I went thru similar problem with my hybrid 190 E36 --- what A/C tech found was an air lock in the system. You should try all the tensioning suggestions posted earlier, then have someone evacuate your a/c system .. pull vacumn and refill ... then try the system, and check for leaks using uv dye. If that fails to improve, then ask tech to check the dryer- reciever, and high pressure switches. If not those items, then check the Klima relay... hope this helps .. lemme know.