[thisnametooktolong]

Before I started replacing anything lets assume (ass-of-U-me) that the Motor is good far a second. An auto motive fuse is usually a 5 second delay at the rated current. So if that fan runs on low and pops a 30 amp fuse like a flash bulb its drawing about 40+ amps. IF it takes about 30seconds it is around 29+ amps and that could be the new motor and or a wire problem.
With the motor unplugged (checking good or bad) go to the High speed blower relay that should be in the relay control center. Yank that puppy out and inspect its general condition comparing it to like relays in the box. Does it look like it was hot? Are the pins nice and shinny?
If you have a noide light, start checking for shorts by connecting one end of the light to the + bat voltage and probing the connector for the relay. With the fuse pulled all of the big pins on relay connector should be open (a VOM is a better choice). With the key off and the climate off the coil contacts should also be open. (but the coil contact runs off the low speed ckt and should not matter) Then check what I mention below. I list a step by step process without a light or VOM but the order and points are the same.

With the relay and motor disconnected I would toss a 6 or 7 amp fuse in the slot for the high speed fan. Get in the car, turn the fan on high wait 60 seconds and see if the fuse is smoked. Did it blow? If it did the problem is from the relay to the fuse block.
Shut the fan off, and toss the relay back in and repeat the check. That 6 or 7 amp fuse should hold no problem. If not the problem is from the relay to the motor plug
If it doesn’t, unplug the resistor block and check it again. If the fuse now holds you have tracked down a problem to the wires from the block to the fan.
Some time in the process I would also check the resistor block plug. Because the resistor block works on the low speeds and the fact that the block is mounted inside a plastic HVAC box, it should not be the culprit.
Check the plugs and wires especially at the motor and the resistor block. Because they are in proximity to the heater box and on the motor those are the ones that go bad first.
If any connector looks smoked…. Replace it. If the motor draws more than 26 amps it is not in the best of shape. You see fusses are not supposed to run at or near the rating. Fuse conduction current close to the rating will blow from minuets to hrs. You can get charts on the expected blow time by checking out the technical specification for fuses on the net. Different sizes and types have different ratings.
There should be two fuses; one that runs everything and the low speeds and that is 25 amps. The high-speed only fuse is 30 amps for the high speed.

when it comes to dealing with the shop.... ask you never know they may or not replace the fan for free..... but they will charge you for finding the bad wires