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© STULZ S.p.A. – all rights reserved EN/06.2016/i09
WSA ExplOrEr OriginAl inStructiOnS
8.3.8 Expansion valve
The refrigerant circuit is equipped with a electronic expansion valve, which controls the
super-heating in the evaporator. The super-heating is adjusted to 5 K at the factory and may not
be modified. Check the super-heating set-point.
Check the super-heating by the C2020 electronic controller. If the super-heating is for a longer
time below 3 K or above 7 K, the function of the expansion valve is faulty.
Compare the suction gas temperature measured by the valve sensor, with the value of a refer-
ence sensor at the suction line. If the super-heating still diverges significantly from the set-point
and you can find no deviation at the verifications, probably the control module of the valve is
defective and must be replaced.
The expansion valve can freeze, if the humidity in the refrigerant circuit is excessive. Check the
sight glass.
WArning
Do not thaw by soldering flame, danger of explosion! Thaw with moist warm cloth. Check the
sight glass.
8.3.9 compressor
To be checked: compressor, crankcase heater
In the screw compressor, there are three main components which require inspection and mainte-
nance. The integrated oil filter is maintenance-free.
pressure relief valve
The pressure relief valve has a response pressure difference of 28 bar and is maintenance-free.
Repeated opening of the valve due to abnormal operating conditions, however, may result in
steady leakage. This can be detected by a reduced output and a high discharge gas tempera-
ture. If is this the case, replace the valve.
check valve
To protect the compressor against reverse rotation during standstill a check valve is installed
under the discharge shut-off valve resp. below the pipe connection. If the compressor runs in
reverse direction for more than approximately 5 sec. after the cut-off, the valve may be defective
and must be replaced. A reverse rotation of the compressor can be detected by an abnormal
sound.
roller bearing
The screw compressors are equipped with fatigue endurable roller bearings. The bearings can
be checked by means of a sound analysis. If the bearings must replaced, also the rotors, the
housing and the discharge flange should be checked visually. In case of severe scores or abnor-
mal abrasion, a major overhaul of the compressor or its replacement is advisable .
auxiliary contactor in the electric cabinet. For the 140W heater the ohmic resistance should
approximately be 1,1 kOhm, 1,3 kOhm for the 120W heater and 1,8 kOhm for the 90W heater.