Mercedes AC System Explained: Key Components for W123, W124, W126, W201 R107

This video is about Key components of AC systems on Mercedes Benz W123 W124 W126 W201. Some good info to know about how the system works. For anyone who would like to troubleshoot such systems. A good source of information for anyone who wants to convert from R12 to R134a freon. Note: The red high/ low speed fan speed switch on the dryer is actually the S32 high pressure AC switch, which is open at 12Bar and closes at 16Bar on US spec W126 (green switch 15/20Bar). The coolant temp switch S25 105C/115C is located on the engine and will eventually switch off the compressor. In this technical overview, Ralf from Stray Benzes provides a detailed explanation of the air conditioning (AC) systems found in classic Mercedes-Benz models like the W123, W124, W126, and W201. He breaks down the fundamental principles of how these systems work, identifies each major component under the hood, and explains their specific roles in keeping the cabin cool. Video Chapters [00:01] Introduction: Overview of AC systems across classic Mercedes-Benz chassis. [00:53] Basic Principles: Comparing automotive AC to a household refrigerator. [01:14] The Refrigerant Cycle: Compression, liquefaction, and expansion. [02:57] The Compressor: The role of the electric clutch and high-pressure lines. [03:39] The Condenser: Why airflow and the auxiliary (AUX) fan are critical. [04:17] Ports and Switches: High-pressure measuring ports and safety cutouts. [05:48] Receiver Drier: Filtering moisture and protecting the expansion valve. [06:15] Interior Components: The expansion valve and hidden evaporator unit. [06:42] Fuel Cooling: A unique feature on gas-engine Mercedes models. [07:41] R134a Conversion: Identifying modified low-pressure ports for modern gauges. Video Summary The air conditioning system in a classic Mercedes operates on the same basic principles as a home refrigerator, using a refrigerant (like Freon) that is continuously compressed and expanded in a closed loop. Ralf methodically traces this loop, starting from the compressor and following the refrigerant as it moves through the engine bay and into the cabin. Key Technical Highlights: The Compressor: This component is the heart of the system, using an electric clutch that engages when the climate controller calls for cooling. It compresses the refrigerant gas, which generates heat as it transitions toward a liquid state. The Condenser: Located in front of the actual radiator, the condenser dissipates heat from the compressed gas to liquefy it. The auxiliary (AUX) fan is essential here, as it provides the necessary airflow to ensure the condenser can effectively cool the refrigerant. Safety Switches: The system includes a pressure-sensing switch that prevents the compressor from engaging if the refrigerant pressure is too low. Additionally, a high-temperature cutout will disengage the compressor if the engine begins to overheat, prioritizing power for the engine itself. Receiver Drier: This canister contains a drying agent designed to remove any trace amounts of moisture from the refrigerant, protecting internal components from corrosion and freezing. Expansion Valve & Evaporator: The liquid refrigerant flows into the expansion valve, where it is allowed to expand back into a gas within the evaporator core inside the cabin. This expansion causes a rapid drop in temperature, which the cabin fan then blows across to cool the interior. Fuel Cooler Feature: On gasoline-powered models, the returning cool AC gas is used to cool the fuel just before it enters the fuel injection system. This reduces the risk of vapor lock during hot summer months. Modern Conversion: Ralf notes that systems converted to R134a will have specialized hardware on the low-pressure and high-pressure ports to accommodate modern manifold gauges. Video URL:    • Mercedes AC System Explained: Key Componen...