Evacuation Procedures PDF

Evacuation RACM-145 Learning Outcomes Demonstrate the knowledge of the procedures used to evacuate refrigeration and air conditioning systems. Demonstrate basic knowledge of checking evacuation level. Why Evacuate? Refrigeration systems are designed to circulate refrigerant and oil...

Evacuation RACM-145 Learning Outcomes Demonstrate the knowledge of the procedures used to evacuate refrigeration and air conditioning systems. Demonstrate basic knowledge of checking evacuation level. Why Evacuate? Refrigeration systems are designed to circulate refrigerant and oil only. When gauges are installed, air enters. Air contains oxygen, nitrogen, and water vapor. These need to be removed. Removing moisture. POE, Mineral, and Alkylbenzene oils undergo hydrolysis when moisture is present (acid). Degassing – removing the noncondensables. Degassing Degassing is the removal of air/other gasses, like noncondensables. These take up space in the condenser coil, causing it to be undersized. Increased compression ratio. Higher operating temperatures. Decreased efficiency. Dehydration Dehydration is the removal of moisture. Moisture causes acid to form. Acid causes corrosion on windings. Copper pitting on steel parts, mainly the crankshaft. Copper pitting on crankshaft causes premature wearing and inefficient compression. Moisture + acid + oil = sludge. Theory of Evacuation The pump creates a low pressure point. The gases in the system flow high to low, so they travel to the pump, exiting the system. Lowering the pressure in the system, lowers the boiling point of the water vapor. Once the boiling point of the water vapor reaches the ambient temperature, it boils starts to evaporate. Water boils at 212 F at sea level, in Denver its 203 F, we need to lower the pressure to boil water at 20 F at times. Theory of Evacuation Vacuum is usually expressed in inches of mercury, or microns. There are 25,400 microns in 1 inch. 1000 microns = 1millimeter of mercury. On your compound gauge (low side) you will see it goes down to 29.92 in. mercury, which is 760,000 microns. You need a micron gauge to measure your vacuum, not the low side gauge. Theory of Evacuation Much easier to remove moisture in the vapor state. If liquid water is present in the system, it needs to boil off. 1 lb. of water @ 70 F will boil off into 867 cubic ft of water vapor. 1 lb. of water @ 32 F will boil off into 2837 cubic ft of water vapor. Water in Evacuation Micron Reading vs. Boiling Point Solenoid Service Tools Magnets designed to open solenoid valves. If the solenoid is normally closed, these must be used to allow flow. Can be used during recovery/pressure test as well. If you can pull on both sides of the system, it is not needed necessary. Microns Gauges Digital type gauge – High resolution. LED (light emitting diode) type is the most popular. Electronic analog type uses a separate sensor that attaches to the system and that is connected to the gauge with wires. These sensors must be mounted upright. Evacuation Hoses Higher flow. Lower leak rate under a vacuum. Typically, larger diameter hoses. Hose Diameter vs. Flow 12 CFM Vacuum Pump vs 2 CFM Vacuum Pump - YouTub e Compound Gauges Read positive pressure and negative pressure down to 29.92 inHg. Low side gauge. Ensure gauge is calibrated. Useful for a very quick decay test. Vacuum Pump Good pumps can pull down to 50 microns. Oil should be changed prior to using (not always practical). Creates the low pressure so gases flow from system (high pressure) to the pump (low). Uses rotary compressors. Uses high refined mineral oil, that has LOW vapor pressure. Usually 2 stages, the gas ballast is opened until roughly 2000 microns, and closed until the desired vacuum is achieved. Core Removal Tools Schraders are very restrictive. Remove/replace schrader cores on live systems. Remove cores to allow for maximum flow when recovering or pulling evacuation. Safe way to install/remove gauges to prevent refrigerant burns. Can come in ¼” or 5/16” for 410a. Fieldpiece/Appion are the best. How and When to Use a Schrader Core Removal Tool Vacuum Manifolds Engineered for evacuations. High flow, flutter less gauge and isolation valves. Attachment for micron gauge. Isolation valves for decay test. Vacuum rated. Cold Trap Refrigerated volume in the vacuum line between the evacuation line and wet system. When the water vapor passes through the trap, it freezes to the sides of the trap. The trap is heated, and pressurized every so often to drain the trap thus, removing moisture. Usually refrigerated with dry ice. Cold Trap Set Up Microns and Measurement Micron gauge should be installed at the furthest spot from the pump. Ex. Liquid line if pulling on the suction line. Initial pulldown to 250 – 500 microns. The pump should be turned off, and valved off from the system. Allow reading to settle, wait 10-30 minutes. The reading should hold 250-500 microns, or manufacturers start up specifications. Decay Test Leak Notice the sharp increase in pressure. High decay rate. This will eventually go to atmospheric pressure. Decay Test Moisture Notice the low decay rate. The reading is tailing off, meaning not rising anymore. System needs additional time under evacuation. Trapped Moisture Moisture can get trapped in bottom parts of the evaporator coils, condenser coils, receivers, and compressor oil. Heat can be applied to turn the water to vapor, allowing the pump to remove it. This can save a fair bit of time on wet/larger systems. If moisture is trapped in the compressor crankcase, it cannot escape due to the valves. Why? Pressurizing a with a slight positive pressure, the compressor can be started for a few seconds to open/flush the valves. Applying Heat to Crankcase Triple Evacuation Used on contaminated/wet systems. Step 1 – Evacuate to roughly 1500 microns. Step 2 – Break vacuum (increase to near positive pressure) with nitrogen, sweeping the system. Step 3 – Evacuate to roughly 1500 microns. Step 4 – Evacuate to 250-500 microns. Step 5 – Valve off pump, complete the 10-15 minute decay test. Evacuation without Manifold