icetro IM Series, Technician'S Handbook

Page: 82 / 166

5. Testing the Expansion Valve
The expansion valve (TXV) is designed to modulate the
flow of refrigerant, depending upon the needs of the
evaporator.
Extremely thin ice at the evaporator outlet could be a sign
that the machine is undercharged or that the TXV is
starving the evaporator for refrigerant.
Similarly, extremely thin ice at the evaporator inlet could
be a sign that the machine is overcharged or that the TXV
is flooding the evaporator with refrigerant.
To test the TXV, remove the sensing bulb from the suction
line, just after the evaporator outlet. While watching the
low-side on the manifold gauge set, hold the bulb tightly
in you hand and watch to see if the low-side pressure
begins to rise, indicating more refrigerant is entering the
evaporator.
Next, place the bulb in a cup of ice water and watch to
see if the low-side pressure drops again, indicating less
refrigerant is entering the evaporator.
81