Indianapolis suffered a weeks worth of extremely high temps, 100+ thru the last weekend. I replaced about $30 worth of 30A fuses.
I believe the failure is occurring while the system is running. Each time I replaced a fuse the system started up at the "cool" command from the thermostat. During the highest of the heat wave, 104 Saturday evening with each new fuse the system ran 45 minutes to an hour before failure.
The system is a 12 year old 6 ton Crane residential split system. Electric is supplied thru a pair of 30A breakers to a 30A fused disconnect.
House is a 1901 Arts & Crafts Victorian -- so insulation is minimal,system got little down time during the heat wave.
Today the temps dropped back to normal, 80's, it has run all day, cycling, without a problem.
Something I did notice, a difference in the fuses. One never failed, no matter which leg it was installed in, a GE FP35-89. All the failed fuses are Buss FRN-R-30. I looked for more of the GE fuses at the big box stores without success.
I do know that on motor circuits larger amp fuses can be installed after the breakers. The 30A fuses are the largest available for the current disconnect. I have not yet located any label supporting a larger fuse.
Any advice would be appreciated, thanks