Lennox LHT/LDT024

Page 25
LHT/LDT024, 036, 048, 060
2- Use a thermometer to accurately measure the
outdoor ambient temperature.
3- Apply the outdoor temperature to tables 5 through 8
to determine normal operating pressures. Pressures
are listed for sea level applications at 80°F dry bulb
and 67°F wet bulb return air.
4- Compare the normal operating pressures to the
pressures obtained from the gauges. Minor variations in
these pressures may be expected due to differences in
installations. Significant differences could mean that the
system is not properly charged or that a problem exists
with some component in the system. Correct any
system problems before proceeding.
5- If discharge pressure is high, remove refrigerant from
the system. If discharge pressure is low, add
refrigerant to the system.
 Add or remove charge in increments.
 Allow the system to stabilize each time
refrigerant is added or removed.
6- Use one of the following charge verification methods
along with the normal operating pressures to confirm
readings.
Charge Verification - Approach Method - AHRI Testing
1- Using the same thermometer, compare liquid
temperature to outdoor ambient temperature.
Approach Temperature = Liquid temperature (at
condenser outlet) minus ambient temperature.
2- Approach temperature should be 3.8F + 1 (2.1C +
0.5). An approach temperature greater than this
value indicates an under-charge. An approach
temperature less than this value indicates an
overcharge.
3- The approach method is not valid for grossly over or
undercharged systems. Use table 1 as a guide for
typical operating pressures.
TABLE 5 581065-01
024 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+
10 psig
Suction +
5 psig
655 F 242 145
755 F 281 145
855 F 325 148
955 F 377 149
1055 F 415 150
1155 F 472 151
TABLE 6 581066-01
036 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+
10 psig
Suction + 5
psig
655 F 259 144
755 F 301 147
855 F 347 149
955 F 390 152
1055 F 448 155
1155 F 511 157
TABLE 7 581067-01
048 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+
10 psig
Suction + 5
psig
655 F 247 129
755 F 284 134
855 F 328 137
955 F 375 140
1055 F 425 143
1155 F 480 144
TABLE 8 581068-01
060 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+
10 psig
Suction + 5
psig
655 F 259 139
755 F 299 140
855 F 343 141
955 F 391 143
1055 F 444 146
1155 F 506 148
TABLE 9
SUBCOOLING TEMPERATURE
Unit
Liquid Saturated Temp. Minus
Liquid Temperature
024 7.4°F + 1 (4.1°C + 0.5)
036 7.6°F + 1 (4.2°C + 0.5)
048 5.7°F + 1 (3.2°C + 0.5)
060 6.8°F + 1 (3.8°C + 0.5)