My daughter's home from the east coast on winter break. I don't get to see her car but once or twice a year. But she has a indy mechanic that is Volvo only, so it's in good hands, I think.

Her shop, nor my local boys, can seem to solve this wacky climate control.

It has the classic symptoms of the blower motor running fine upon start up for a few minutes, then it goes nuts running on various speeds of its own accord, sometimes with just momentary "puffs" of high speed, only to ultimately quit completely in about 10 minutes. This problem is fairly well documented as being a faulty resistor overheating and shutting down the system. The resistor has been replaced with new OEM at least twice, and I've even soldered in my own transistor from The Shack with no change in behavior. (Why this is called a "resistor" escapes me as the wiring diagram clearly shows two transistors in the component.)

So I'm hesitant to throw another new resistor in there.

Mechanic suggested it might be the blower motor. I can put 12V on the motor directly and it runs like a champ, so I'm thinking it's fine.

Now a new twist: temperature control. On a test drive when the blower was working, the temp was set to Max and the heat came on quite nicely. And it continued to heat, and heat, despite rolling the control back to Min. Only several minutes later (just before the blower quit) did the outside air come through unwarmed. My daughter says that is also very typical behavior for this car.

Now that it has this fan speed control problem, and apparently a temp control issue, does this conclusively point at the CCU (head unit) as the culprit? These are pretty easy to find in salvage yards, assuming they're good.

I'm at the end of my rope with this one. I have about 10 days to solve it before she heads back, 900 miles from here. Not the time of year for unreliable HVAC.

All suggestions are welcome!

Doug in STL
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'94 945t; '94 944t; '05 S80 2.5t; '01 S40t