Sight Glass; Electronic Expansion Valve; Evaporator - comatec AQWL Installations- Und Wartungshandbuch

9.8 Sight glass

The sight glass is used for inspecting the refrigerant flow and the
humidity % of the refrigerant. The presence of bubbles indicates that
the dehydrating filter is clogged or the charge insufficient.
A colour indicator is positioned inside the sight glass. If you compare
the colour of the indicator to the scale on the ring of the sight glass,
you can calculate the percentage of humidity of the refrigerant. If it
is excessive, replace the filter's cartridge, operate the appliance for
1 day and then check the humidity % again. When the humidity % is
within the pre-determined range, no other operations are required. If
the humidity % is still too high, replace the dehydrating filter again,
start the unit and operate it for another day.

9.9 Electronic expansion valve

The circuit of the unit is equipped with electronic expansion valve.
The valve is calibrated for an overheating of 6 °C.
Procedure to check for overheating:
– Measure the suction pressure with the pressure gauges on the
board of the unit o using a pressure gauge connected to the
service valve on the suction side.
– From the pressure gauge's temperature scale, measure the
saturated suction temperature (Tsa) which corresponds to the
pressure value.
– Using a contact pressure gauge affixed to the outlet fitting of the
gas of the evaporator, measure the actual temperature (Tse).
9 - Maintenance (continued)
Overheating calculation (S):
S = Tse - Tsa
Overheating is regulated through the expansion valve.
If the electronic expansion valve cannot be regulated, it is probably
broken, and shall be replaced. The replacement must be carried out
by a Service Centre.

9.10 Evaporator

Check at regular intervals that the water side of the heat exchanger
is perfectly clean. To do this, measure the pressure drop, water side
(see Section 8) or measure the temperature of the liquid leaving
and entering the heat exchanger, and compare it to the evaporation
temperature.
To obtain an effective heat exchange, the difference between the
temperature of the leaving water and the saturated evaporating
temperature must be in the 2 - 4 °C range. A greater difference
would indicate a low efficiency of the heat exchanger (i.e. the heat
exchanger is dirty).
In this case, the heat exchanger must be subjected to chemical
cleaning, an operation that shall be carried out by authorised
engineers.
For other maintenance operations (extraordinary overhauling,
replacement of the heat exchanger etc.), contact an authorised
Service Centre.
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