I don't know anyone who can read out Volvo-specific diagnostic codes from the dual ECC. As the weather has been growing warmer, the passenger side is stuck on full heat, and I have been dreading the spring weather, even with the "oreos" (vent wheels) closed on the passenger side. The driver's side is just blowing ambient air -- no real AC.

The car was due for 97K service, so I took it to the dealer, but I've been thinking recently, what if the problem is the voltage level? I have a 5 year old battery, and the starter motor has been slow-cranking the past 6 months, tho it starts the car after a couple of seconds.

So before checking in for service at the dealer, I bought a new battery. There was an immediate effect.
The word "miracle" describes what happened. The heat / AC is back to normal on both sides!

The lesson here is about microcontrollers. During starter cranking, the battery is pulled down to its lowest voltage, while at the same time all the little on-board computers are getting booted. Clearly, by letting my battery age too far, the ECC subsystem was undervoltaged during their bootup sequence. This explains why my ECC has been acting flaky the past 6 months, assuming different aberrant personalities that could change by restarting the engine.

This episode points out the electrical voltage during starter cranking has to remain in the range-of-operation demanded by the computers, 13.5 to 14.3 volts DC. When control systems are misbehaving, the first thing to check is for voltage malnourishment.