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Normal hot air from the startup cycle does not bother the AMM, but continued hot air from the manifold after the engine is warmed up will cause the AMM to fail eventually - how long it takes probably depends on a number of factors. Some seem to have hot wire failures, while others seem to have failures in the electronics. Also - engines are designed to operate in a given temperature range. THe thermostatic damper helps the engine to reach this temperature more quickly - thus better lubrication and quicker heat inside the cabin. So it affects both engine wear and driver comfort. Although many will defeat the start-up air feature to avoid a small cost, I recommend that you simply replace the thermostat/damper as required and keep all of the engine features. And, yes, as noted here it is an emissions consideration. BTW - not all cars are equipped with these. The later Volvos - at least some of them - do not have the pre-heat feature.