A heat pump is one machine doing two jobs a furnace-and-AC setup splits between two machines. That's the whole reason heat pump troubleshooting trips people up. The same outdoor unit that cools your house in July has to reverse itself and pull heat from outside air in January, using a reversing valve and a defrost cycle a plain AC doesn't have. Most of the confusing symptoms below trace back to that one difference.
Why heat pumps act differently than a furnace-and-AC system
A furnace burns gas or runs electric elements to make heat that's clearly hotter than your skin. A heat pump in heating mode delivers air around 85-95°F. That's below your body temperature of 98.6°F, so it feels cool on your hand even when the system is running exactly as designed. This single fact explains more "my heat pump isn't working" calls than any actual failure. Before you assume something's broken, check a supply vent with a thermometer, not your palm.
The second big difference is the defrost cycle. In cold, damp weather the outdoor coil ices up, and the system periodically reverses to melt it off. Steam rising off the outdoor unit, a whooshing sound, and a few minutes of cooler indoor air are normal during defrost, not a malfunction. Auxiliary heat usually kicks in during defrost to keep the house comfortable while the compressor is busy melting ice instead of heating.
Arizona adds its own wrinkle. Winters here are mild, so heat pumps spend most of their working life in cooling mode and only light duty in heating mode. Defrost and emergency-heat problems that plague a heat pump in Denver or Chicago show up far less here, and a unit that struggles on a rare 28°F Phoenix night is a different animal than one straining through a Minnesota winter. Keep that context in mind as you read the guides below.
Not heating
- Heat pump not heating - the system runs but the house stays cold, or heat output feels weak.
- Heat pump blowing cold air - air feels cool to the touch even in heat mode. Read this one first if that's your complaint; it's usually not what it seems.
- Heat pump not turning on - no fan, no compressor, nothing happening at all.
- Heat pump emergency heat - what EM heat mode actually does, how it differs from auxiliary heat, and when you should and shouldn't use it.
Noise and behavior
- Heat pump running constantly - the system never shuts off, or cycles on and off in short bursts.
- Heat pump defrost cycle - what a normal defrost cycle looks and sounds like, and how to tell it apart from a real fault.
Ice and freezing
- Heat pump frozen - ice on the outdoor unit that doesn't clear on its own, or a solid block of ice encasing the coil.
Costs and repair
- Heat pump repair - common failures, typical repair costs, and the math on repairing versus replacing.
- Heat pump installation cost - what a new system runs and what drives the price up or down.
- Heat pump not cooling - the cooling-side version of these problems, since Arizona heat pumps spend most of the year in AC mode.
Safe checks vs. call-a-pro symptoms
A handful of checks are safe for almost any homeowner: thermostat batteries and mode setting, breakers, the disconnect box next to the outdoor unit, and the air filter. Do those first, every time, before anything else.
Past that line, stop touching things. A reversing valve, a defrost control board, and anything inside the refrigerant circuit require licensed hands and, for refrigerant work specifically, EPA Section 608 certification under federal law. You can read the underlying rule on the EPA's Section 608 program page. If a symptom points toward one of those components, the guide for that symptom will tell you plainly, and the next step is a phone call rather than a screwdriver.
Common questions
What's the difference between a heat pump and a regular AC when something goes wrong?
An AC only moves heat one direction: outside. A heat pump reverses that flow using a reversing valve, so it can fail in ways a plain AC can't, like getting stuck in the wrong mode or running a defrost cycle that never completes. Diagnosing a heat pump means checking components an AC diagnostic skips.
Why does my heat pump blow air that feels cold in heat mode?
Heating-mode air runs 85-95°F, which is below your 98.6°F body temperature. It feels cool on your hand even when the system works fine. If the air is truly room-temperature or colder, or the house isn't warming up over time, that's when to suspect a real problem like a stuck reversing valve.
Is it normal for my heat pump to ice over in winter?
Some frost during a scheduled defrost cycle is normal and clears within 10-15 minutes as the unit reverses and melts it off. Ice that never clears, or a solid block encasing the whole outdoor unit, points to a stuck reversing valve or failed defrost board. See heat pump frozen for the full breakdown.
Do Arizona heat pumps have fewer winter problems than heat pumps elsewhere?
Generally yes. Arizona winters are mild, so heat pumps here run heavily in cooling mode and see comparatively light duty in heating mode. Defrost cycling and emergency-heat situations that are routine in colder states are rarer here, though a cold snap can still expose an aging or undersized system.
My symptom doesn't match anything on this page. What now?
Start with heat pump repair for what the fixes actually cost, or use the quote form below to get a licensed technician out to diagnose it directly. Guessing at refrigerant-circuit repairs tends to cost more than a diagnostic visit.
Get matched with a licensed technician
If you've worked through the checks above and the system still isn't right, use the quote form below to compare licensed heat pump contractors near you, including options in Phoenix, Mesa, and Chandler. Look up any contractor's license at azroc.gov before they show up.