Volvo Repair: ECC Fault - Random Fan Failure, loud roar, fan failure

Question
I've been experiencing a strange and random fault in my interior heat/AC fan. On occasion (and there is no commonality to hot/cold, rain/dry or other occurance that I can find) the fan for the heater/AC will not work. Here's the scenairo:
1) Get in the car and start engine
2) Fan comes on with an unusually loud roar for about 2 seconds
3) Fan stops
4) Lights on AC Off and Air Recycle buttons (orange) flash on and off for about 20 seconds.
5) Fan is now inoperable in any postion

This only happens when the car is first started. If the fan does work it has never stopped while the car is running. If I turn off the engine and restart it, the fan may work or it may repeat the sequence above. It's random. Sometimes I can go for a week or two without it happening other times it might do this for a week or two and then start up again.

I'm trying to get a list of all the things that this could be. I did note that the interior temp sensor was replaced when the car was under warrenty and it DID NOT fix the issue. Here's what I think might be involved
1) Resistor
2) Temp sensor (but not likely as replaced already and didn't fix)
3) Fan motor
4) The small air intake fan used to bring air to the temp sensor
5) Relay (I have heard that there is no heater/AC relay in the 1999 XC..can you confirm that?)
6) Wires or connectors
7) Control Unit (dash control unit)

My indy mechanic replaced the resistor and it still didn't work so that one seems out. He also took a control unit out of another XC and replaced and it still didn't work. So that appears to be out. He said there was not Heater/AC relay in the 99 XC so if he's right that's out. I'm down to the fan motor or wires and connectors or maybe a bad temp sensor when it was replaced.

Can you provide some insight into this problem?
Thanks,
Tom


Answer
2 common causes for this type problem the fan powerstage (aka resistor) is bad or the motor start up current is excessive intermitently and causes the fan to shut off.since the resistor was changed I would think the motor is bad.you should be able to get a code from the a/c syatem with a scan tool.