 70 71.1 125 184.5
• 20 18.4 75 78.6 130 198.7
• 25 22.1 80 86.7 135 213.5
• 30 25.3 85 95 140 229.2
• 35 30.4 90 104.3 145 245.6
• 40 35 95 113.9 150 262.8
• 45 40 100 124.1
• 50 45.4 105 134.9

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A/C temperature testing

• True test of systems ability to cool
• Is normally measured at center outlet
• Procedure
• Run system _at_ med blower, engine _at_ 1500 rpm
• Engine warm let idle, blower low
• Measure temp _at_ center vent
• Should be 20 degrees reduction over incoming air

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A/C pressure testing MUST WEAR EYE PROTECTION!!!

• Manifold gauge set
• Low side gauge
• A compound gauge reads both pressure vacuum
• low side, blue hose

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A/C pressure testing

• High side gauge
• Measures pressure only
• High side, red hose

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A/C pressure testing

• Yellow center hose
• Hooked to service equipment
• Two hand valves control flow.
• Must be closed while testing
• All hoses are anti-blowback

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Test ports

• Quick connect
• Covered by protective caps, reduces slow leakage
• Special schrader valve

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Pressures - low side

• Reflects evap temp
• R12 systems run 25-35 psi
• R134a systems run 20-25psi

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Pressures - high side

• Reflects condenser temp
• All systems vary based on ambient temps
• R12 will typically run 150-250 psi
• R134a systems up to 300 psi

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TXVSystem
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Orifice Tube System
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NORMAL OPERATION 1

• Low-side gauge Normal pressure
• CFC-12 32-33 psig HFC-134a 30-31 psig
• High Side Gauge Normal Pressure CFC-12
  185-190 psig HFC-134a 204-210 psig

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INSUFFICIENT COOLING 2

• Low side Gauge Low Pressure CFC-12 15
  psig HFC-134a 12 psig
• High Side Gauge Normal Pressure CFC-12
  190 psig HFC-134a 208 psig
• Possible Causes Thermostat (icing) Low side
  restriction Moisture in system

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INSUFFICIENT OR NO COOLING 3

• Low Side Gauge Low or Very low Pressure
• CFC-12 18 psig
• HFC-134a 15 psig
• High Side Gauge Low Pressure
• CFC-12 130-135 psig
• HFC-134a 139-144 psig
• Possible causes Clogged TXV inlet screen, bad
  valve, Moisture in system

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INSUFFICIENT OR NO COOLING 4

• Low side gauge Low Pressure
• CFC-12 22 psig
• HFC-134a 20 psig
• High side gauge High to extremely High
• CFC-12 250 psig
• HFC-134a 281 psig
• Causes Restriction in High Side
• Temperature change present at restriction

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INSUFFICIENT OR NO COOLING 5

• Low side High Pressure
• CFC-12 44 psig
• HFC-134a 43 psig
• High side Low Pressure
• CFC-12 140 psig
• HFC-134a 150 psig
• Causes Bad Clutch, Bad compressor
• (compressor not turning normally mech... or
  electrical)

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INSUFFICIENT COOLING 6

• Low Side High Pressure
• CFC-12 40 psig
• HFC-1334a 38 psig
• High Side Normal Pressure
• CFC-12 170 psig
• HFC-134a 184 psig
• Causes Expansion Valve stuck open

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INSUFFICIENT OR NO COOLING 7

• Low Side High Pressure
• CFC-12 42 psig
• HFC-134a 37 psig
• High Side High to extremely High
• CFC-12 235 psig
• HFC-134a 263 psig
• Causes Air in system, Overcharge, overcharge of
  oil, Clogged condenser, Non op Fans, Engine
  overheating, Incorrect or contaminated refrigerant