Thanks for the vehicle info...it definitely helps us to help you better.
If the engine isn't regulating or maintaining the correct temperature (coolant system)...it can have an affect on the HVAC system in that the aux cooling fan (in front of the radiator & directly behind the kidney grills) receives a signal from the ECM/ECU/DME when certain criteria is met from the radiator outlet temperature, vehicle speed, battery voltage, AC pressure, and catalytic converter temperature (see info below). Did you check to see if it is operating (the aux fan)?
Cooling system hoses for the M54 engine (click link below to get BMW 11 digit part nbrs for the items in the diagram)...or you may find some forum sponsoring vendors or others may sell an M54 engine cooling system hose kit (try googling
BMW M54 COOLING HOSE KIT) to see if any vendors come up in a search like that.
