ICE SeriesRefrigeration System
Thermostatic Expansion Valve (TXV)
The thermostatic expansion valve meters the flow of refrigerant into the evaporator changing its state from a
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 | Problem | Possible Remedy | ||
Evaporator flooded but suction | 1 | TXV thermal bulb not making | 1 | Tighten bulb clamp and |
pressure not dropping. |
| good contact with suction |
| insulate bulb. |
Compressor has been checked |
| line or uninsulated |
|
|
and appears to be good. | 2 | TXV bulb installed incorrect | 2 | Locate bulb on top of |
Suction line at compressor may |
|
|
| suction line |
be colder than normal | 3 | System overcharged | 3 | Recharge system |
| 4 | TXV stuck open | 4 | Replace TXV |
Evaporator starved, no frost | 1 | Machine low on charge | 1 | Recover refrigerant |
on line(s) exiting evaporator. |
|
|
| and weigh in proper |
Suction pressure is low. |
|
|
| charge |
See Evap. Diagram Pg.E4 | 2 | TXV restricted or stuck | 2 | Replace TXV and |
|
| closed |
| drier |
Continued Page E4
Page E3
