When a heat pump refuses to warm the house on a chilly morning, frustration lands fast. The thermostat reads “heat,” the air handler hums, yet the vents deliver lukewarm air or nothing at all. Some homeowners jump straight to “furnace not heating,” even though a heat pump isn’t a furnace at all. Others assume the compressor failed. In many cases, neither is true. Heat pumps are particular about airflow, refrigerant charge, and defrost timing. A small imbalance can snowball into a “heater not working” call.
I’ve serviced heat pumps in damp coastal climates, high desert plateaus, and Midwest cul-de-sacs where freezing rain can glaze an outdoor coil in an hour. The patterns repeat. A clump of packed leaves blocks the return. A thermostat mode got toggled to “cool” after an app update. A defrost control board is slow to respond. Before ordering parts, it pays to understand how heat pumps make heat, how they shed frost, and how to balance the system so it doesn’t fight itself.
What a heat pump is actually doing on a cold day
A split-system heat pump squeezes heat out of outdoor air, even when it feels bitter. Refrigerant absorbs heat at the outdoor coil, the compressor raises its temperature and pressure, and the indoor coil releases that heat into your home. When outdoor temperatures drop, a clean coil and strong airflow matter more, because the refrigerant must gather smaller amounts of heat from colder, often wetter air.
The outdoor coil runs colder than the air around it, so moisture freezes on the fins whenever conditions line up. A thin rime is normal. Heavy frost that spreads and stays hour after hour points to a defrost problem or an airflow problem. When frost thickens, heat transfer plummets and the unit may limp along, pulling high amps and giving you room air that feels barely warm.
Contrast that with a gas furnace. If a furnace isn’t heating, you chase different suspects: flame sensor, pressure switch, inducer, gas supply, or high-limit trips. With a heat pump, you start with thermodynamics and airflow, then move to sensors, defrost timing, and refrigerant.
Signs you’re dealing with defrost or balance trouble
Patterns tell the story. If the system heats fine for twenty minutes, then weakens and blows cool air, the outdoor coil may be frosting faster than the defrost cycle can clear it. If the system runs and runs without tripping the thermostat setpoint, yet your kilowatt hours spike this month, the auxiliary heat strips may be carrying the load too often because the heat pump section is underperforming. If the air is warm at first in the morning, then flat by midday, look at return air filters, matted with drywall dust or pet hair, starving the air handler. And if the outdoor unit makes a whooshing sound and switches briefly to air conditioner mode in winter, that is a normal defrost event, not a failure, so long as it is brief and the steam cloud dissipates.
I often ask homeowners three simple questions: Did the outdoor unit look like a snowball during the cold snap? Did you recently change a smart thermostat or a filter? And does the electric bill show a sudden jump compared to similarly cold days last year? Those answers narrow the field.
How defrost cycles work, and how they fail
A modern heat pump uses a control strategy to periodically reverse itself and melt ice from the outdoor coil. The outdoor fan stops, the unit briefly goes into cool mode, and hot refrigerant floods the outdoor coil. Steam rises. After a minute or several, the board returns the unit to heating, and the fan switches back on. Some systems rely on timers plus temperature sensors. Others use demand defrost, measuring coil temperature and ambient to decide when to act. Either way, the goal is to clear frost without wasting energy.
Failure shows up in a few ways. The coil frosts quickly but the board never commands a defrost, usually due to a failed sensor, bad wiring, or corroded connectors. The board initiates defrost, yet the reversing valve doesn’t shift because the solenoid is stuck or the valve body is worn. Or the system defrosts, but can’t keep up because the outdoor fan motor is weak, the blades are damaged, or airflow through the coil is obstructed by debris and snow.
A less common but tricky scenario occurs when the system defrosts too often. If the coil sensor reads colder than reality due to poor contact or a misplaced clip, the unit can spend an excessive amount of time in defrost. Each event uses energy and interrupts heating, which feels like a heater not working even though the machine is technically functional.
