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City & Guilds 2079-11 F-Gas Category I Cheat Sheet

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Refrigeration Cycle & p-h Diagrams

  • 32% of exam
  • Compressor+condenser Expansion+evaporator Superheat vs sub-cool p-h diagram basics Leak-indicator components

Refrigerants, F-Gas & ODS Regs

  • 20% of exam
  • EU 517/2014 retained law CO2e = mass x GWP 2020 HFC service ban HFC phase-down quota 5-year record keeping

System Components

  • 20% of exam
  • TEV/TXV + filter drier Manifold gauges red/blue Liquid receiver + sight glass Zeotropic vs azeotropic blends Deep vacuum ~500 microns

Leak Detection & Repair

  • 5% of exam
  • Direct vs indirect methods 5g/year detector sensitivity 12/6/3-month check bands Fixed detector doubles interval 1-month follow-up check

Recovery, Recycling & Reclamation

  • 5% of exam
  • 80% cylinder fill limit Recycling vs reclamation AHRI 700 standard No venting, ever Separate cylinders per gas

Environmental Impact (GWP/ODP)

  • 5% of exam
  • GWP: CO2=1 reference ODP: R-11=1 reference HFC high GWP, zero ODP Montreal 1987 ozone treaty Kigali 2016 HFC phase-down

Safety & Legislation

  • 13% of exam
  • HASAWA 1974 general duty COSHH hazardous substances OFN for purge + testing Cardiac sensitisation risk Cold burns + asphyxiation

Quick Facts

  • Exam C&G 2079-11
  • Category Category I (any size)
  • Questions 40 MCQ
  • Time 80 minutes
  • Pass 60% (24/40)
  • Practical Separate pass required
  • Regulation EU 517/2014 (GB retained)
  • Blueprint May 2025 (v2.5)

Cycle Order RE

  • Compressor, condenser, expansion device, evaporator, repeat
  • Compressor: raises pressure Condenser: rejects heat Expansion: drops pressure Evaporator: absorbs heat

Superheat vs Sub-cooling RE

Superheat

  • Vapour above saturation temp
  • Protects compressor suction

Sub-cooling

  • Liquid below saturation temp
  • Prevents flash gas
  • Vapour side vs liquid side

Cycle Components RE

  • Compressor Raises P and T
  • Condenser Rejects heat, condenses
  • Expansion device Throttles, isenthalpic
  • Evaporator Absorbs heat, boils
  • Superheat Vapour above saturation temp
  • Sub-cooling Liquid below saturation temp
  • Flash gas Forms before expansion device

p-h Diagram Basics RE

  • Saturation dome Liquid and vapour coexist
  • Left of dome Sub-cooled liquid region
  • Right of dome Superheated vapour region
  • Throttling line Vertical, constant enthalpy
  • Evaporation line Horizontal, low pressure
  • Condensation line Horizontal, high pressure
  • Compression line Pressure, temperature both rise

Leak-Indication Components RE

  • Service valves Check points for leaks
  • Pressure relief valve Releases excess system pressure
  • Thermostats Control temp, flag faults
  • Sight glass bubbling Signals flash gas
  • Defrost controls Manage evaporator ice buildup
  • Overloads Protect compressor motor windings
  • Oil separator Returns oil, flags faults
  • High-pressure receiver Stores liquid, monitors charge
  • Low-pressure accumulator Prevents liquid floodback

CO2e Formula FG

  • CO2e = tonnes charge x GWP value
  • Mass in tonnes x GWP number = CO2 equivalent

517/2014 vs 842/2006 FG

517/2014 (current)

  • Retained EU law today
  • GB via SI 2015/310

842/2006 (superseded)

  • Predecessor regulation
  • Replaced in EU by 517/2014
  • Old rule replaced by new

Regulation & CO2e Triggers FG

  • Servicing with virgin HFC → Check GWP under 2500 ( Below 40t CO2e ban )
  • Any deliberate release → Always illegal, recover instead ( No exceptions )
  • Repair just completed → Follow-up check required ( Within 1 month )
  • Calculating CO2e → Multiply mass by GWP ( Tonnes x GWP factor )
  • Choosing low-GWP refrigerant → Check HFC phase-down quota ( Falling toward 2030 )

