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9.8 Mechanical expansion valve
The circuit of the unit is equipped with a mechanical expansion valve,
with external equalizer
The valve is factory calibrated for an overheating of 5 °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).
Overheating calculation (S):
S = Tse - Tsa
Overheating is regulated through the expansion valve.
Make the adjusting screw follow a complete turn, and operate the
appliance for five minutes.
Check again and, if necessary, repeat the regulation.
If the expansion valve cannot be regulated, it is probably broken, and
shall be replaced. The replacement must be carried out by a Service
Centre.
9 - Maintenance (continued)
9.9 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.