Quick checks you can do before calling a tech
You can learn a surprising amount without tools. Look at the outdoor unit during a heating call. If the coil is evenly frosted but not encased and the fan is spinning, https://fernandojrkm028.timeforchangecounselling.com/ac-not-cooling-after-refrigerant-recharge-what-went-wrong that may be normal in damp air just before a defrost. If the coil is buried in ice, with the fan still trying, kill power at the disconnect and gently clear away drifted snow or leaves around the base and sides. Do not chip at the fins. Once airflow is restored around the cabinet, restore power and watch for a defrost event within the hour.
Feel the supply air at a main vent. It should be warmer than the room. In milder weather, heat pumps blow air in the 85 to 95 F range, which can feel less warm than furnace air but is still heating. If it feels room temperature or cooler for more than a few minutes, something is off. Check the filter. If it’s loaded, swap it. A clogged filter is the cheapest, most common cause of poor heating and short equipment life on these systems.
Check the thermostat mode and setpoint. Heat pumps with dual-fuel or auxiliary heat stages can lock out the compressor below a certain outdoor temperature if settings are wrong. A new Wi-Fi thermostat sometimes defaults to generic heat mode instead of heat pump mode, which confuses staging and defrost logic.
Finally, look at your breaker panel. Many air handlers with electric heat strips have two breakers: one for the blower and controls, another for heat strips. A tripped strip breaker means the heat pump may struggle to maintain temperature during defrost events or very cold nights. Reset once. If it trips again, you need a technician to diagnose why.
Balancing airflow: the unglamorous fix that saves systems
Most heat pump complaints trace back to airflow. The equipment was sized correctly, the refrigerant charge was fine last spring, yet winter performance is poor because the duct system chokes it. Heat pumps move large volumes of air at lower temperature rises than furnaces, so they are sensitive to duct restriction. I’ve seen beautifully installed outdoor units paired with return ducts that would suit a toaster oven. The static pressure pins the blower to its limit, noise climbs, and the coil runs colder than designed. Frost accelerates, defrost runs more often, energy use climbs, and comfort drops.
Balancing starts with the basics: clear returns and open supply registers. Furniture pressed tight against the only return in a room can slash airflow. Closing too many bedroom registers in the hope of pushing heat to the living room often backfires, driving up static pressure and bypass leakage, and causing the coil to run too cold. Ducts in attics or crawlspaces leak at joints and boots. Fifty cubic feet per minute missing at the return can be the difference between a steady, comfortable heat pump and an ice maker.
When I balance a system, I measure external static pressure, compare it to the blower’s rated performance, and adjust tap settings or ECM profiles to hit the design airflow. I also confirm that the filter rack isn’t undersized. A 20 by 20 filter on a three-ton system may be marginal. Upsizing to a deeper media cabinet reduces pressure drop and lengthens filter life. These changes may sound boring, but they extend hvac system lifespan and reduce nuisance frost.
Defrost timing adjustments and when to touch them
Technicians sometimes tweak defrost intervals on timer-based boards to match local climate. In wet, near-freezing weather, a shorter interval may keep the coil cleaner. In colder, drier air, frost builds slowly and longer intervals save energy. Homeowners rarely need to touch these settings. If your board has a selector that toggles between 30, 60, and 90 minutes, the right choice depends on your region and equipment condition. Blindly switching to the shortest interval makes the unit defrost more often, which can mask underlying airflow issues for a few days while increasing energy use.
Demand defrost systems rely on temperature sensors at the coil. If these sensors lose good thermal contact due to corrosion or loose clips, the board reads wrong. That’s a repair job, not a settings job. The most productive “adjustment” a homeowner can make is clearing vegetation to a two-foot radius around the unit and maintaining a firm, level pad so melted frost drains away instead of refreezing at the base.
