Refrigeration Cycle & p-h Diagrams
32%of exam
Compressor+condenserExpansion+evaporatorSuperheat vs sub-coolp-h diagram basicsLeak-indicator components
Refrigerants, F-Gas & ODS Regs
20%of exam
EU 517/2014 retained lawCO2e = mass x GWP2020 HFC service banHFC phase-down quota5-year record keeping
System Components
20%of exam
TEV/TXV + filter drierManifold gauges red/blueLiquid receiver + sight glassZeotropic vs azeotropic blendsDeep vacuum ~500 microns
Leak Detection & Repair
5%of exam
Direct vs indirect methods5g/year detector sensitivity12/6/3-month check bandsFixed detector doubles interval1-month follow-up check
Recovery, Recycling & Reclamation
5%of exam
80% cylinder fill limitRecycling vs reclamationAHRI 700 standardNo venting, everSeparate cylinders per gas
Environmental Impact (GWP/ODP)
5%of exam
GWP: CO2=1 referenceODP: R-11=1 referenceHFC high GWP, zero ODPMontreal 1987 ozone treatyKigali 2016 HFC phase-down
Safety & Legislation
13%of exam
HASAWA 1974 general dutyCOSHH hazardous substancesOFN for purge + testingCardiac sensitisation riskCold 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
Compressor, condenser, expansion device, evaporator, repeat
Compressor: raises pressureCondenser: rejects heatExpansion: drops pressureEvaporator: absorbs heat
Superheat vs Sub-cooling
Superheat
- Vapour above saturation temp
- Protects compressor suction
Sub-cooling
- Liquid below saturation temp
- Prevents flash gas
Vapour side vs liquid side
Cycle Components
- 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
- 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
- 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
CO2e = tonnes charge x GWP value
Mass in tonnesx GWP number= CO2 equivalent
517/2014 vs 842/2006
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
- 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
- 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
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
- 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
- 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
- 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
5, 50, 500 tonnes set check frequency
5t = 12-monthly50t = 6-monthly500t = 3-monthly + detector
Direct vs Indirect Leak Detection
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
- 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
- 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
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
- 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
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
- 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
- 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
CO2 is 1, ammonia is 0
CO2 (R-744): GWP 1Ammonia (R-717): GWP 0R-1234yf: GWP under 1
CFC/HCFC vs HFC/HFO
CFC/HCFC
- Contains chlorine
- ODP greater than zero
HFC/HFO
- No chlorine content
- ODP equals zero
Chlorine present vs chlorine absent
GWP & ODP Values
- 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
- 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
- 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
- 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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