37 °C saturation − 31 °C liquid = 6 K subcooling at the condenser outlet.
Swipe either way · Tap to enlarge · A sample of the book, not the full PDF.
THE DRAWN METHOD
The numbers are not the hard part. Knowing what the refrigerant is doing is.
The readings change depending on where you measure. Choose a checkpoint and see what the drawing clears up.
✕Without the drawing
You read a low-side gauge but cannot explain whether the refrigerant is liquid, vapour or both.
✓With the drawn page · Page 8
The page draws the evaporator with heat entering: refrigerant absorbs heat and changes state, labelled at each point.
✕Without the drawing
You switch between bar(g) and bar(a) without noticing which reference the table uses.
✓With the drawn page · Page 24
Gauge starts at atmosphere, absolute starts at vacuum: both scales side by side with the offset drawn.
✕Without the drawing
You calculate subcooling but get a negative number and do not know what went wrong.
✓With the drawn page · Page 40
Bubble-point temperature minus measured liquid temperature: the drawing walks through one reading with the correct reference.
✕Without the drawing
In heating mode you cannot tell which coil is the condenser and which is the evaporator.
✓With the drawn page · Page 47
The reversing valve swaps coil connections: both modes drawn side by side with discharge and suction labelled.
✕Without the drawing
You know the GWP but cannot explain what two kilograms of that refrigerant means in tonnes CO₂e.
✓With the drawn page · Page 54
Mass times GWP divided by one thousand: each figure placed on the drawing beside the formula.
1 / 5
Five of the 64 drawn pages: every part of the circuit has its own.
THE SAME TOPIC · TWO WAYS TO STUDY
The same topic, two ways to study it.
Dense text
Subcooling: a continuous paragraph
×Parse a dense paragraph for the right subtraction
×Remember which temperature is bubble-point
×Spot the pressure-reference mix-up buried in the text
Subcooling is defined as the difference between the saturation temperature at the bubble point corresponding to the measured condensing pressure and the temperature of the liquid refrigerant measured at the condenser outlet, expressed in kelvin, and must be calculated using the correct pressure reference, whether gauge or absolute, in conjunction with the appropriate saturation data for the specific refrigerant blend or pure substance in use, taking into account that a negative result indicates the measurement or reference was applied incorrectly rather than the presence of superheat at the liquid line.
Drawn on the page
See subcooling on one drawn page
See bubble-point and measured temperature on the same drawing
Follow the subtraction with both values labelled
Check your answer against a worked reading
MADE FOR YOUR STARTING POINT
Where do you start?
01
Revising for an F-gas assessment
You study after shifts and the readings blur together. You want each topic on one clear page to check on the bus or in the break room.
02
Moving from boilers to heat pumps
Refrigerant circuits are new territory. You need the reversing valve and both modes drawn, not described in dense paragraphs.
03
Reading gauges on site every day
You know the numbers but want to explain them clearly. A drawn circuit for superheat, subcooling and pressure lets you point to what you mean.
A CLEAR PATH
See what is inside.
Open a part to see the topics covered.
The four checkpoints are a study method in this book, not an industry standard or professional certification. For assessment preparation, match revision to your own qualification specification.
01Find Your Way RoundPage 5–11
Four Checkpoints, One Circuit
Follow the Arrows
Liquid, Vapour or Both
Heat Moves Across a Temperature Difference
Temperature Is Not Heat
Boiling Does Not Mean Hot
02What Each Checkpoint DoesPage 12–19
The Compressor Raises Vapour Pressure
Discharge Vapour Can Be Above Saturation
The Condenser Rejects Heat
Condensation Occupies Part of the Coil
The Expansion Device Drops Pressure
The Evaporator Absorbs Heat
Suction Vapour Returns to the Compressor
Oil Travels With the Refrigerant
03Read Pressure with ContextPage 20–27
High Side and Low Side
Gauge Pressure Starts at Local Atmosphere
Absolute Pressure Starts at Vacuum
A Negative Gauge Reading Is Not Negative Pressure
Check the Unit Before the Number
Compound Gauges Cross Zero
Digital Gauges Need the Same Check
Convert Only When the Reference Matches
04Connect Pressure and TemperaturePage 28–35
Saturation Temperature Comes from a Reference
Superheat Is a Temperature Difference
Work Through One Superheat Reading
Subcooling Is a Temperature Difference
Work Through One Subcooling Reading
Approach Temperature Is Not Superheat
Glide Matters for Zeotropic Blends
Use Midpoint for Display Accuracy
05Choose the Right Refrigerant DataPage 36–43
Start with the Equipment Label
R32 Uses Its Own Saturation Curve
R410A Is a Blend
Use Dew Temperature for Vapour Superheat
Use Bubble Temperature for Liquid Subcooling
R290 Is Flammable: A2L and A3 Differ
Saturation Tables Vary by Source
Record the Refrigerant and the Reference
06Trace a Reversible Heat PumpPage 44–50
Name the Coil by Its Current Job
Cooling Mode: Heat Leaves the Building
Heating Mode: Heat Enters the Building
The Reversing Valve Redirects Flow
Defrost Returns to Cooling Briefly
Check Superheat and Subcooling in Each Mode
Water-Side and Air-Side Differ
07Keep GB Rules in ViewPage 51–56
Great Britain Has a Defined Scope
A Study Book Does Not Authorise Refrigerant Work
Match Revision to Your Assessment
Kilograms and Tonnes CO₂e Measure Different Things
Certificate Categories Set the Boundaries
Leak Checks Follow a Schedule
08Practise the Same OrderPage 57–64
Rebuild the Four-Checkpoint Circuit
Explain a Reading in Four Steps
Catch the Pressure-Reference Mix-Up
Complete a Superheat Example
Complete a Subcooling Example
Identify the Coil Job in a Heat Pump
Match the Rule to the Category
Review With the Worked Answers
IMAGINE YOUR NEXT REVISION SESSION
Open the page and the reading makes sense.
