Mini-Split Not Heating: What Changed

A ductless head that stops heating in winter is often behaving exactly as designed, because defrost cycles interrupt heat delivery on purpose. Telling normal cold-weather operation apart from a genuine fault takes a few specific observations.

EPA 608 Type II CertifiedSafe refrigerant handling

Licensed & Insured$1M general liability

Same-Day ServiceRepairs, tune-ups, installs

Satisfaction GuaranteedWorkmanship you can trust

Defrost Is Designed, Not a Breakdown

The unit reverses periodically to melt frost off the outdoor coil, pausing warm air indoors while vapour and water leave the cabinet. Several minutes about once an hour in damp cold is normal operation.

Reversing Valves Fail Toward the Cooling Side

A valve that no longer shifts completely leaves part of the circuit in cooling while the indoor head is calling for heat. The symptom is steady cold discharge with the compressor audibly running as normal.

Cold-Climate Models Hold Output Further Down

Equipment built for northern winters keeps usable heating capacity at outdoor temperatures where older platforms give up entirely. Which generation is installed decides what January performance is reasonable to expect.

Base Pan Heaters Keep the Drainage Open

Models fitted with a pan heater keep meltwater moving out of the cabinet instead of freezing where it collects. A failed heater lets ice build upward from below until the coil and the fan are locked solid.

Ice That Survives a Defrost Cycle Is a Fault

A coil still encased after the cycle finishes points at a defrost sensor, a valve that will not shift, a low charge, or drainage that refreezes underneath. A coil packed in ice absorbs no heat from the outdoor air.

Heat Pump System Selection Is a Separate Question

Sizing for a Chicago winter, setting a balance point and deciding on backup or dual-fuel arrangements belongs to system planning. What belongs to repair is equipment that heated last winter and stopped.

Steam From the Outdoor Unit Is Usually Defrost

Hot gas sent to the outdoor coil melts accumulated frost and produces visible vapour and running water. The indoor head pauses heat delivery for those minutes, which is designed behaviour rather than a breakdown.

Mounting Height Decides Winter Ice Behaviour

A unit set close to grade drains meltwater into snow that refreezes and builds upward into the coil. Brackets that lift the cabinet clear of accumulation prevent a repeating winter failure.

Reversing Valve Faults Read as Cold Air

A valve that no longer shifts fully leaves the circuit partly in cooling while the head calls for heat. The symptom is steady cold discharge with the compressor running normally.

Rated Heating Output Is Stated at a Temperature

Capacity figures apply at defined outdoor conditions and fall as ambient temperature drops. A room that is comfortable in November and short in January may be meeting the equipment limit rather than a fault.

Winter complaints about ductless equipment split into two groups: the system is doing something normal that looks wrong, and the system has an actual fault. Defrost accounts for a large share of the first group, and knowing what it looks like removes a lot of unnecessary worry.

Defrost Is Not a Failure

In heating mode the outdoor coil runs colder than the air around it, so moisture condenses on it and freezes. Periodically the unit reverses itself, sends hot gas to the outdoor coil and melts that ice off. During those minutes the indoor head stops delivering warm air, the outdoor unit steams, and water runs off the base pan. A cycle lasting several minutes every hour or so in damp cold weather is normal operation. Something that runs for twenty minutes, or repeats every few minutes, is a fault worth investigating.

When the Outdoor Unit Ices Up Properly

Ice that keeps returning after defrost, or that builds into a solid block around the coil and fan, points at a real problem. The usual reasons are a failed defrost sensor, a reversing valve that no longer shifts fully, a low charge, or an outdoor unit mounted where meltwater collects and refreezes underneath. Mounting height matters in Chicago: a unit set close to grade sits in accumulated snow, drains into it and builds ice from below.

Faults That Present as No Heat

Reversing valve stuck in cooling, giving cold air with the compressor running.
Discharge or coil thermistor drift, causing the board to end heating calls early or refuse them.
Outdoor fan failure, which lets the coil ice over within a single cycle in damp weather.
Low refrigerant charge, which shows as heating that works acceptably in mild conditions and then falls away as the outdoor temperature drops through the twenties.
Base pan heater failure on models fitted with one, allowing meltwater to freeze in the pan and block drainage.

Capacity Is Supposed to Fall With Temperature

Heat pumps move heat from outdoor air, and there is less of it available at 5 °F than at 40 °F. Published heating capacity is stated at specific outdoor conditions, and cold-climate models hold usable output much further down than older equipment. A head that heats a room comfortably in November and struggles in January is often working correctly and simply reaching the limit of what the equipment and the room load allow.

Where the Heating Question Actually Belongs

What belongs here is a ductless system that has stopped doing what it did last winter. Choosing a heat pump as the heating system for a house, sizing it for a Chicago winter, setting a balance point and deciding on backup or dual-fuel arrangements is a different question with different inputs, and it starts from the residential heating section. Repairs to the ductless equipment itself stay with mini-split repair and maintenance, and adding zones or replacing the system is ductless installation work.

Snow Drifting Against a Ground-Mounted Cabinet

A unit set low collects drifted snow around the coil, and meltwater from defrost refreezes underneath it. Raising the equipment on brackets removes a failure that repeats every winter otherwise.

Backup Heat Sources in the Same Room

Where a space also has a radiator or an electric heater, a heat pump complaint can turn out to be a control conflict between two systems. Establishing what else heats the room comes early in the visit.

Defrost Records Show the Real Interval

Service data on most platforms logs how often defrost ran and how long each cycle took. Those figures separate normal damp-weather behaviour from a sensor or valve that is not doing its job.

Documenting a Winter Fault for Spring

A heating complaint diagnosed in January often needs a component ordered against the model. Recording the code, the line temperatures and the valve test result keeps the return visit short.

Winter Ductless Heating Questions in Chicago

How long should a defrost cycle last on a ductless system?

Several minutes, repeating roughly once an hour in damp cold weather, with visible vapour and water running from the outdoor unit. The indoor head pauses warm air during that time. Cycles running much longer, or repeating every few minutes, indicate a defrost sensor, valve or charge problem worth investigating.

Why does the outdoor unit build a solid block of ice?

Ice that survives defrost points at a failed defrost sensor, a reversing valve that no longer shifts fully, low refrigerant, or drainage that refreezes under the unit. Mounting height contributes in snow country. A coil encased in ice cannot absorb heat and the system loses heating capacity entirely.

Is reduced heating output in January always a fault?

Heat pumps collect heat from outdoor air, and available heat falls as temperature drops, so rated output is published at stated conditions. Cold-climate models hold usable capacity much further down than older equipment. A head that keeps up in November and struggles in a deep cold snap may be at its designed limit.

What does steady cold air from the head with the compressor running mean?

The circuit is likely still in cooling because the reversing valve has not shifted, or a sensor is reporting a condition that keeps the system out of heating. Both produce cold discharge during a heat call. The stored fault code usually names the circuit, and the valve is tested electrically and by line temperature.

Does this cover choosing a heat pump as the main heating system?

No. Sizing a heat pump for a Chicago winter, setting a balance point and deciding on backup or dual-fuel arrangements is a system-selection question handled in the heating section. What belongs here is a ductless system that heated last winter and has stopped behaving the way it did.