The invention relates to a braking device for a motor vehicle fitted with an air conditioning circuit (K), this braking device comprising a source of fluid (F1) at a relatively high pressure, a source of fluid (F2) at a relatively low pressure, and a pneumatic brake booster (F3) selectively connected to one or other of the sources of fluid (F1, F2).According to the invention, the source of fluid (F1) at a relatively high pressure comprises a portion (KC1) of the air conditioning circuit (K) that is placed downstream of the air conditioning compressor (K1) and upstream of the air conditioning expansion valve (K2), in one direction of flow (X) of the cooling fluid in the air conditioning circuit (K).