F-Gas Legal Framework FG

  • EU 517/2014 Retained EU law, GB
  • SI 2015/310 GB domestic implementation
  • Fluorinated GHG Regs 2015 Domestic UK statute
  • Deliberate venting Always illegal, any size
  • Category I Legally any charge size
  • Operator duty Arrange checks and records

Category I vs Category II-IV FG

Category I

  • Any charge size
  • Full scope: all activities

Category II-IV

  • Limited charge or scope
  • Narrower legal permissions
  • Broadest tier vs narrower tiers

CO2e & Service Rules FG

  • CO2e formula Mass(t) x GWP
  • 2020 HFC ban Virgin gas GWP 2500 plus
  • Ban threshold 40t CO2e charge size
  • Recycled/reclaimed HFC Still permitted after 2020
  • Phase-down target About one-fifth by 2030
  • Records kept At least 5 years
  • Record contents Type, quantity, dates, technician

Refrigerant Charging Method Picker SY

  • Zeotropic blend (e.g. R-404A) → Charge as liquid ( Prevents fractionation )
  • Azeotropic blend (e.g. R-507A) → Charge as liquid ( Behaves like pure fluid )
  • Sight glass bubbling → Check for undercharge ( Or restriction )
  • System evacuation needed → Pull deep vacuum ( About 500 microns )
  • Charging any refrigerant → Weigh on scales ( Charge by mass )

Core Hardware SY

  • TEV/TXV Modulates flow, targets superheat
  • Filter drier Removes moisture, acid, debris
  • Liquid receiver Stores surplus liquid charge
  • Manifold gauges Red high side, blue low
  • Vacuum pump Removes air and moisture
  • Vacuum level About 500 microns deep
  • Weighing scales Charge measured by mass
  • Zeotropic blend Charge as liquid only
  • Azeotropic blend Behaves like single substance

Leak Band Numbers LE

  • 5, 50, 500 tonnes set check frequency
  • 5t = 12-monthly 50t = 6-monthly 500t = 3-monthly + detector

Direct vs Indirect Leak Detection LE

Direct methods

  • Find the gas
  • Sniffer, UV dye, bubbles

Indirect methods

  • Infer from parameters
  • Pressure and temperature checks
  • Gas found vs signs read

Leak-Check Interval Picker LE

  • Charge 5 to <50t → Check every 12 months ( No fixed detector )
  • Charge 50 to <500t → Check every 6 months ( No fixed detector )
  • Charge 500t or more → Check every 3 months ( Fixed detector mandatory )
  • Fixed detector fitted → Double the interval ( Below 500t only )
  • Hermetic, labelled, under 10t → No routine check needed ( Exemption only )

Detection Methods LE

  • Electronic sniffer Direct detection method
  • UV dye and lamp Direct detection method
  • Bubble/soap solution Direct detection method
  • Indirect method Infers from operating parameters
  • Halide torch Unsuitable for modern HFCs
  • Detector sensitivity 5 grams per year
  • Detector calibration Checked every 12 months

Fixed Detector Present vs Absent LE

Fixed detector present

  • Doubles check interval
  • Mandatory above 500t

No fixed detector

  • Standard interval applies
  • 5t, 50t, 500t bands
  • Detector halves inspection frequency

Leak-Check Frequencies LE

  • 5 to under 50t 12-monthly checks required
  • 50 to under 500t 6-monthly checks required
  • 500t or more 3-monthly plus fixed detector
  • Fixed detector fitted Doubles the check interval
  • 5t band with detector Becomes 24-monthly checks
  • 50t band with detector Becomes 12-monthly checks
  • Hermetic exemption Below 10t, labelled only
  • Follow-up check Within 1 month of repair

