Lennox LHT/LDT024 Installation Instructions Manual page 25

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.
S Add or remove charge in increments.
S 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
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.
LHT/LDT024, 036, 048, 060
 
F + 1 (2.1 C +
Unit
024
036
048
060
Page 25
TABLE 5 581065-01
024 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
655 F
755 F
855 F
955 F
1055 F
1155 F
TABLE 6 581066-01
036 NORMAL OPERATING PRESSURES
Outdoor Coil Discharge
Entering Air Temp
655 F
755 F
855 F
955 F
1055 F
1155 F
TABLE 7 581067-01
048 NORMAL OPERATING PRESSURES
Outdoor Coil Discharge
Entering Air Temp
655 F
755 F
855 F
955 F
1055 F
1155 F
TABLE 8 581068-01
060 NORMAL OPERATING PRESSURES
Outdoor Coil Discharge
Entering Air Temp
655 F
755 F
855 F
955 F
1055 F
1155 F
TABLE 9
SUBCOOLING TEMPERATURE
Liquid Saturated Temp. Minus
Liquid Temperature
7.4°F + 1 (4.1°C + 0.5)
7.6°F + 1 (4.2°C + 0.5)
5.7°F + 1 (3.2°C + 0.5)
6.8°F + 1 (3.8°C + 0.5)
Discharge Suction +
+10 psig 5 psig
242 145
281 145
325 148
377 149
415 150
472 151
Suction + 5
+10 psig psig
259 144
301 147
347 149
390 152
448 155
511 157
Suction + 5
+10 psig psig
247 129
284 134
328 137
375 140
425 143
480 144
Suction + 5
+10 psig psig
259 139
299 140
343 141
391 143
444 146
506 148