AC tune-up in Purcellville.

Inside the Town of Purcellville close to half the owners heat with electricity, and in a house from the 1990s or 2000s that usually means a heat pump. So the outdoor unit has already worked a full season, pulling heat out of cold air and melting the frost off its own coil. Under a roof edge with no gutter, sliding snow and ice can bend the fan guard and flatten fins along the top. The spring tune-up is the first close look at what that winter left.

The town’s biggest building decade was 2000 to 2009, close to four in ten of its homes. A system that came with one of those houses has 17 to 26 summers behind it, if it hasn’t been swapped already. On an original unit the write-up is the part to keep: how the parts that wear are holding up, and a straight answer on whether to plan for a replacement.

In the old town, the Town’s comprehensive plan describes Victorian houses, bungalows and foursquares, and brick and stone Cape Cods from the 1940s and 50s, all built long before central air. In a Cape Cod the upstairs air handler often sits behind a knee wall beside the bedrooms; in a foursquare, up in the attic. Its drain line takes a long, hidden route out of the house, and clearing it each spring keeps the water out of a plaster ceiling.

Past the town limits, on the farms and the three-to-five-acre lots around town, propane heats close to half the owner homes. In those houses the cooling is a plain air conditioner outside, its coil sitting on the propane furnace indoors, switched off since September. A cabinet beside a field all winter is good shelter for mice and wasps, and their nests can turn up beside the capacitor and the contactor. The tune-up looks in there before the first hot afternoon.