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John ED Renstrom
06-23-2016, 01:28 AM
don't use to big a fuse in the holder. we have been having some trouble with the AC in the 72 cb. it has the comfortron automatic system in it and to say that it's qurkie is a understatement. any way searched around till I found the main vacuum leak to get the controls to work properly. then the intermittent problem with the fan became a permanent problem. so under the hood we go. all the relays were working so we checked the power wire. I remember when I got the car it has a inline fuse that the holder had melted . I did replace it but only had a fuse to small for the blower so I put in this 30 amp. I knew the motor would never trip it. I was right. looks like the holder was not rated at the amperage the motor will draw. it has started arcing on the far side and kept it up till it melted the blade on the fuse. the fuse never blew. as long as the leg was making connection with it's melted part it would come on. . needless to say we went down a bought a holder that would carry the load and removed the quick disconnect in line also. after all every connection is a resister. then put in the proper 25 amp fuse. now we have air and air movement.

Paul Steinberg
06-23-2016, 11:06 AM
I would install a high amperage relay in that fused line, and take the power from the battery through the relay to the fan motor. The problem exists, because GM knew that as long as all the parts were new, and the connections were perfect, that it wouldn't blow the fuse. Now that some of the connections have corrosion on them, and the blower motor is tired and draws more amperage, it will blow the fuse. A relay is the only way that you are going to be able to have a long term fix to this problem.

John ED Renstrom
06-23-2016, 12:20 PM
this was the power feed to the relay that did this.

Peter Grave
06-23-2016, 12:37 PM
I second Pauls motion on this back in the day GM police cars had the same issue. We had melted fuse holders bad blower motors etc from resistance and low voltage.The blower motors have a HEAVY draw especially as they get older. You need heavy gauage wire for the supply to the relay and from the relay to the motor this keeps all operating without heat up and resistance. Not so much Cadillacs as Olds and Pontiac were prone to under hood fires in this era.