Here is how revision goes with the guide in front of you.
You see a gauge and know which checkpoint to look at.
Superheat and subcooling belong to a drawn circuit, not a formula sheet.
You explain a reading to someone else without second-guessing the reference.
The assessment question matches a page you already traced.
A guide and its companion books, together in one digital pack.
THE CORE GUIDE
Refrigeration: Trace the Circuit
Follow the refrigerant through four drawn checkpoints: compressor, condenser, expansion device and evaporator. Each page covers one topic with the circuit drawn, from pressure scales to heat pump modes.
Included
FREE BONUS 01
Gauge Reading Practice: 40 Worked Cases
Turn supplied readings into an explanation of the circuit: superheat, subcooling, pressure side and refrigerant state, with worked answers to check your own.
£15.99 · FREE
FREE BONUS 02
F-Gas Recall Cards: GB Rules and Mix-Ups
Keep certificate categories, CO₂-equivalent figures and record-keeping distinctions together instead of revising them as disconnected facts.
Offers change, and we can’t guarantee the same price tomorrow.
30-day money-back guarantee
Digital books. No physical books are shipped.
Reviews
Reader experiences
Selected experiences supplied for this product.
TOP 01LR
Liam R.
Following the refrigerant through the four drawn checkpoints completely changed how I read my manifold gauges. Connecting pressure to temperature on a real circuit makes superheat calculations second nature.
TOP 02JH
James H.
Passed my F-Gas Category 1 assessment with confidence! The reversible heat pump diagrams and 4-way valve troubleshooting guide are the clearest visual explanations I’ve ever seen.
TOP 03CS
Callum S.
Trainees often struggle because gauge numbers mean different things depending on where you probe. This book pins down each checkpoint visually, removing all the guesswork on site.
TOP 04DW
Daniel W.
Brilliant coverage of GB regulations and practical fault-finding on modern refrigerants. Keep this on your phone or tablet in the van—it saves hours of diagnosing phantom issues.
TOP 05OB
Oliver B.
Straightforward, highly technical, yet incredibly easy to digest. A must-have field and revision companion for every refrigeration and air conditioning apprentice in the UK.
MONEY BACK30DAYS
Take 30 days to try it.
Trace the circuit through the drawings. If following the four checkpoints does not clear up the readings for you, tell me what did not work and I will refund you in full.
It is a digital book in PDF, delivered by email. The two included books are also in PDF. You can print any of them.
Can I read it on my phone?
Yes. You can read the pages on your phone, tablet or computer.
Does it cover heat pumps?
Yes. Part VI traces the refrigerant through a reversible heat pump in both heating and cooling modes, including the reversing valve and defrost.
How do I receive the material?
The book and the two included books arrive in PDF by email to the address you give at checkout.
Is it a one-off payment?
Yes. The payment for the pack is one-off and does not include a subscription.
Is it written for Great Britain?
Yes. Part VII covers GB-retained F-gas rules, certificate categories and CO₂-equivalent thresholds. Northern Ireland requires separate guidance.
Will this qualify me for F-gas work?
No. This is study material. It does not replace training, assessment or certification by an awarding organisation. Match revision to your own qualification specification.
Can I print it?
Yes. The PDF is ready to print so you can keep the pages beside you while you study.
Does it replace manufacturer instructions?
No. Worked readings are examples for study. For any specific machine, follow the manufacturer’s documentation and your employer’s procedures.
What if the drawings do not help me?
You have a 30-day guarantee. If tracing the circuit through the drawings does not clear up the readings for you, tell me what did not work and I will refund you in full.
YOUR NEXT STEP
Your next revision session has a circuit to follow.
Get the full digital pack and trace the refrigerant at your own pace. Every reading has a checkpoint. Every checkpoint has a drawing.
