Support
This is a
diagram from a
manufacturer
which clearly
demonstrates
the various
recommendations
in accordance to
pipe sizes.
The suction line tubing should therefore be thoroughly cleaned
to ensure good thermal contact. Of course, following on this,
it is imperative that the bulb be properly secured. I have seen
plants where the expansion valve feeler bulb is not in contact
with the suction line. Again, this will result in the expansion valve
opening, possibly allowing a liquid flood back to the compressor,
and again this can and does result in compressor failure.
Always insulate the entire sensing bulb after installation. An
accurate temperature reading of the suction line and the suction
line only is needed. Ambient temperatures surrounding the feeler
bulb will negatively impact on the accurate operation of the
expansion valve.
INSTALLATION MISTAKES TO AVOID
specified whilst on small diameter tubing the twelve, one o'clock
position is used.
The reason we don't place the sensor bulb on the bottom
of the suction line is that oil travelling along the bottom of that
tubing can act as an insulator to prevent the sensor bulb from
accurately sensing the temperature of the refrigerant.
It then stands to reason that one should never attach the
feeler bulb, or any sensor for that matter to the bottom of the
refrigerant tubing (six o’clock position). In addition, never place
the bulb downstream of a P-trap. Bulb placement before a P-trap
(upstream) is recommended.
In some instances, one can install the feeler bulb in the vertical
position, however this is not ideal and only should be done when
one has no other option.
When putting the bulb on a vertical line it is imperative to
have the tail end up. The reason for this is to ensure that the
refrigerant charge in the bulb stays in the bulb. This allows for
a better reaction to changes in the suction line temperature.
When clamping the bulb at the 4 or 8 o’clock positions on larger
horizontal lines, keep the tail rotated so it is always down to keep
the charge in the bulb.
Sarel, if multiple expansion valves are installed, each
thermostatic expansion valve has to be installed on the
refrigerant suction line corresponding to that particular portion of
the evaporator to control conditions in each individual evaporator
or portions thereof. Never place any of the feeler bulbs on the
common header of the suction line fed by multiple evaporators.
THERMAL CONTACT
It is extremely important that the feeler bulb be installed with
good thermal contact. I have often seen that the bulb is installed
on dirty tubing. The debris creates an insulating barrier preventing
the bulb from accurately sensing the actual suction line
temperature. This would result in the expansion valve opening,
possibly allowing liquid flood back to the compressor. This can
and does result in compressor failure.
60
RACA Journal I April 2020
A TEV sensor that is too loose or has a poor thermal contact to
the suction line can send incorrect signals to the TEV and can
cause liquid refrigerant flood back damage to the compressor.
The sensing bulb must also not be exposed to external
sources of heat or cold such as a warm air current. Insulation
should be applied to protect the bulb from any external
influence.
Most installation guides require that the system has nothing
installed on the refrigerant tubing that extends between the TEV
and the evaporator coil, except in the case when installations
have a refrigerant distributor installed. In this case an externally
equalised expansion valve is used.
A poorly installed or incorrectly
adjusted valve can most certainly
cost you a compressor.
The temperature sensing bulb should never be placed at the
bottom or under-side of the suction line, a situation that will
cause improper reading of the line's temperature, thus causing
inaccurate TEV operation.
Avoid where possible, installing TEV temperature sensing
bulbs on vertical piping.
Do not install the sensor bulb on a common suction manifold.
Follow the manufacturer’s instruction as where to install the
feeler bulb, as a general rule: 12 o’clock for suction lines 19mm
and smaller and four o’clock for larger than 19mm.
On an installation it is also important that the TEV be installed
in a location allowing access to adjust the device.
HUNTING THERMOSTATIC EXPANSION VALVES
The definition of hunting expansion valves is a valve that is
cycling too frequently between open and closed. This condition
may be detected by observing suction line pressure. Rapid
www.hvacronline.co.za