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Recovery equipment rated for R410a must be used. Recovery cylinders must have a service pressure rating of 400 psig (DOT 4BA 400 and DOT 4BW 400 are acceptable). DO NOT USE STANDARD DOT RECOVERY OR STORAGE CYLINDERS WITH A 300 PSIG RATING WITH R410A! As stated earlier, a specifi c gauge set for use with R410a is required. These will allow pressure measurements to 800 psig on the high side and 250 psig on the low side. Hoses should have a service rating of 800 psig. Evacuation Heat Controller recommends two evacuation methods, the deep vacuum method and the “Triple Vac” method. The Deep Vacuum Method The deep vacuum method requires a vacuum pump capable of at least a 500 micron vacuum and a micron gauge capable of measuring this vacuum. The deep vacuum method is the most positive way of assuring a system is free of air and moisture and is the recommended method. Triple Vacuum Method The triple evacuation method should only be used when the vacuum pump is not capable of pulling a 500 micron vacuum. See Figure 2. Figure 2. Triple Vacuum Procedure Figure 3. Vacuum and Time The following is the Triple Evacuation procedure: 1. The unit should be evacuated to at least 29.72 in. Hg. 2. Break the vacuum with dry nitrogen and wait 1 hour. 3. Evacuate until at least 29.72 in. Hg. is reached and then continue for 15 minutes. 4. Break the vacuum with dry nitrogen and wait 1 hour. 5. Evacuate until at least 29.72 in. Hg. is reached and then continue for 20 minutes. 6. Isolate and Turn Vacuum Pump Off and wait. Vacuum measurement should stay low and not rise above 29.5 in. Hg. A rise above 29.5 in. Hg indicates a leak or moisture in system. Refrigerant Charging An undercharged TXV unit can be identifi ed by: • Low evaporating pressure • High superheat • Low subcooling Page 6 R410a Application and Service Guide An overcharged TXV unit can be identifi ed by: • High subcooling • High head pressures Even though R410a has a very small fractionation potential it cannot be ignored completely when charging. To avoid fractionation, charging a system with R410a should be done with LIQUID from the tank to maintain optimum system performance. To ensure the proper blend of refrigerant is used, it is important that liquid only be removed from the storage tank. Some cylinders use dip tubes which allow liquid to be extracted from the cylinder. These can be identifi ed as recovery tanks with yellow tops and gray bottom and have a dual liquid and vapor valve assembly. Storage tanks without dip tubes will need to be tipped upside down in order for liquid to be removed. Once the liquid is removed from the storage cylinder, it can be charged into the system in the vapor state as long as all of the refrigerant is used from the charging cylinder. Liquid charging can be accomplished by using: • A throttling valve (Figure 3) to ensure the liquid vaporizes as it enters the suction line of the unit. • .he gauge set valve as a throttling device to restrict liquid from fl ooding the compressor during charging. Recharging should always be accomplished by using the nameplate charge. When this is not possible, charging using the subcooling method can be done using the following procedure. This method requires accurate gauges and a digital strap-on temperature meter. 1. Operate system for 10 minutes to stabilize. 2. Ensure that the unit has proper water and air fl ow and the air fi lter is clean. 3. Attach gauges to discharge port and record the saturation temperature at this pressure using a pressure/temperature chart for R410a. 4. Measure the liquid line (LL) temperature (between aircoil and TXV in heating and between coax and TXV in cooling). 5. Subtract the LL temperature from the saturation pressure to fi nd the subcooling. Consult Table 4 for appropriate values. 6. If the subcooling is too low add 2-4 oz.; if too high, remove 2-4 oz. Typical values are shown in Table 4. Superheat can be calculated similarly. This method also requires accurate gauges and digital strap-on thermometer. 1. Operate system for 10 minutes to stabilize. 2. Ensure that the unit has proper water and air fl ow and the air fi lter is clean. 3. Attach gauges to suction port and record the saturation temperature at this pressure using a pressure/ temperature chart for R410a. Figure 3. Throttling Valves Table 4. Typical Pressure and Temperatures (HTV060 Shown) HTV060 Full Load Cooling - without HWG active Full Load Heating - without HWG active Entering Water T emp.F Water Flow GPM Suction Pressure PSIG Discharge Pressure PSIG Super-heat Subcooling Water Temp Rise .F Air Temp Drop.F DB Suction Pressure PSIG Discharge Pressure PSIG Super-heat Subcooling Water Temp Drop .F Air Temp Rise.F DB 7.5 117-127 170-190 27-32 15-20 18.2-20.2 17-23 66-76 282-302 10-16 9-14 8-10 19-25 30 11.3 116-126 143-163 28-33 13-18 12.6-14.6 17-23 69-79 285-305 10-16 9-14 6-8 19-25 15.0 115-125 135-155 29-34 12-17 7-9 17-23 72-82 289-309 10-16 10-15 4-6 20-26 7.5 128-138 238-258 16-21 14-19 20.5-22.5 21-2...