Pitting corrosion behaviors for carbon steels in the working fluid for absorption heating and refrigerating systems were investigated. The fluid was an aqueous solution of 60% LiBr+0.2%LiOH+0.2%Li2CrO4. The testing temperature was 150°C which was 4°C below the boiling point. The critical depth concept which was developed for stainless steels in neutral chloride solutions was applied. The Vc, pit, Ez and ER, pit were measured to be -490, -540 and -550mV, respectively. For potentials above Vc, pit, pits initiated and continued to grow. For potentials between Vc, pit and Ez, the passive film broke down but the resulting depressions were found to repassivate before exceeding the critical depth r* which was determined to be 20μm. Nevertheless, pits deeper than 30μm continued to grow for potentials above ER, pit. When a carbon steel merely immersed in the solution, micro-pits which were shallower than r* generated intermittently at potentials above Ez. The dissolution current prevented the Ecorr from ennobling above the Vc, pit, and consequently the initiation of a growing macro-pit was inhibited. However, when carbon steel was held at -800mV for more than 10h in the solution prior to the open-circuit immersion, one growing macro-pit initiated during the initial period of the immersion. Because the resistance to film breakdown and cathodic reaction on the steel surface were increased with the pretreatment, the open-circuit potential for the initial period was maintained more noble than Vc, pit and one pit grew beyond r* before the Ecorr fell below Vc, pit. The pit was found to continue growing at the following Ecorr which was maintained above ER, pit.