Carrier 69NT40-541-306, Операция и обслуживание

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7–21 T-354
7.13 FILTER-DRIER
On units equipped with a water-cooled condenser, if the sight glass appears to be flashing or bubbles are con-
stantly moving through the sight glass when the suction modulation valve is fully open, the unit may have a low
refrigerant charge or the filter-drier could be partially plugged.
To Check Filter-Drier:
1. Test for a restricted or plugged filter-drier by feeling the liquid line inlet and outlet connections of the drier
cartridge. If the outlet side feels cooler than the inlet side, then the filter-drier should be changed.
2. Check the moisture-liquid indicator if the indicator shows a high level of moisture, the filter-drier should be
replaced.
To Replace Filter-Drier:
1. Pump down the unit (refer to Section 7.4 ) and replace filter-drier.
2. Evacuate the low side in accordance with Section 7.6 .
3. After unit is in operation, inspect for moisture in system and check charge.
7.14 THERMOSTATIC EXPANSION VALVE (TXV)
The thermostatic expansion valve (see Figure 3.2 ) is an automatic device that maintains constant superheat of the
refrigerant gas leaving the evaporator, regardless of suction pressure.
The valve functions are:
1. Automatic control of the refrigerant flow to match the evaporator load.
2. Prevention of liquid refrigerant entering the compressor.
Unless the valve is defective, it seldom requires maintenance other than periodic inspection to ensure that the ther-
mal bulb is tightly secured and properly insulated. See
Figure 7.19
NOTE
TXV Bulb Clamp is soldered to the suction line.
Figure 7.19 Thermostatic Expansion Valve Bulb
7.14.1 Checking Superheat
NOTE
Proper superheat measurement should be completed at -18
°
C (0
°
F) container box temperature
where possible.
1. Open the upper right (EFM#1) access panel (see Figure 3.2 ) to expose the expansion valve.
2. Attach a temperature sensor near the expansion valve bulb and insulate. Make sure the suction line is clean
and that firm contact is made with the sensor.
3. Connect an accurate gauge to the service port directly upstream of the suction modulating valve
4. Set the temperature set point to -18
°
C (0
°
F) and run unit until conditions stabilize.
Suction Line
Thumbscrew
TXV Bulb Clamp
TXV Bulb
Foam Insulation