Chosen Solution
After installing a new power supply in my intel imac, the fans are running at very high rpm’s, the noise is very frustrating. Is there a way to slow them down a little ?
Go over all your connections again - pay close attention to sensors. The default for a non-working sensor is to run the fans at max to prevent damage to the CPU. Run AHT in advanced diagnostics 2 or 3X (if you get no error the first run) that may point out which sensor is inoperative. Good Luck, If this Answer is helpful please remember to return and mark it Accepted.
I would download a temperature monitoring application like TG Pro. Then you can isolate which sensor is not working correctly.
I don’t see that AHT error code in the service manual. However the error code ending Tp0P is for the power supply sensor. It says - verify that the single pin connection on the top edge of the power supply is present and securely plugged in. If this sensor wire is not connected correctly the CPU fan will run at full speed. This seems to be a common problem. None of the sensor apps like iStats show the PSU temperature. They show all the other temperature sensors reading normal with the CPU fan speed running over 3000rpm. If this connection is OK in your machine, maybe you new PSU has a bad sensor. There is a single wire connection between the PSU and the temperature sensor boards (at least on my 2007 model). The apple manual says this will cause the fans to run fast if it is disconnected, (or if there is a difference in the PSU). I saw it on mine as a single wire with it’s own plug and socket. It wasn’t the problem with mine. The temperature sensor had fallen off the new HD I installed. What was confusing was the temperature sensor readings looked normal before and after the CPU fan went up to 3000RPM. (Fan control app).
