Charging the indoor TXV in subcooling mode
About this task:
The outdoor unit comes equipped with subcooling charts optimized for that particular unit. Follow
the instructions on the unit. If those instructions are not readily available, follow the instructions
below.
1. Set the system running in cooling mode by setting the thermostat at least 6°F below the
room temperature and operate the system for at least 10 min to 15 min.
2. Refer to the Technical Guide for the indoor airflow and verify it is correct (it must be between
350 SCFM/ton and 400 SCFM/ton).
3. Measure and record the indoor wet bulb (WB) and the outdoor ambient dry bulb (DB)
temperature.
4. Using the charging chart located on the unit, find the intersection of the indoor wet bulb and
the outdoor dry bulb. This is the recommended liquid pressure (and subcooling value).
5. Measure and record the pressure at the liquid valve pressure port and compare to the value
obtained in Step 4.
6. Add charge if the measured liquid pressure is lower than the recommended value. Remove or
recover charge if the measured liquid pressure is above the recommended value.
Example:
The liquid pressure listed at the intersection of the indoor WB and the outdoor DB is 320 psig.
The pressure at the liquid valve is 305 psig. It is necessary to add refrigerant to increase the
liquid pressure to 320 psig.
Note:
Condenser subcooling is obtained by calculating the difference between the saturated
refrigerant temperature of the pressure measured at the liquid base valve and the liquid
tube temperature as measured at the liquid base valve.
Subcooling Temperature (TC) = Saturated Temperature (TS) – Liquid Temperature (T)
CAUTION
It is unlawful to knowingly vent, release, or discharge refrigerant into the open air during repair,
service, maintenance, or the final disposal of this unit.
R-454B saturation properties
Table 10: R-454B saturation properties
Temperature Liquid pressure Vapor pressure
°F psig psig
35 101 97
40 112 107
45 123 118
50 135 129
55 148 142
60 161 155
65 175 168
70 191 183
75 206 199
80 223 215
85 241 233
90 260 251
95 280 270
Installation Manual: R-454B Outdoor Split-System Air Conditioner42
Johnson Controls Ducted Systems
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