Ken. I can almost answer the question in one word. HEAT. From the current draw of the fans. How many miles on the fans may have the brushes worn down and they will draw more current which produces heat. I wouldn't keep adding higher current breakers, you may be masking a problem and burn up some wires. This is why I don't use circuit breakers in the fan circuit of The Fan Fix, I fuse at 15 amps and in most cases will handle the load. If you have any current measuring equipment, the fans ( both ) coming on will surge at around 60 amps and run ( both ) at 28 to 30. 1/2 for ea fan. You may have one or both fans running sluggish and drawing more current. John Hervey www.specialTauto.com << I've come across a problem I've not been able to solve. The circuit breaker to the cooling fans keeps tripping when the air conditioner or the otterstat has them switched on. It happens after the car and fans have been running for a while and the breaker has become hot. I thought I may have just had an old or defective breaker (40 amp) but the replacement does the same thing. I have a FanZillia, the fuses on it are holding and both fans turn easily. Why are they drawing so much current? I'd just jump the breaker and rely on the fuses but That's just not a good answer. >>