Mollier Diagram

Whether you're a seasoned technician or a student just starting out, the Mollier Diagram (P-H Diagram) is one of the most powerful tools in a refrigeration professional's diagnostic arsenal. But let’s be honest—at first glance, the chart looks like a chaotic mess of overlapping lines. In this video, Resource Compliance breaks down the P-H diagram into clear, actionable steps. We move past the theory and show you how to use this "map" to visualize what is happening to the refrigerant as it moves through the compressor, condenser, expansion valve, and evaporator. What You’ll Learn: 1) The Anatomy of the Curve: Understanding the "saturated liquid" and "saturated vapor" lines (the "curve"). 2) Plotting the 4 Stages: How to map the standard refrigeration cycle (Compression, Condensation, Expansion, Evaporation) directly onto the chart. 3) The Math Made Easy: Using the diagram to calculate refrigeration effect, heat of compression, and more. 4) Real-World Analysis: How to identify common circumstances—like increased condensing pressure, superheat at the compressor inlet, and subcooling at the condenser outlet. Timestamps: 0:00 – Introduction: What is a Mollier Diagram? 1:21 – Explaining the diagram 2:38 – Defining the Saturated State (The "Dome"). 3:41 – Explaining what each line measures 6:59 – Plotting a Live System: Step-by-Step. 11:49 – Calculating "non-refrigeration effect" and "refrigeration effect" 12:48 – Calculating heat gain in suction piping 13:16 – Calculating "heat of compression" 14:15 – Analysis: Increasing condensing pressure/temperature 15:05 – Analysis: Decreasing evaporator pressure/temperature 16:02 – Analysis: Superheat at compressor inlet 16:28 – Analysis: Subcooling at condenser outlet 16:59 – Analysis: Decreasing the condensing pressure/temperature 17:48 – Analysis: Two-stage system 20:38 – Conclusion