Patent ID: 7215879

Claim:
A defrost heater for removing frosts sticking to a cooling device among the refrigeration cycle which uses an inflammable refrigerant comprising; a first glass tube, a second glass tube surrounding said first glass tube, a heater wire housed in the first glass tube, two plugs made of an elastic material, each of said plugs covering an opening at a respective end of said first and second glass tubes, and a lead wire passing through said plug, said lead wire connected with said heater wire at an end portion; wherein said first glass tube has an overall length that is longer than that of said second glass tube, so that, after said first glass tube and next said second glass tube are inserted at one end to one of said plugs, an other of said plugs at an other end can be fitted to said first glass tube and next to said second glass tube in a continual process; said plugs are provided with a cylindrical protrusion, which cylindrical protrusion forming at the inner wall surface a sealing contact with the outer surface of said first glass tube while at the outer wall surface a sealing contact with the inner surface of said second glass tube, a strength of the sealing contact between said plugs and said second glass tube being weaker than that between said plugs and said first glass tube; and wherein a quantity of compression caused on the cylindrical protrusion by the inner surface of said second glass tube as a result of insertion of said second glass tube is smaller than a quantity of compression caused on the cylindrical protrusion by the outer surface of said first glass tube as a result of insertion of said first glass tube.