Recycling vs Reclamation RE

Recycling

  • Basic filter and dry
  • Reused on-site often

Reclamation

  • Distilled to AHRI 700
  • Resold as new
  • Site clean-up vs full reprocessing

Recovery Cylinder Decision RE

  • Filling recovery cylinder → Stop at 80% full ( Leaves ullage space )
  • Refrigerant lightly contaminated → Recycle on site ( Filter and dry )
  • Refrigerant needs resale → Send for reclamation ( Must meet AHRI 700 )
  • Different refrigerant types → Use separate cylinders ( Avoid cross-contamination )
  • Refrigerant too contaminated → Send for destruction ( Licensed facility only )

Recovery Rules RE

  • Recovery Capture gas before disposal
  • Cylinder fill limit Max 80% liquid fill
  • Ullage space About 20% for expansion
  • Recycling Basic filter and dry
  • Reclamation Distilled, tested to AHRI 700
  • Cross-contamination Blocks recycling and reclaiming
  • Unusable refrigerant Sent for licensed destruction
  • Separate cylinders One refrigerant type each

GWP Memory Anchors EN

  • CO2 is 1, ammonia is 0
  • CO2 (R-744): GWP 1 Ammonia (R-717): GWP 0 R-1234yf: GWP under 1

CFC/HCFC vs HFC/HFO EN

CFC/HCFC

  • Contains chlorine
  • ODP greater than zero

HFC/HFO

  • No chlorine content
  • ODP equals zero
  • Chlorine present vs chlorine absent

GWP & ODP Values EN

  • GWP reference gas CO2 equals 1
  • R-410A GWP Approximately 2088
  • R-32 GWP Approximately 675
  • R-134a GWP Approximately 1430
  • R-404A GWP Approximately 3922
  • R-1234yf GWP Less than 1
  • Ammonia R-717 GWP Zero
  • ODP reference gas R-11 equals 1
  • CFC and HCFC ODP Greater than zero
  • HFC and HFO ODP Equals zero

Protocols & Treaties EN

  • Montreal Protocol Signed 1987, ozone treaty
  • Kigali Amendment Added 2016, HFC phase-down
  • Kyoto Protocol Climate change treaty basis
  • TEWI Total equivalent warming impact

Safety Hazards SA

  • Cold burns Liquid refrigerant skin contact
  • Asphyxiation Displaces oxygen when leaking
  • Thermal decomposition Refrigerant meets open flame
  • CNS effect Central nervous system depression
  • Cardiac sensitisation Heart arrhythmia risk, adrenaline
  • Flame brazing hazard Fire and fume risk
  • Nitrogen pressure testing Over-pressure and burst risk

Safety Rules & Equipment SA

  • HASAWA 1974 General workplace safety duty
  • COSHH Controls hazardous substance exposure
  • OFN Oxygen-free nitrogen for purging
  • Never use Oxygen or compressed air
  • PPE required Gloves and eye protection
  • Safe isolation Before opening any circuit

Common Traps

GWP vs ODP Confusion

  • GWP = warming, not ozone ≠ ODP = ozone, not warming

Superheat vs Sub-cooling Swap

  • Superheat = vapour side always ≠ Sub-cooling = liquid side always

5t Threshold Misread

  • 5t is CO2e, not kg ≠ Hermetic exempt only under 10t

Fixed Detector Confusion

  • Doubles interval below 500t ≠ Mandatory (not optional) at 500t

Recycling vs Reclamation Mixup

  • Recycling stays on-site basic ≠ Reclamation meets AHRI 700 spec

Venting Never Legal

  • No charge size exemption exists ≠ Always recover, never release

842/2006 vs 517/2014

  • 842/2006 is superseded now ≠ 517/2014 is current GB law

Last Minute

  • 1. 40 MCQ, 80 minutes, 60% pass
  • 2. Pass mark is 24 of 40
  • 3. Category I covers any charge size
  • 4. CO2e equals tonnes charge times GWP
  • 5. Leak bands: 5t, 50t, 500t
  • 6. Fixed detector doubles check interval
  • 7. Detector must sense 5 g/year
  • 8. Follow-up check due within 1 month
  • 9. Never vent; always recover refrigerant
  • 10. Recovery cylinders fill to 80% max
  • 11. Virgin HFCs GWP 2500+ banned 2020
  • 12. Keep F-Gas records for 5 years

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