14Part number 21729, Rev 4Using a 250 Ω resistor, the voltage drop across the resistor varies with temperature per thefollowing equation.Temp (C) = - 34.75 (Vdrop) + 74.75See the table below for representative readings.Voltage (VDC) Chamber temperature ( 0C)1.58 202.15 03.59 -504.46 -80Maintenance intervalsMaintenance item Recommended intervalPre-Filter and Condenser 3 monthsCalibration 1 yearBattery 1 yearDoor gasket and vacuum relief port Monthly minimumDefrost As neededMaintenance proceduresAir filterIn most laboratory conditions, the air filter should be inspected monthly and cleaned once everythree months. Press the top of the filter cover to release the catch. The door will swing forwardallowing easy access to the washable pre-filter.CondenserAnytime that the air filter is removed for cleaning, the condenser fins and coils should beinspected for dust that impedes the flow of air over the coils. Such dust should be removed witha vacuum cleaner. The fins on the heat exchanger are very delicate and are easily bent, so be sureto avoid placing any pressure or impact on the fins while cleaning.