Heat Pump Not Cooling in Summer? What to Check
Heat pumps are everywhere in the D.C. area's townhomes and condos, and in summer they are simply air conditioners running in one direction. That means most cooling failures follow the standard AC script, which our AC troubleshooting guide covers check by check: thermostat mode and fan setting, a clean filter, an unfrozen indoor coil, breakers, and an outdoor unit whose fan actually spins on a clear coil. Run that list first. This guide covers what is different when the machine is a heat pump.
The failure unique to heat pumps: the reversing valve
A heat pump chooses between heating and cooling with a reversing valve. When that valve or its solenoid sticks, you get the signature heat pump complaint: the system runs, and the vents blow air that is warm, or even heated, while the thermostat calls for cooling. If your "not cooling" is actually "gently heating," stop troubleshooting airflow; this is the valve, and it is professional territory involving the sealed refrigerant circuit. The good news is that the symptom is so distinctive that diagnosis is usually quick.
Thermostat wiring quirks: the O/B setting
Heat pump thermostats energize the reversing valve through an O/B wire, and the thermostat must be configured for the correct convention. After a DIY smart-thermostat installation, a wrong O/B setting produces cooling when heat is called and vice versa, a perfect imitation of a failed valve. If the problems began the week a new thermostat went in, revisit its heat pump configuration before assuming hardware failed.
What "working" should feel like
Heat pumps cool by the same physics as any AC and deliver a similar result: air from the supply vents should measure roughly 15 to 20 degrees cooler than the air returning at the filter grille. Measure both with a simple thermometer. A healthy split with a warm house points at runtime, sizing, duct losses or extreme heat load, not the equipment. A weak split points back at airflow, a dirty outdoor coil or refrigerant charge.
Ice on the outdoor unit in July
Frost or ice on the outdoor unit or refrigerant lines in summer is never normal. It signals starved airflow or low refrigerant, and running the system while iced risks the compressor. Shut cooling off, let it thaw, replace the filter, and if ice returns, book service; a refrigerant leak needs finding and fixing, not topping off.
Age, capacity and honest expectations
A heat pump that cools adequately at 85°F but loses ground at 95°F may be undersized, aging, or fighting duct leaks in a hot attic rather than broken. A technician can distinguish a failing system from an outmatched one with pressure and temperature measurements, and that distinction is exactly what should shape any repair-versus-replace conversation, especially on units past their twelfth summer.
When to book
Call for service when the system heats on a call for cooling, when ice appears, when breakers retrip, or when the temperature split stays weak after the basic checks. Appliance Surgeon repairs heat pumps and all HVAC systems across the metro area, including Lorton and Colchester. Book ahead of the forecast; reversing-valve work in the first heat wave competes with every capacitor in the region.
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