Ice-O-Matic ICE0250 series Service And Installation Manual page 56

ICE Series
Thermostatic Expansion Valve (TXV)
The thermostatic expansion valve meters the flow of refrigerant into the
evaporator changing its state from a high-pressure liquid to a low-pressure
liquid. This drop in pressure causes the refrigerant to cool. The cooled
refrigerant absorbs heat from the water circulating over the evaporator. As
the evaporator fills with liquid refrigerant, the evaporator becomes colder.
The flow of refrigerant into the evaporator is controlled by the temperature at the outlet of the
evaporator. The expansion valve bulb, mounted to the top of the suction line, senses the
evaporator outlet temperature causing the expansion valve to open or close. As ice forms on the
evaporator, the temperature drops and the flow of refrigerant into the evaporator decreases,
resulting in a drop in suction pressure.
The evaporator should become completely flooded (filled with liquid refrigerant) during the freeze
cycle. A completely flooded evaporator will have a uniform freeze pattern (ice formation across the
evaporator). A starved evaporator (not enough liquid refrigerant) will have poor or no ice formation
at the top of the evaporator, and the tube(s) exiting the evaporator will not frost. All tubes should
be within 10 degrees of each other and frosted approximately 5 minutes from the start of the freeze
cycle.
An expansion valve that is restricted or not opening properly will starve the evaporator resulting in
lower than normal suction pressure. A low refrigerant charge will also starve the evaporator and
cause low suction and discharge pressures. If not sure of the amount of charge in the system, the
refrigerant should be recovered and the correct charge be weighed in before a defective valve can
be diagnosed.
If the evaporator is starved but the suction pressure is higher than normal, the TXV is not the
problem; refer to the troubleshooting tree in section C. If the TXV sticks open or if the thermal bulb
is not making good contact with the suction line, the flow of refrigerant into the evaporator will be
too great and liquid refrigerant will flood the compressor. The suction pressure will remain higher
than normal and the machine will remain in an extended freeze cycle. Ice will build evenly but will
be very thick.
Symptom
Evaporator flooded but suction
pressure not dropping.
Compressor has been checked
and appears to be good.
Suction line at compressor may
be colder than normal
Evaporator starved, no frost
on line(s) exiting evaporator.
Suction pressure is low.
See Evap. Diagram Pg.E4
Problem
1 TXV thermal bulb not making
good contact with suction
line or uninsulated
2 TXV bulb installed incorrect
3 System overcharged
4 TXV stuck open
1 Machine low on charge
2 TXV restricted or stuck
closed
Page E3
Refrigeration System
Possible Remedy
1 Tighten bulb clamp and
insulate bulb.
2 Locate bulb on top of
suction line
3 Recharge system
4 Replace TXV
1 Recover refrigerant
and weigh in proper
charge
2 Replace TXV and
drier
Continued Page E4