First, in my decades of working on Beckman Coulter benchtop ultras, I never saw a problem like you are experiencing. The first thing I would do would be to perform both temperature and vacuum system calibrations. To do this, first close the chamber door and then enter the following keystrokes: [ENTER], 9, [ENTER], [ENTER], 100, [ENTER]. The centrifuge will beep 3 times after the calibration. Next, enter the following keystrokes: [ENTER], 9, [ENTER], [ENTER] 200, [ENTER]. The centrifuge will beep 3 times when the process is completed. As you have discovered, the temperature readout is directly related to the performance of the vacuum system. Cooling/heating of the rotor and chamber takes place via thermo-electric modules underneath the chamber assembly on what is known as the "heat sink". There is a thermistor that actually reads the temperature of the refrigeration can and ultimately the rotor after 4 hours, the two should be at the same temperature. Therefore, if you are looking to perform a run at 4 degrees, please precool the rotor to that temperature and keep the exposure of the rotor to higher temperatures while loading your samples to a minimum in order to prevent temperature rises of the rotor. If the rotor is precooled then it should not take 4 hours to get to the desired temperature. Try those calibrations and get back to me.Don