In the system in the condensor and evaporator is the refridgerant present as liquid and gas, This means that the temperatures are directly connected to the pressures and measuring the temperature will tell you the pressure at these locations. As you can see from the blue temperature lines when liquid and gas are both present the temperature will remain constant at the same pressure.
In general the liquid/gas mixture should be present in most parts of the evaporator and condensor. If too much gas is filled in the system the liquid is accumulating in the condensor and filling it up with liquid. If this is the case you will find a level where there is a sharp drop in temperature indicating up to where the condensor is filled with liquid. The part of the condensor filled with liquid does not contribute to the condensing of the gas anymore and overheating might occur in the upper part of the condensor causing the pressure to rise too high and your pressure switches to cut out the compressor clutch.
If not enough gas is present then the overall pressure of the system in the condensor will be lower then the measured temperature as it is not possible to get a stable situation as the liquid (possibly mixed with some gas)is imediately sucked out by the compressor through the expansion valve.
If the expansion valve is faulty you will get too low pressure in your evaporator as not enough liquid is let in. This will cause extreem low temperatures and the clutch will disengage frequently to avoid freezing.
To check the system you should get hold of an infrared thermometer with a laser pointer and check temperatures alover the condensor.