IMac – Is lowering the ODD fan speed dangerous after installing and SSD

You should certainly request help online or through the phone - (31) 0900 7777 703 - in either Netherlands or the country where your mac was originally sold. Fans are pretty easy to diagnose remotely since it's almost always the fan unit failing (or when it's not that, the next most likely cause is simply reconnecting the fan cable) so you can often ask for a parts and labor quote to help you decide what to do.

You seem to indicate it's the CPU fan. It and the hard drive fan are very hard to replace as you have to disconnect and remove the LCD panel, the logic board and many of the other parts. The optical fan is more amenable to a DIY repair. All the connectors are very delicate and if you break them, the cost to repair can be pretty large. (Think $800 to $1100 for a whole logic board). iFixit.com has good take apart manuals and once you have a quote or two from authorized service providers, you might decide to get inside to reconnect the cables and at least look around.

My advice is don't do anything yourself until you're sure Apple won't cover it by calling them first to get a quote. The main hardware warranty has great links for getting service worldwide - since it's quite long I'll pull the links here for quick reference:

• International Support Information
• Apple Authorized Service Providers
• Apple Retail Store
• Apple Support and Service Phone Contacts Worldwide
• Apple Complimentary Support

Lastly, don't be afraid to run it for short time and low CPU use to get more information and be sure which fan went out. The CPU will reduce clock rate when it gets warm, then it will go to sleep for 30 seconds if that doesn't keep it cool, next the OS will shut down (all of the above events get logged at default settings except maybe the clock rate). The CPU will also shut everything off abruptly if all of the above fail. Don't run for weeks or hit the CPU with 100% tasks and expect it to last for years with the CPU fan off, but other things will have to fail for it to be a melt / fire hazard issue. I also wouldn't run it needlessly and risk MLB failure needlessly.

As you have seen, all Apple products actually run even when you power them off. On iOS, the battery keeps time and on Macs, the SMC is responsible for knowing when the power button is pressed and if the Mac should start itself up due to a scheduled wake or power on being saved in the NVRAM.

If you called for service, Apple would likely focus on several things:

1. Have you checked that the firmware and software is up to date.
2. Does this happen every single time, or is it an occasional thing.
3. Have you disconnected everything (including the mouse and keyboard) and tested to see if it's in any way related to a peripheral.

Assuming you can reproduce this at will (it happens every time), you would probably take steps to reset the SMC to ensure it's getting proper readings from the temperature sensors.

• Intel-based Macs: Resetting the System Management Controller (SMC)

If after spending the 10 minutes it would take to read through each and every step (I feel it's important to perform the steps in order - even if they seem unrelated or unnecessary), I would expect them to want to run diagnostics to physically open the Mac to check the sensors and wiring. Your symptoms sure sounds like the SMC either is stuck in some loop and not reading the temp sensors. Failure to control the fans properly could also be a hardware issue where the SMC is receiving a signal where the correct action is to keep the fans not only spinning, but spinning at an elevated level.