Systems and methods can provide an optical transmittercombiner having improved isolation and signal to noise ratio performance. The low-pressure cleaning system discharges air at a low pressure, high velocity, and a high volume in order to clean the heat exchanging coil. The plurality of vending transaction data is stored in a memory of a vending apparatus, and is encrypted. The information provided to the user can help a user compare a variety of alternative modifications in order to select the modifications that are efficient and effective. In other aspects, operation of the engine is adjusted based at least in part on the determined pressure in the combustion chamber. The administration unit notifies the connection relay apparatus for the target shared device of permission for transfer of data between the target client and the target shared device, together with information identifying the target client.