External Equalizer Connection; Oil Return Connection - Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual

VERTICAL MOUNTING
(Preferred Method)
SIZE EACH
SECTION FOR
80 EQUIVALENT FT.
SIZE DOWN
MIN 15 DIAMETER
MIN 10 DIAMETER
EXTERNAL EQUALIZER
Thermostatic expansion valves with an external equalizer con-
nection will not work unless the connection is made to the suc-
tion line. The connection should be made at a point close to
and directly downstream of the sensing bulb where the pres-
sure can be properly sensed. The connection should not be
located where a trap is in the suction line between the sensing
bulb and the equalizer connection. If the connection is made on
a horizontal section of the suction line, the connection should
be made at the top of the tube. Equalizer connections on verti-
cal risers should be at least 10 pipe diameters above the start of
the riser.
Most TXVs used on larger evaporators are externally equal-
ized. This line only provides pressure feed back to the TXV
and does not allow refrigerant flow into the TXV. System pres-
sures will not equalize through this line. Figure 100 shows
good mounting locations.
If any evaporator pressure or temperature control valves are
located in the suction line at or near the evaporator outlet, the
equalizer must be connected on the evaporator side of these
valves.
OIL RETURN CONNECTION — If the evaporator coil is
supplied with an oil return connection at the bottom of the suc-
tion header, this small connection must be teed in ahead of the
first mixing elbow and before the TXV bulb as shown in Fig.
100. The oil return line should be kept small in diameter; a
in. line will suffice in most cases. It is not necessary, when the
compressor is below the evaporator, that the riser at the evapo-
rator extends at least as high as the top level of the evaporator;
after the 15-diameter riser has been provided, the suction line
may elbow down immediately.
Piping loops serve to control oil accumulation in idle coil
sections and prevent off cycle drain back. When the compres-
sor is located below the evaporator the suction header should
be extended above the highest point of the evaporator circuit
before dropping to the compressor.
EXPANSION VALVE ADJUSTMENT — Each Sporlan
TXV is thoroughly tested and set at the factory before
HEADER
COIL
MIN 8 DIAMETER
Fig. 100 — Refrigerant Piping Detail
CONNECTION —
1 / -
4
129
2 ELBOWS
DROP BELOW
TXV BULB
REMOTE BULB ON SMALL SUCTION LINE
(LESS THAN 7/8 IN.)
shipment. The factory superheat setting will be correct and no
further adjustment is required for the majority of applications.
How to Determine Superheat Correctly
1. Measure the temperature of the suction line at the bulb
location.
2. Obtain the suction pressure that exists in the suction
line at the bulb location by either of the following
methods:
a. If the valve is externally equalized, a gage in the
external equalizer line will indicate the desired
pressure directly and accurately.
b. Read the gage pressure at the suction valve of the
compressor. Add the estimated pressure drop
through the suction line between bulb location and
compressor suction valve to the pressure. The sum
of the gage reading and the estimated pressure drop
will equal the approximate suction line pressure at
the bulb.
3. Convert the pressure obtained in Step 2a or 2b above
to saturated evaporator temperature by using a
temperature-pressure chart.
4. Subtract the two temperatures obtained in Steps 1 and
3 — the difference is superheat.
How to Change the Superheat Setting — The valve should
be set with the system as near as possible to design conditions.
To reduce the superheat, turn the adjusting stem counterclock-
wise. To increase the superheat, turn the adjusting stem clock-
wise. When adjusting the valve, make no more than one turn of
the stem at a time and observe the change in superheat closely
to prevent over-shooting the desired setting. As much as 30
minutes may be required for the new balance to take place after
an adjustment is made.
NOTE: Some valve bodies (G, EG, C, S, EBS and EMC)
have a packing nut around the adjustment stem. It may be
necessary to loosen the packing nut slightly to turn the
adjusting stem. Do not forget to retighten the nut after the
superheat is set.
HORIZONTAL MOUNTING
EXTERNAL
EQUALIZER
LINE
OIL
RETURN
CONNECTION
BULB MOUNTING
(SEE DETAIL A)
DETAIL A
a39-3971