For waste heat recovery process there are some thermodynamic options with efficiencies depending on some equilibrium parameters. The global warming is a permanent concern in the industries with thermal process at any temperature level. One of the promiser systems for recover waste energy from relative medium temperature level (70°C – 100 °C) is the absorption heat transformers. These thermodynamic devices are under research for several technical aspects: efficiency, corrosion, economic benefit and social impacts. These devices are a kind of heat pump: inverse absorption heat pump. The main advantage of these devices is the increment of the temperature using half part of the heat load to increase a third part of that heat at a higher temperature level (i.e., 140°C). The use of additives to achieve this process is mainly part of the success of the process. However, the control of the device is under research and development to get the higher heat recovery at the higher hemodynamic equilibrium temperature. The flow increment leads to variation of the Absorption Heat Transformer’s Coefficient of performance (COP). This variation may cause an undesirable overwarming into the absorption cycle that cause diminish of the COP and it is a risk for the thermodynamic cycle for increase of the highest-pressure zone in the process. This paper shows the thermodynamic operating conditions based on Flow Ratio calculation with the lower risk for operation based on the flow control of the refrigerant for a Carrol – Water absorption heat transformer.