Why a Heat Pump in Houston Wants Two Visits a Year, Not One

A heat pump is not simply an air conditioner with a heating mode bolted on. It's the same refrigeration loop as a straight AC system, but it runs backward on demand, pulling heat out of the outdoor air in winter and moving it inside, then reversing direction in summer to do the opposite. That reversal is handled by one specific part, the reversing valve, and it's also the part that's doing nothing at all for half the year in either direction. A single annual visit checks whichever mode happens to be running that day and tells you almost nothing about the other one.

What can go wrong in each direction

In cooling mode, a heat pump fails the same ways a standard AC does: weak airflow, refrigerant issues, electrical wear. In heating mode, the failure list is different. Cold air blowing when it should be warm usually means the reversing valve isn't shifting the way it should. A unit that won't switch between heating and cooling at all points to the same valve or its control solenoid. Ice that won't clear off the outdoor coil during a heating cycle means the defrost board isn't triggering the automatic defrost cycle correctly, which is worth knowing before the coldest week of the year, not during it. And auxiliary heat kicking in far more than it should is often the earliest sign that the heat pump side isn't carrying its share of the load anymore.

• Cold air blowing when the thermostat is calling for heat
• The system won't switch between heating and cooling modes
• Ice on the outdoor coil that never fully clears
• The unit running constantly without satisfying the thermostat
• Auxiliary or backup heat engaging more often than it should

What the defrost cycle is actually doing

In heating mode, a heat pump's outdoor coil is doing the opposite of what it does in summer, pulling heat out of the outdoor air even when that air is cold, which naturally causes frost to build up on the coil over time. To clear it, the system briefly reverses itself back into cooling mode for a few minutes, which is why you might glance outside on a cold day and see steam or hear the outdoor fan pause while the unit runs what looks like an air conditioning cycle in the middle of winter. That's normal. It's the defrost board's job to time those cycles correctly, kicking in only when frost has actually built up and running only as long as it takes to clear it.

A defrost board with a failing sensor or a stuck timer either skips defrost cycles it should be running, letting ice build into a solid block on the coil, or runs them too often, which wastes energy and leans harder on backup heat than it needs to. Either failure looks the same to a homeowner: a system that seems to run constantly without the house ever quite reaching temperature.

Why Houston's climate makes this worse than it sounds

Houston doesn't get the deep, sustained cold that forces a heat pump to lean hard on backup heat for weeks at a time, but it does throw short, sharp cold snaps with big overnight temperature drops, right after weeks of nothing but cooling demand. That's an abrupt switch for a machine that's been running one direction almost exclusively. A reversing valve that's stuck from months of disuse, or a defrost board with a marginal sensor, tends to show its problem on exactly that kind of night, the first hard freeze after a long stretch of AC-only weather.

That's the reasoning behind bi-annual heat pump service, once in spring before the cooling season and once in fall before the heating season, with both operating modes actually run and verified at each visit rather than assumed to be fine because the other one worked. It costs one extra visit a year to catch a reversing valve or defrost board problem in April instead of finding out about it in January. If your heat pump is doing any of the things on that list, our technicians run reversing valve and defrost board diagnostics as part of the repair call, and the line is answered any hour if it's gone out on you.