6--13
T-334
c. Connect an accurate gauge to the service port direct-
ly upstream of the suction modulating valve
d. Set the temperature set point to -18C (0F), and run
unit until conditions stabilize. Partially block the con-
denser airflow with cardboard or similar material and
raise the discharge pressure to above 175 psig
(12 bar).
NOTE
For units operating in high ambient tempera-
tures, blocking the coil may not be required; the
pressure inside the unit may already be above
the required condition.
e. The readings may cycle from a high to a low reading.
Take readings of temperature and pressure every
three to five minutes for a total of five or six readings.
f. From the temperature/pressure chart (Table 6--8),
determine the saturation temperature corresponding
to the evaporator outlet test pressures at the suction
modulation valve.
g. Subtract the saturation temperatures determined in
step f. from the temperatures measured in step e. The
difference is the superheat of the suction gas. Deter-
mine the average superheat. It should be 4.5 to 6.7C
(8 to 12F).
6.12.2 Valve Replacement
a. Removing an Expansion Valve
NOTES
1. The TXVs are hermetic valves and do not
have
adjustable
superheat.
(See
Figure 6--12 and Figure 6--13.)
2. All connections on the evaporator TXV are
bi-metallic, copper on the inside and
stainless on the outside. When brazing,
bi-metallic connections heat up very
quickly.
1
6
5
4
3
2
1. Evaporator Expansion Valve
2. Non-adjustable Superheat Stem
3. Equalizer Connection
4. Inlet Connection
5. Outlet Connection
6. Expansion Valve Bulb
Figure 6--12 Evaporator Expansion Valve
1
2
1. Inlet
2. Outlet
Figure 6--13 Economizer Expansion Valves
1. Pump down the unit per paragraph 6.3.2. Evacuate if
unit is not equipped with service valves. Refer to
paragraph 6.4.4.
2. Remove cushion clamps located on the inlet and out-
let lines.
3. Remove insulation (Presstite) from expansion valve
bulb.
4. Unstrap the bulb, located below the center of the
suction line (4 o’clock position), and remove the
valve.
b. Installing an Expansion Valve
1. Braze inlet connection to inlet line, see Figure 6--14.
2. Braze outlet connection to outlet line.
3. Braze the equalizer connection to the equalizer line.
4. The economizer valve should be wrapped in a
soaked cloth for brazing. (See Figure 6--14). Braze
inlet connection to inlet line.
5. Braze outlet connection to outlet line.
6. Reinstall the cushion clamps on inlet and outlet lines.
7. If applicable, braze the equalizer connection to the
equalizer line.
8. Check superheat (refer to step 6.12.1).
6.13 EVAPORATOR COIL AND HEATER
ASSEMBLY
The evaporator section, including the coil, should be
cleaned regularly. The preferred cleaning fluid is fresh
water or steam. Another recommended cleaner is
Oakite 202 or similar, following
manufacturer’s
instructions.
The two drain pan hoses are routed behind the
condenser fan motor and compressor. The drain pan
line(s) must be open to ensure adequate drainage.
6.13.1 Evaporator Coil Replacement
a. Pump unit down. (Refer to paragraph 6.3.2.) Evacua-
te if unit is not equipped with service valves. Refer to
paragraph 6.4.3.
b. With power OFF and power plug removed, remove
the screws securing the panel covering the evapora-
tor section (upper panel).
c. Disconnect the defrost heater wiring.
d. Remove the mounting hardware from the coil.
e. Unsolder the two coil connections, one at the distribu-
tor and the other at the coil header.
Downloaded from
