Dry systems using thermostatic expansion valve the refrigerant management can have an evaporator or more evaporators. You should check the entire system, install manifold, and check the pressure. Check the quantity of the refrigerant through the sight glass. The following should be checked:
Liquid line solenoid valves.
Two temperature valves.
Hot gas or liquid injection systems.
Driers (both line suction and liquid line).
Pressure and temperature to the engine control.
Power supply.
You can check the evaporator and in appearance, sound and temperature of the expansion valve, if the evaporator frost back so that the suction line is frozen:
The needle may be a leak.
Control can be adjusted too little overheating.
Valve may have incorrect thermal bulb for free.
Valve with a hole can be too great
Power element can be attached loosely on the suction line.
Power element may be too warm position.
Dirt in the system by holding the valve is open.
External equalizer valve may be necessary.
The screen may be clogged.
difficult to determine which of these troubles is responsible for the problem.
The best way is to systematically check all it could be. Eliminate possible causes, one by one.
Power element location is easily checked and its attachment to the suction line said. It is recommended to place the thermostatic bulb on top of the suction line. This is a better place than next to it or under it. In this position, the liquid in the bulb makes a good thermal contact with the suction line. Fig. 15-70 shows two recommended thermal bulb places.
Rarely finds thermostatic in which someone reconfigured. So do not attempt to adjust the control in the first place. Check other troubles, instead of flowing needle or the valve may not be recoverable. It must be replaced.
Hungry evaporator gives a poor Cabinet temperature until glaze is irregular or not sweating correctly. This problem can be caused by the following:
Clogged screen to the expansion valve, which may not provide cooling.
Refrigerant loss of power element in the expansion valve, which will give an unstable ^independable) cooling.
Moisture in the system, which can sometimes give good cooling and then without cooling. Moisture will freeze in the holes for the expansion valve and close it, the defrosting.
Wax from oil in the valve. His presence means that the oil is used for various temperatures. Otherwise, it may be incorrectly prepared for cooling services.
Needle stuck shut. (This is a rare phenomenon.)
Under the capacity of the valve opening. It is usually recommended that the new valve is installed in the expansion valve gives trouble.
Sweating or frozen suction line for thermal bulb position indicates too much refrigerant flow. This condition can be caused by:
Thermal bulb escape from suction line.
Thermal bulb in the warm air flow.
TEV hole is too large.
TEV needle stuck open.
Low evaporator.
Thermal bulb wrong for free.
Pressure drop in the evaporator is too great.
If the bulb is loose or incorrectly mounted in the warm air stream, remove it. Then clean it and the tube. And mount it securely and protect it in case of need. Oversized TEV should be replaced by one of the right size. When the needle is stuck open, the best remedy is to replace the valve.
Only rarely finds the following:
In low evaporator.
In the TEV with the wrong card (to replace).
Too high pressure drop (replacement of the evaporator).
Industrial 
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