The glue is usually needed if the clutch gap increases, allowing the clips to fall out when the clutch is engaged. If using 2 clips, glue them together first, then apply glue to both sides and slide the pair back into position.

If one clip falls off, the clutch and bearing will suffer. It does not get hot enough to melt the plastic or glue.

The bread clips will last a while, depending on how much the compressor cycles. It is NOT a weak electromagnet, just a lot of wear on the clutch surface. Remember, the American car compressors are designed to be on all of the time and the blend doors provide heat to keep the cabin temp at the desired level.

The American cars used to have AC only from the top dash vents, European cars delivered cold air from all 3 levels.
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Keeping it running is better than buying new