Might have members on more than one Volvo forum...this has been posted to one other site:

Ok, new member here but not new to Volvo's.

Question:

My XC70 had little to no heat in a recent cold spell here in the south. Did some reading and research and one of the common issues is a plugged heater core, however, I found a temporary trick of flushing the core to ensure flow. Well, I did that today and made sure Volvo coolant and distilled water was filled back into the heater core when complete. I saw excellent flow. Following that, we are getting more heat sporadically but if I turn on the A/C compressor, it goes cold even when one or both sides of the dual climate control are full heat. Without the compressor and with the recirculate on, we can get lukewarm at this point with occasional waves of warmer air here and there.

When I pulled back into the driveway, I turned the blower down to the lowest setting so things were quiet and I can hear a whirring back and forth at about the speed of wiper blades: "whir...whir.......whir...whir". So, I turned everything to full cold (no compressor) and I can hear a longer whirring and then silence. Turn it back to full heat and you get a long whir and then the whir...whir again. Seems like maybe a blend door motor may be having an issue?

I'd appreciate any thoughts on this. Given the dual controls, are there more than one servos for this? Should I be testing something else? I've seen some suggestions that the thermostat could also be in play here but not sure how to verify that.

Thanks!
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