Can the quanity of freon, 134 be checked by pressure readings, hi and lo side? 124 300 TD. What should these pressures be if correct amount of freon is in the system?

There are several reasons to have the 'compressor cut off' temperature (as measured by the evaporator temp sensor) a ways above 32F. First is the fact that the ETS does not measure the actual surface temp of the evaporator tubes. It will always be a little warmer. Then there is a small 'production tolerance' in the individual ETS units. The goal is to keep the evaporator from icing up under conditions of low air flow -like when its 40F outside and you need to dehumidify (defog) the inside of the car. The ON/OFF EST switch system is not a very good way to achieve steady or precise evap temp control. A cycling evap temp is one reason so many MBZ evaporators fail--continual expansion/contraction. Temp cycling causes fatigue cracks. A far better system uses a throttling expansion valve which senses both evaporator operating pressure AND temperature. This allows one (The designer)to 'set' the evaporator inlet or outlet temperature at what works best for the particular installation. I once had a Imperial LeBaron, which had front and rear evaporators, and Chrysler had a VERY smooth temperature control system on that baby--throttling expansion valve on the evaporator INLETS AND an electrically operated compressor suction throttling valve-- with that valve working off a sesitive temperature sensor on the evaporator outlet lines --. That way they could drive the evaporators right to freezing (actually 33F) on inlet and outlet to maximise performance. The AC worked 'at maximum capacity for the air flow and temp conditions' with re-heat to modulate cabin temp, and variable outside air intake to modulate relative humidity!

However, with fuel economy penalties,etc, such a thermally inefficient system is not gonna happen in a measely $65K car. You are gonna be stuck with a minimal capacity system designed to use the least amount of engine power to meet the 'requirements.' Passenger comfort considerations seems to be forgotten, or certainly lower in importance, even in these very expensive 'luxury' cars.

OH, what some would give for a good old GM/Fridgedaire A-6 TXV/reheat system. MBZ actually licensed that system from GM in about 1975, just like they licensed automatic transmission shifting technology from GM Hydramatic Div--because GM had a much better systems and their technical know-how was the best in the world.

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