Are the settings of temp correct? Check back panel, is it clean, remove back panel, AFTER disconnecting from mains. look inside, you will see a motor, that is the compressor. a fan near it, check it, make sure it is clean nothing obstructing it. Keep all that area clean. Other than that, you would need test equipment, to test the various temperature sensors. There are a few of them. plus heaters, Yes you have heaters, they do the auto defrost. Other than the basic checks above, Very difficult to diagnose without taking reading from sensors, etc there is some service code, that is possible to access, but does not tell you much, sometime which sensor, But I cannot remember the code, It varies from model to model. Try the basics first, otherwise might need to call an engineer. faulty part, but which.
SD, July 2011
