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Since you have quoted that you have already vacuumed the condenser unit from the back and had already removed all dust & lint from the condenser unit so that possibility should be ruled out. The Poor cooling that you are facing could also be (In fact the most common reason) due to the result of a heavy frost build-up on the evaporator coils. You can't see these coils without removing/opening the panel on the inside of your freezer. A sure sign that there is a build-up is the presence of any frost or ice build-up on the inside walls, floor, or ceiling of the freezer that is exactly the thing you quoted. Such a frost build-up usually shows a problem in the self-defrosting system or damaged door gaskets.
The refrigerator is supposed/designed to self-defrost approximately four times in every 24 hour period. If one of the components in the self-defrosting system fails, the refrigerator continues to try to cool. Eventually, though, so much frost builds up on the evaporator coils that the circulating fan can't draw air over the coils. There may still be a small amount of cooling because the coils are icy, but with no air flow over the coils, cooling in the refrigerator compartment is quite limited.
Here's an inexpensive, though inconvenient, way to determine if the problem is with the self-defrosting system. Remove all of the perishable food from the refrigerator and freezer, turn the thermostat in the refrigerator to Off, and leave the doors open for 24 to 48 hours. (Be sure to have several towels ready in case the melting frost and ice causes the drip pan to overflow). This allows the refrigerator to defrost "manually." When the frost and ice build-up has completely melted away, turn the thermostat back to a normal setting. If the refrigerator then cools properly, it indicates a problem with one of three components in the self-defrosting system:
The defrost timer
The defrost thermostat (usually a bi-metallic switch)
The defrost heater
If it still does not cool properly, there may be a problem with the refrigerant level or the compressor.
If the problem still persists and the above quoted techniques/tips didn't work,You may need a qualified appliance repair technician to further diagnose the problem.
Best of Luck,
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on Aug 10, 2010