Auxiliary heat, balance points, and energy bills
Heat pumps often have a “balance point,” the outdoor temperature at which the compressor alone cannot meet demand. Below that point, electric resistance strips or a gas furnace in dual-fuel setups takes over. If your system uses strips, any prolonged defrost relies on those strips to temper indoor air while the outdoor coil melts. If the strip breaker is tripped or the strips are failed, each defrost feels like a blast of cool air and the house loses ground. If the strips work but engage too often, your bill spikes.
On many thermostats, you can limit how aggressively auxiliary heat kicks in. If you set a small maximum temperature rise per hour or lengthen the delay before calling strips, the compressor does more of the work. This helps in milder climates where a patient compressor can catch up. In harsher climates, overly strict limits cause long runtimes and discomfort. Field experience matters here. In the Mid-Atlantic, I tune aux heat to engage only if the setpoint is more than two degrees away for a certain time. In northern Minnesota, this approach can make people miserable. The right strategy depends on your home’s heat loss, duct performance, and the equipment’s capacity curve.
Why “AC not cooling” visits often reveal a heat pump problem
When spring arrives, I get calls about ac not cooling, and the culprit turns out to be the very same frosting and airflow issues that bugged the system in winter. A heat pump that struggled to defrost efficiently likely had a dirty outdoor coil and mangled fins. In summer, the same coil can’t reject heat well in cooling mode. The system runs high head pressure, trips on safety, or delivers weak cooling. The owner remembers a winter episode of “heater not working,” but never connected the dots. The lesson is simple: treat both seasons as the same machine with two sets of stresses. Good maintenance habits carry across.
Filter strategy and return placement, with real numbers
Filters look simple, yet choosing the right media and area matters. Aim for a face velocity at the filter of roughly 300 to 400 feet per minute for common pleated media, lower if you want quieter operation and longer life. For a three-ton heat pump moving around 1,100 to 1,200 cubic feet per minute, a single 20 by 20 filter runs at 330 to 360 feet per minute, which is acceptable but leaves little headroom once it starts loading. A 20 by 25 brings that down into the comfortable range. A deeper 4 or 5 inch media cabinet further reduces pressure drop.
Return location is equally important. If your only return is in a hallway ceiling, rooms with closed doors can starve. Undercut doors help, but jumper ducts or transfer grilles work better. On cold nights, poor return path restricts flow and the indoor coil runs colder than intended. That translates directly into more frost outside.
Refrigerant charge and the pitfalls of topping off
Heat pumps rely on precise refrigerant mass to hit target pressures and superheat/subcooling. A small undercharge reduces capacity and increases frosting. An overcharge can flood the coil, wash oil out of the compressor, and create its own performance issues. I’ve revisited systems where a well-meaning tech added a pound in January based on “it looked low,” only to find in April that the unit short-cycles and the suction line sweats excessively. Charging in cold weather is tricky without proper tools and methods, like weighing in or using manufacturer cold-weather charging charts. Homeowners should be wary of annual top-offs as a ritual. Refrigerant isn’t a consumable. If it is low, it leaked. Find the leak or you will buy the same pound twice a year while quietly shortening equipment life.
Balancing a multi-zone heat pump without confusing it
Ducted heat pumps tied to zone dampers can be comfortable and efficient, but the control logic must keep minimum airflow across the coil. If one small bedroom calls alone and the system doesn’t open a bypass or a second zone to share, the coil may run cold, the compressor short-cycles, and frost forms faster. The fix is to set minimum open percentages on dampers, program priority rules, and ensure a pressure relief strategy that doesn’t waste energy. Bypass ducts to the return are falling out of favor because they waste cooling or heating by mixing supply with return, but a controlled, limited bypass or a designated “dump” zone can prevent coil starvation.
Zoned systems that misbehave often create confusing symptoms: rooms overshoot, then undershoot, and the owner reports both furnace not heating and ac not cooling within the same season. The root is usually control strategy, not hardware failure.
