37
2. Using hoses with valve core depressors, attach low- and
high-pressure gage hoses to low- and high-pressure ser-
vice fittings, respectively.
3. Start unit in Cooling Mode and let unit run until system
pressures stabilize.
4. Measure and record the following:
a. Outdoor ambient-air temperature (F db).
b. Evaporator inlet-air temperature (F wb).
c. Suction-tube temperature (F) at low-side service
fitting.
d. Suction (low-side) pressure (psig).
5. Using “Cooling Charging Charts” compare outdoor-air
temperature (F db) with the suction line pressure (psig) to
determine desired system operating suction line tempera-
ture. See Fig. 50-53.
6. Compare actual suction-tube temperature with desired
suction-tube temperature. Using a tolerance of ± 3
°
F, add
refrigerant if actual temperature is more than 3
°
F higher
than proper suction-tube temperature, or remove refriger-
ant if actual temperature is more than 3
°
F lower than re-
quired suction-tube temperature.
TO USE COOLING CHARGING CHARTS — This meth-
od is to be used in Cooling mode only. Take the outdoor ambi-
ent temperature and read the suction pressure gage. Refer to ap-
propriate chart to determine what suction temperature should
be. If suction temperature is high, add refrigerant. If suction
temperature is low, carefully recover some of the charge. Re-
check the suction pressure as charge is adjusted.
EXAMPLE: (Fig. 53; Circuit 1)
Outdoor Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85 F
Suction Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 psig
Suction Temperature should be. . . . . . . . . . . . . . . . . . . . . . .54 F
(Suction Temperature may vary ± 3° F.)
High-Pressure Switch —
Located on the compressor
hot gas line is a high-pressure switch containing a Schrader
core depressor. This switch opens at 428 psig and closes at
320 psig. No adjustment is necessary. Refer to Table 1.
Loss-of-Charge Switch —
Located on the condenser
liquid line is a low-pressure switch which functions as a loss-
of-charge switch. This switch contains a Schrader core depres-
sor. This switch opens at 7 psig and closes at 22 psig. No
adjustment is necessary. Refer to Table 1.
Freezestat —
Located on the “hair pin” end of the evapo-
rator coil is a bimetal temperature sensing switch. This switch
protects the evaporator coil from freeze-up due to lack of
airflow. The switch opens at 30 F and closes at 45 F. No adjust-
ment is necessary. Refer to Table 1.
Fig. 50 — Cooling Charging Chart; 50TFF008
CIRCUIT NO. 1
CIRCUIT NO. 2
Fig. 51 — Cooling Charging Chart; 50TFF009
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