Nine months of cooling, and three that decide whether the system was any good

Two possibilities, and they are easy to tell apart after the event. If the system ran continuously and the house slowly lost ground, it is capacity or backup heat. If it stopped, cycled oddly or blew cool air, it is a fault. The single most common finding after a hard freeze here is a failed electric backup element on a heat pump — it is a separate system inside the same cabinet, it may not have run since last winter, and a failed element does not announce itself. Measuring amp draw on each stage takes five minutes and is skipped constantly. What we would not do is quote a bigger system on the strength of one bad week.

Some frost is, and the machine clears it by itself — steam, a change in noise and a puddle underneath are all part of a normal defrost cycle. What is not normal is ice that never clears, ice filling the base of the unit, or a coil encased solid. The commonest cause is drainage rather than refrigerant: defrost water that cannot get away refreezes into a block under the coil, and from then on the unit cannot defrost at all. If it happens, switch to emergency heat so the house stays warm, and do not chip at it with anything metal — warm water is acceptable, a screwdriver destroys coils.

On a heat pump, the compressor does the efficient heating and the electric elements do the expensive kind. If the system brings the elements in too readily, or if the thermostat has been left on emergency heat, the bill rises by a multiple rather than a percentage with nothing about the house having changed. Three free checks: whether the thermostat is on emergency or auxiliary heat and has been left there, whether large setbacks are being used because recovering from one brings the elements on every morning, and what the balance point is set to. Correcting staging is usually a settings change rather than a purchase.

Rarely, and not before three things have been measured: airflow at every register on both floors, static pressure against the equipment’s rated limit, and return capacity upstairs specifically. In these houses the returns were usually fitted downstairs where they were cheapest, and the attic runs have often sagged or come apart. Adding return capacity upstairs, repairing the attic runs and balancing the system fixes a large share of these complaints for a fraction of a second system. Zoning or a second system is the answer sometimes — but only after the measurements say so.

The heating side, done properly. Every stage of the backup heat operated and its amp draw checked against the nameplate and written down; the balance point and staging settings reviewed; the furnace lit and combustion tested with the heat exchanger inspected if it burns gas; the defrost cycle observed on a heat pump; and the drainage around the outdoor unit checked so meltwater can get away. A great many autumn visits check the cooling equipment and tick the heating, and the failed element that leaves a house cold in February is exactly the thing a tick does not find.

Lewisville, The Colony, Flower Mound, Carrollton, Coppell, Frisco, Highland Village and Castle Hills.