What maintenance actually pays off for heat pumps
A solid maintenance routine can be summed up in a few targeted actions. Clean the outdoor coil with low-pressure water from the inside out after pollen season, not with a power washer that folds fins. Keep shrubs trimmed at least two feet away. Level the condenser pad and restore proper drainage if winter heave or mulch has trapped water around the base. Change filters on time, using deeper media where possible to reduce static. Inspect and seal accessible duct leaks with mastic, especially at the return plenum and filter rack where the system can suck in attic dust.
During a professional tune-up, ask for real measurements: static pressure, temperature rise, superheat and subcooling as appropriate, and a defrost control check. Numbers beat impressions. A report that lists “checked OK” without data tells you little. Over time, you will see trends. A slow climb in static pressure indicates duct or filter issues. A drift in subcooling can flag a slow leak early. This approach extends hvac system lifespan more reliably than any fancy accessory.
When behavior is normal, and when to worry
Heat pumps don’t blow hot air like furnaces at all times. On mild days, the supply temperature can feel lukewarm to your hand yet still be adding heat steadily. Short defrost cycles that occur a few times on a wet, 34 F day are expected. Outdoor units making a brief whoosh followed by visible vapor is steam, not smoke. That said, there are red flags. A coil encased in thick ice after hours of operation is not normal. Frequent defrosts that last long enough to make rooms feel cooler each time aren’t normal. A breaker that trips more than once, a burning smell, or a compressor that hums and kicks off requires a technician.
Trust your senses and the calendar. If performance degrades suddenly after a storm or a landscaping project, suspect airflow and damage. If it creeps over weeks, look for filter loading or a sensor issue. If the system has always struggled below a certain temperature, revisit balance point settings, duct capacity, or equipment sizing.
Choosing settings that help more than they hurt
Thermostat settings shape how your heat pump behaves through the seasons. Avoid constant swings of several degrees. Heat pumps prefer steady-state operation. If you like overnight setbacks, keep them modest. A three-degree setback may be fine in a well-insulated home. A ten-degree setback often triggers long recovery times and heavy auxiliary heat, wiping out any savings.
Fan mode should stay on “auto” most of the time. Running the fan “on” constantly can re-evaporate moisture in cooling season and push cool-feeling air in heating when the coil is off. In shoulder seasons, constant fan can help blend room temperatures, but watch comfort.
If your thermostat allows outdoor temperature awareness, set reasonable lockouts. In dual-fuel systems, decide at what outdoor temperature the gas furnace should take over. In all-electric systems, set a balance between comfort and energy by choosing when to allow strips and how quickly. Get to know your equipment’s behavior and adjust in small increments, not big swings.
A realistic path from “heater not working” to steady comfort
The fastest path starts with basics: verify mode and setpoint, inspect filters, and walk around the outdoor unit for airflow obstructions and ice. Watch or listen for a defrost event. If problems persist, look for patterns: time of day, weather, and whether auxiliary heat is engaging. If you call a professional, be ready to share those observations. Ask for measured data and a plain explanation. A good technician will talk about airflow and defrost control before swapping parts.
Most heat pump heating complaints resolve without replacing the compressor. The culprits are more humble: a neglected filter, matted coil fins, a return grille behind a couch, a misconfigured thermostat, a tripped strip breaker, a sagging duct or a loose coil sensor. Addressing these keeps both your winter heating and summer cooling on track and avoids the ping-pong of ac not cooling and furnace not heating calls that drain budgets and patience.
Heat pumps reward balance. Keep air moving freely, give the defrost system the information it needs, use auxiliary heat wisely, and the system will do quiet, steady work year after year. That steadiness is not just comfortable. It is the simplest way to protect performance, lower utility costs, and stretch hvac system lifespan without drama or guesswork.
AirPro Heating & Cooling
Address: 102 Park Central Ct, Nicholasville, KY 40356
Phone: (859) 549-7341