F355 heater (again sorry) and cooling fans

There are known issues and, of course, there are fixes. Some fixes are cheaper than others.

The 30 amp fuse powers most of the HVAC system, so it's a matter of figuring out which component is causing the problem. Likely problems are the blower motor, the power controller for the blower motor or the aircon compressor clutch. These pull the highest currents. Do you already have access to the components in the forward luggage compartment?

Unfortunately, I'm not sure how smart the system is. If you start disconnecting certain components, the ECU might shut down the whole system rather than allowing half the system to operate, but you could try disconnecting the connector on your receiver dryer switches, then resetting your circuit breaker and turning the HVAC system back on to see what happens. Disconnecting this connector will stop your compressor clutch engaging. Note that doing this will also stop your radiator fan operating, so don't leave the engine running for too long. If your circuit breaker remains set and your fan continues to run, then it's likely that your aircon compressor is at fault. If your circuit breaker pops, then most likely it's the blower motor or another component. Note that the radiator fan uses another power source. By the way, what happens if you turn off your blower fan manually using the control panel and reset everything? Does the CB remain set?

You could also try pulling the forward relay of the two HVAC relays (bolted to the right side of the blower fan box). This takes CB/fuse power off everything except the ECU. This might help to isolate the problem to the ECU or the wiring to the ECU.

 

I have a new "917" and two used "917"s and two used "944"s if anyone needs one. I got them a few years ago, after mine went out, for around $200 each.