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 may be too large.
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.
Industrial 
..