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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
S
5 psig
65
5
F
242
145
75
5
F
281
145
85
5
F
325
148
95
5
F
377
149
105
5
F
415
150
115
5
F
472
151
TABLE 6 581066-01
036 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+10 psig
S 5
psig
65
5
F
259
144
75
5
F
301
147
85
5
F
347
149
95
5
F
390
152
105
5
F
448
155
115
5
F
511
157
TABLE 7 581067-01
048 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+10 psig
S 5
psig
65
5
F
247
129
75
5
F
284
134
85
5
F
328
137
95
5
F
375
140
105
5
F
425
143
115
5
F
480
144
TABLE 8 581068-01
060 NORMAL OPERATING PRESSURES
Outdoor Coil
Entering Air Temp
Discharge
+10 psig
S 5
psig
65
5
F
259
139
75
5
F
299
140
85
5
F
343
141
95
5
F
391
143
105
5
F
444
146
115
5
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)
