The easiest way to run a test is to use the drop down list of compressor types listed in the "Select Compressor Type" field to select a compressor model that best represents the compressor being tested. Select the model type from the list and click on the "OK" button.
It is possible to create your own list that will automatically populate the report page or printout. Use the text file supplied by TDS and modify it to create your own text file. This file is named TheList.txt and is located in the C:/TDS/ directory.
Open this list in a text editor such as Notepad and you will be able add or remove compressor models. Make sure to keep the same format and the last line of the file MUST be "None,0,0,0,0".
Below is a sample of the required format:
10PA20,2000,MyPartNumber,10PA20HX234,Denso
First,150,Part1,Model1,Mfg1
Two,160,Part2,Model2,Mfg2
Three,1700,Part3,Model3,Mfg3
None,0,0,0,0
As an example the first line could be a 10PA20 compressor. The line would read:
10PA20,2000,MyPartNumber,10PA20HX234,Denso
Note: The displacement per revolution is multipliedby10 if it is a fixed displacement compressor !
When the Custom List is loaded the list supplied with the machine will be temporarily unavailable until the program is stopped and restarted. The Custom List is added by clicking on the <Add List> command button located next to the drop down list.
Performance Report Screen -After selecting the compressor type you must go to the Performance Report screen to enter the compressor clutch diameter. This measurement is in millimeters.
Once this is done you need to ensure the compressor is properly aligned. This is accomplished by moving the universal test bracket.
Press the start button.
Once the test is complete press the print button on the Setup screen. This will print the test report and save the data to disk.
Theory of Operation
A car air conditioning compressor is essentially a pump designed to move a gas through a closed system. There are many types of compressors and they come in many sizes. For the CETM to test many types of compressors the system has to be programmable so that the test dynamics for all models produce similar results within a specified range. This is accomplished by entering the displacement per revolution and the pulley diameter in the fields at the bottom of the Performance Report screen. Using the data from these fields a calculation is performed and the drive motor speed is changed to compensate for the size of the compressor.
As noted earlier, the test imitates the loads that would be put on a compressor in an actual vehicle air conditioning system. When the test is started current is sent to an air pressure transducer that adjusts the suction pressure to approximately 3 bar. This is well above the pressure which would result in a freezing evaporator and is also high enough to simulate a medium to high heat load on an evaporator. If the compressor is a variable displacement compressor the internal mechanical control valve should have been set at the factory to result in a crankcase pressure equal to the suction pressure.
The suction pressure is then adjusted down to a pressure that represents a low heat load or a freezing evaporator temperature. If the compressor is a variable compressor the discharge pressure should drop all the way down to unload the compressor. The suction pressure is then increased back to the high load condition. The discharge pressure should go up again. If it is a fixed displacement compressor the discharge pressure will drop proportionally to the suction pressure.
The discharge pressure is increased by putting a restriction in the discharge line. For this test the restriction is an adjustable orifice inside a metering valve. The pressure drop across an orifice is directly proportional to the mass flow rate. Therefore, when the compressor drops to minimum displacement the mass flow rate drops. When the machine is shipped the metering valve is set to fix the orifice size. This is done to set the maximum discharge pressure desired. All compressors should reach approximately the same maximum pressure at their maximum output. This maximum pressure can be adjusted with the metering valve. It is recommended that no changes be made to this valve.
Note: If you adjust this valve it may be necessary to adjust the "Peak" setting located at the bottom right corner of the Performance Report screen.
The "Peak" setting is the maximum pressure differential a good base line compressor will achieve. If this is set too low poorly performing compressor will pass, and if it is set too high good compressors will fail. This setting is extremely important and great care should be taken before it is adjusted.
The CETM has a frequency inverter to adjust the speed of the drive motor. This inverter also sends information to the computer on the amount of power being used during the test. Excessive power can result in poor durability of the drive motor.
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