Vilter VSM 71-701 Operation And Service Manual Download

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Page 8

/ BULLETIN 10-11

flowing through the evaporator, check the piping for possible
refrigerant flow from another evaporator affecting the bulb. Re-
pipe if necessary. See Figure 4.

13. High pressure drop through evaporator

Remedy

— Check the pressure at the evaporator inlet and

outlet with gauges. If pressure difference is greater than the
values shown in Table 1, Bulletin 10-9, use an externally
equalized valve.

14. Restricted, plugged, or capped external equalizer

—

If the pressure under the diaphragm builds up due to pushrod
leakage and cannot escape through the external equalizer line,
the valve will remain closed.

Remedy

— Check the external equalizer line to be sure it is

open or not capped.

Complaint "B"

“Valve feeds too much refrigerant.”

SYMPTOMS:

■

Liquid returns to compressor.

■

Superheat is low.

■

Suction pressure is normal or higher than
normal.

THE CAUSE MAY BE:

1. Moisture

— Water or a mixture of water and oil frozen in the

valve port or working parts of the valve will prevent proper
operation. This is the most common source of trouble on TEVs.
Since the valve is the first cold spot in the system, moisture will
freeze and block the valve open, closed, or any position in
between. If the valve is held in the open position by ice, liquid
flood-back will occur.

Remedy

— Install a Sporlan Catch-All Filter-Drier in the

liquid line for removal of moisture from the refrigerant and oil.
See Bulletin 40-10.

For additional protection, install a Sporlan See•All Moisture and
Liquid Indicator for a positive indication of when a safe
moisture level is reached. See Bulletin 70-10.

2. Dirt or foreign material

— Contaminants such as copper

oxide scale, metal chips, oil breakdown sludge, etc. may pass
through ordinary strainers and lodge at the TEV port and prevent
the valve from closing.

Remedy

— Disassemble the valve and remove all foreign

material from the internal parts. Install a Sporlan Catch-All
Filter-Drier in the liquid line. The Catch-All filters out the
smallest particles of foreign material that might interfere with
the operation of any system component.

3. Expansion valve seat leak

— When the valve port does

not seat tightly, refrigerant will pass through during the off-cycle
and fill the evaporator with refrigerant. If the seat leak is severe,
the valve will feed too much refrigerant during the operating
cycle as well. (Not applicable to valves with permanent bleed
ports or RPB feature.)

Remedy

— If the valve seat is leaking, a gurgling or hissing

sound can usually be heard during the off-cycle. Also, a sight
glass or See•All in the liquid line may indicate continued refrig-
erant flow for a long period after the compressor has stopped.
Make certain however, that the bubbles are not the result of

back-flow

through a vertical liquid line.

Disassemble the valve to be certain that dirt or foreign material
is not responsible (see

B-2

). If the pin and seat are worn or

damaged and an internal parts kit is available, replace the parts.
When parts are not available, the valve must be replaced.

4. Oversized valve

— Check valve ratings considering all the

factors which affect its capacity. See Page 16, Bulletin 10-9, or
Page 3, Bulletin 10-10.

Remedy

— Install correctly sized valve.

5. Incorrect bulb installation

— The bulb should be securely

fastened to a straight, clean, section of the suction line using two
bulb straps for good thermal contact. Also, the temperature of the
bulb should not be influenced by ambient temperature — an
external heat source such as a steam pipe or heating coil.

Remedy

— Install bulb correctly. See Bulb Location and

Installation, Page 2.

6. Low superheat adjustment

Remedy

— Turn the adjusting stem clockwise until the correct

superheat is indicated. See Page 4.

7. Incorrect thermostatic charge

Remedy

— Select and install the correct selective charge. See

Bulletin 10-9.

8. Incorrectly located external equalizer

Remedy

— Relocate external equalizer or the connection

between evaporator and any other temperature or pressure
sensitive evaporator control valve near bulb location. See Page
3 for recommendations.

9. Inefficient compressor

— If the compressor is inefficient

or for some other reason lacks capacity, the suction pressure will
operate higher than normal. This may or may not be accompa-
nied by low superheats.

Remedy

— Consult with compressor manufacturer.

Complaint "C"

“Valve feeds too much refrigerant at start-up only.”

SYMPTOMS:

■

Liquid returns to compressor.

■

No superheat.

■

Suction pressure higher than normal.

THE CAUSE MAY BE:

1. Refrigerant drainage

— Drainage of refrigerant from the

evaporator (during the off-cycle) when installed at a higher level
than the compressor.

Remedy

— Install a trap-riser to top of evaporator or use

pump-down control. See Figure 5.

2. Compressor or suction line in cold location

—

During the period when the system is not in operation, liquid
refrigerant will condense at the coldest point in the system. Liquid
will condense in the compressor or suction line, if they are located
in an ambient temperature below that of the evaporator during the
off-cycle. Upon re-starting, this liquid will slug the compressor.

Remedy

— Keep compressor or suction line warm during the

off-cycle. Some compressors are equipped with crankcase heaters