4-3
4.2 SUCTION AND DISCHARGE SERVICE VALVES
The suction and discharge service valves used on the
compressor are equipped with mating flanges for
connection to flanges on the compressor. These valves are
provided with a double seat and a gauge connection, which
enable servicing of the compressor and refrigerant lines.
Turning the valve stem clockwise (all the way forward)
will frontseat the valve to close off the suction or discharge
line and opens the gauge connection to the compressor. See
Figure 4-3. Turning the valve stem counterclockwise (all the
way out) will backseat the valve to open the suction or
discharge line to the compressor and close off the gauge
connection.
With the valve stem midway between frontseated and
backseated positions, suction or discharge line is open to
both the compressor and the gauge connection.
For example, when connecting a manifold gauge to
measure suction or discharge pressure, the valve stem is
fully backseated. Then, to measure suction or discharge
pressure, crack open the valves 1/4 to 1/2 turn.
Gauge Connection
Valve Cap
Valve Stem
To Suction or
Discharge Line
Compressor
Valve
Frontseated
(clockwise)
Valve
Backseated
(counterclockwise)
Figure 4-3. Suction or Discharge Service Valve
4.3 PUMPING THE UNIT DOWN OR
REMOVING THE REFRIGERANT
NOTE
To avoid damage to the earth’s ozone layer, use
a refrigerant recovery system whenever removing
refrigerant. When working with refrigerants you
must comply with all local government
environmental laws, U.S.A. EPA section 608.
a. Pumping the Unit Down
To service the filter-drier, moisture-liquid indicator,
expansion valve, suction modulation valve, suction solenoid
valve or evaporator coil, pump most of the refrigerant into
the condenser coil and receiver as follows:
1. Install gauges and mid seat the suction and
discharge valves (turn clockwise) as specified in section
4.1.a.
2. Allow the compressor to run 10 to 15 minutes.
Then close (front seat) liquid line valve by turning
clockwise. Start the unit and run in a cooling mode. Place
start-stop switch in the OFF position when the unit reaches
and maintains a positive pressure of 0.1 kg/cm
@
(1.0 psig).
NOTE
The unit may need to be cycled several times to
achive this reading.
3. Frontseat (close) the suction service valve and the
refrigerant will be trapped between the compressor suction
service valve and the liquid line valve.
4. Before opening up any part of the system, a slight
positive pressure should be indicated on the pressure gauge.
If a vacuum is indicated, emit refrigerant by cracking the
liquid line valve momentarily to build up a slight positive
pressure 0.1 kg/cm
@
(1.0 psig)..
5. When opening up the refrigerant system, certain
parts may frost. Allow the part to warm to ambient
temperature before dismantling. This avoids internal
condensation which puts moisture in the system.
6. After repairs have been made, be sure to perform
a refrigerant leak check (section 4.4), and evacuate and
dehydrate the system (section 4.5).
7. Check refrigerant charge (Refer to section 4.6).
4.4 REFRIGERANT LEAK CHECKING
WARNING
Never mix refrigerants with air for leak testing. It
has been determined that pressurized, air-rich
mixtures of refrigerants and air can undergo
combustion when exposed to an ignition source.
a. The recommended procedure for finding leaks in a
system is with a R-134a electronic leak detector. Testing
joints with soapsuds is satisfactory only for locating large
leaks.
b. If the system is without refrigerant, charge the system
with refrigerant to build up pressure between 2.1 to 3.5
kg/cm
@
(30 to 50 psig). Remove refrigerant cylinder and
leak check all connections.
NOTE
It must be emphasized that only the correct
refrigerant cylinder be connected to pressurize the
system. Any other gas or vapor will contaminate
the system which will require additional purging
and evacuation of the system.
c. Remove refrigerant using a refrigerant recovery system
and repair any leaks.
d. Evacuate and dehydrate the unit. (Refer to section 4.5)
e. Charge unit per section 4.6.
4.5 EVACUATION AND DEHYDRATION
4.5.1 General
Moisture is the deadly enemy of refrigeration systems.
The presence of moisture in a refrigeration system can have
many undesirable effects. The most common are copper
plating, acid sludge formation, “freezing-up” of metering
devices by free water, and formation of acids, resulting in
metal corrosion.
4.5.2 Preparation
a. Evacuate and dehydrate only after pressure leak test.
(Refer to section 4.4)
Downloaded from
