Refrigeration Installation
Turn service valves full out CCW (see Table 5) and then turn back in one-half turn to open service ports. Add the required refrigerant so that the total charge calculated for the unit and line set is now in the system. Open the service valve fully counter clockwise so that the stem will backseat and prevent leakage through the schrader port while it is not in use. Start unit in the heating mode and measure superheat and subcooling values after 5 minutes of run time. See tables 14a to 15 for superheat and sub-cooling values. Superheat is measured using suction temperature and pressure at the compressor suction line. Subcooling should be measured using the liquid line temperature immediately outside the compressor section cabinet and either the liquid line service valve pressure or the compressor discharge pressure. Note that different values from tables 14a to 15 will be obtained due to the pressure losses through the condenser heat exchanger. Adding refrigerant will increase sub-cooling while superheat should remain fairly constant allowing for a slight amount of hunting in TXV systems. This increase in subcooling will require 5 minutes or so of operation before it should be measured. After values are measured, compare to the chart and go to “FINAL EVALUATION.”
PARTIAL CHARGE METHOD - Open service valve fully counterclockwise and then turn back in one-half turn to open service port. Add vaporized (Gas) into the suction side of the compressor until the pressure in the system reaches approximately 60-70 psig (R-22 systems) or 100-120 psig (R-410A systems). Never add liquid refrigerant into the suction side of a compressor. Start the unit in heating and add gas to the suction port at a rate not to exceed five pounds [2.27 kg] per minute. Keep adding refrigerant until the complete charge has been entered. Superheat is measured using suction temperature and pressure at the compressor suction line. Subcooling should be measured using the liquid line temperature immediately outside the compressor section cabinet and either the liquid line service valve pressure or the compressor discharge pressure. Note that different values from tables 14a to 15 will be obtained due to the pressure losses through the condenser heat exchanger. Adding refrigerant will increase sub-cooling while superheat should remain fairly constant allowing for a slight amount of hunting in TXV systems. This increase in subcooling will require 5 minutes or so of operation before it should be measured. After values are measured, compare to the chart and go to
“FINAL EVALUATION.”
FINAL EVALUATION -In a split system, cooling subcooling values can be misleading depending on the location of the measurement. Therefore, it is recommended that charging be monitored in the heating mode. Charge should be evaluated by monitoring the subcooling in the heating mode. After initial check of heating sub-cooling, shut off unit and allow to sit 3-5 minutes until pressures equalize. Restart unit in the cooling mode and check the cooling superheat against Tables 14a to 15. If unit runs satisfactorily, charging is complete. If unit
R e s i d e n t i a l S p l i t - 6 0 H z R 2 2 & R 4 1 0 A
R e v. : 5 J u n e , 2 0 0 8
does not perform to specifications the cooling TXV (air coil side) may need to be readjusted (if possible) until the cooling superheat values are met.
Checking Superheat and Subcooling
Determining Superheat:
1.Measure the temperature of the suction line at a point near the expansion valve bulb.
2.Determine the suction pressure by attaching refrigeration gauges to the suction schrader connection at the compressor.
3.Convert the pressure obtained in step 2 to saturation temperature (boiling point) by using the pressure/ temperature conversion table on the gauge set.
4.Subtract the temperature obtained in step 3 from step
1. The difference will be the superheat of the unit or the total number of degrees above saturation temperature. Refer to Tables 14a to 15 for superheat ranges at specific entering water conditions.
Example (R-22 refrigerant):
The temperature of the suction line at the sensing bulb is 50°F. The suction pressure at the compressor is 65 psig which is equivalent to 38°F saturation temperature from the R-22 press/temp conversion table on the gauge set.
38°F subtracted from 50°F = 12°F Superheat.
Determining Sub-Cooling:
1.Measure the temperature of the liquid line on the smaller refrigerant line (liquid line) just outside of the cabinet. This location will be adequate for measurement in both modes unless a significant temperature drop in the liquid line is anticipated.
2.Determine the condensor pressure (high side) by attaching refrigerant gauges to the schrader connection on the liquid line service valve. If the hot gas discharge line of the compressor is used, refer to the appropriate column in Tables 14a to 15.
3.Convert the pressure obtained in step 2 to the saturation temperature by using the press/temp conversion table on the gauge set.
4.Subtract the temperature of Step 3 from the temperature of Step 1. The difference will be the sub-cooling value for that unit (total degrees below the saturation temperature). Refer to Tables 14a or 6b for sub-cooling values at specific entering water temperatures.
Example (R-22 refrigerant):
The condenser pressure at the service port is 225 psig, which is equivalent to 110°F saturation temperature. Discharge pressure is 236 psig at the compressor (113°F saturation temperature). Measured liquid line temperature is 100°F. 100°F subtracted from 110°F = 10 degrees sub- cooling (13 degrees if using the compressor discharge pressure).
