Emergency HVAC → Cooling
All three look identical at the vent. The outdoor unit separates them in about thirty seconds, and that one observation decides what the repair costs.
An AC blowing hot air is still moving air but no longer removing heat from it. Three causes account for almost every case: a frozen evaporator coil, a failed run capacitor that costs under $30 as a part and $200 to $300 fitted, or a refrigerant charge that has leaked away.
None of them can be told apart at the vent, which is why diagnosing an AC blowing hot air starts outside rather than indoors.
Thirty-second split
Everything you need to narrow this down is out there. Listen and look before you touch anything indoors.
Neither the fan nor the compressor is running while the indoor fan is. That points at a failed run capacitor or a contactor, and it is the most common sudden failure.
A hum without a start is the classic capacitor signature. Switch the system off rather than leave it straining.
The system is trying and not achieving, which points at refrigerant charge, a frozen indoor coil, or airflow. Go back inside and look for ice.
Not one page ranking for this search uses that split, and it is the single most efficient diagnostic available to a homeowner. It costs nothing, needs no tools, and it determines which of the three causes below you are dealing with.
The indoor coil gets cold in order to condense moisture out of the air. If airflow across it drops, it gets colder still, the condensate freezes, and the ice then blocks airflow further.
That feedback loop is why a slightly dirty filter becomes a completely frozen coil over a few hours. The end state is a system running flat out and delivering room-temperature air, because almost nothing is getting through the ice.
This is the most common sudden failure in residential air conditioning and the single most argued-about line on an HVAC invoice.
The run capacitor gives the compressor and outdoor fan motor the phase shift they need to start. When it weakens, the indoor fan keeps running normally while the outdoor unit either sits silent or hums without starting, so air keeps coming out of the vents and it is simply not cold.
The part costs under $30. Fitted, the job commonly runs $200 to $300 in standard hours and considerably more after them, which is a real source of homeowner frustration and also a real reflection of a stocked van, a licence and an out-of-hours rota.
Capacitors hold a charge after the power is off
This is the reason capacitor replacement is not a homeowner job even though the part is cheap and the swap looks trivial. A run capacitor stores enough energy to injure you after the disconnect is pulled, and it has to be discharged deliberately before anything is touched. Every video that skips that step is teaching people to take a shock.
Does an AC need refrigerant topping up?
No. Refrigerant circulates in a sealed system and is not consumed. If the charge is low, it escaped through a leak, and it will escape again. A recharge without a leak repair buys a season at best.
This is the point where the industry and the customer most often talk past each other. A recharge is a legitimate short-term measure, particularly in the middle of a heatwave, and it is not a repair.
Ask for the leak search and the repair quote alongside the recharge price rather than instead of it. If the answer is that the leak is in the evaporator coil or the compressor, that is a genuine repair-or-replace conversation on any system over about ten years old.
There is no home test, and any page implying otherwise is wrong. There are three signs worth reporting to a technician.
Confirming it needs manifold gauges, and in the United States handling refrigerant requires EPA certification. Venting it deliberately is a federal offence, which is why the DIY canisters sold for cars have no equivalent for home systems.
An AC blowing hot air should be switched off in every case except a frozen coil.
A system that cannot remove heat is achieving nothing while wearing components and consuming electricity. If the compressor is humming without starting, running it is actively damaging. Switch it off at the thermostat and leave it off until someone looks at it.
The exception matters though. With ice present, switch to fan only rather than off, because the moving air is what thaws the coil. Turning the system fully off leaves the ice in place for far longer. Our page on an AC that will not start at all covers the reset sequence if nothing runs.
A large share of searches for this phrase are about vehicles. If yours is a car, the components and the refrigerant are different and this is a job for a mechanic rather than an HVAC contractor.
Window and portable units share the logic on this page. They have capacitors and coils that freeze for the same reasons, and the reset is unplugging the unit for five minutes rather than a breaker sequence.
Know the line
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Tell us what the outdoor unit is doing and give us your ZIP code. Licensed, insured HVAC contractors covering your area will contact you directly. No obligation to hire.
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Indicative US ranges. Always get a written quote.
| Job | Typical range | Notes |
|---|---|---|
| Run capacitor replacement | $200–$300 | Standard hours; the part itself is under $30 |
| Refrigerant recharge | $250–$600 | Temporary unless the leak is also repaired |
| Blower motor | $400–$900 | Standard hours |
| After-hours diagnostic fee | $150–$250 | $225–$500 on a holiday |
| Emergency labor multiplier | 1.5×–3× | Applied to the standard hourly rate |
Source: 2026 emergency HVAC rate aggregator data; HomeGuide 2026 HVAC repair cost guide; homeowner-reported figures from public forum threads, marked as reported (retrieved August 2026). Figures vary by region, severity and after-hours timing.
Figures last checked
The frozen-coil case is the cheapest of the three if you catch it early, because a filter and some patience is often the entire fix. The capacitor is the most common. Refrigerant is the one where the quoted price and the real price diverge most, because a recharge and a leak repair are different purchases.
Full rate structure, including the after-hours multiplier and what a fair diagnostic fee looks like, sits in our breakdown of what emergency HVAC repair costs.
Emergency Services 24H is a referral service. We do not employ HVAC technicians and we do not carry out repairs or refrigerant work.
Your request routes by ZIP code to licensed, insured contractors covering your area, and they contact you directly to quote and schedule.
Straight answers
The questions homeowners actually search for on this problem, answered in plain language.
Browse all guidesStart by looking at the outdoor unit. If it is not running while the indoor fan is, the usual cause is a failed run capacitor. If it is running normally, the cause is more likely refrigerant or a frozen indoor coil. Check the filter and look for ice on the copper lines before you call anyone.
Yes, with one exception. If there is ice on the refrigerant lines or the indoor coil, switch the thermostat to fan only and leave it running so the ice can thaw. Otherwise turn it off, because running a system that cannot remove heat risks the compressor for no benefit.
It means the system is still moving air but no longer removing heat from it. Three causes account for most cases: a frozen evaporator coil caused by restricted airflow, a failed run capacitor that has stopped the outdoor compressor, or a refrigerant charge that has leaked away.
The signs are ice on the larger copper line at the outdoor unit, very long run times with poor cooling, and sometimes an oily residue at line joints where refrigerant oil has escaped with the gas. Confirming it needs gauges, and handling refrigerant in the US requires EPA certification.
Only as a stopgap, and only if you know that is what you are buying. Refrigerant is not consumed in normal operation, so a low charge means it leaked out and will leak out again. Ask for a leak search and a repair quote alongside the recharge price rather than instead of it.
Most systems will not restart the compressor for three to five minutes after it stops, because restarting against system pressure damages it. If your AC has just cut out and is blowing room-temperature air from the fan, wait the delay out before concluding the compressor has failed.
Checked . If a figure here no longer matches its source, that is a bug, so tell us and we will correct it.
24/7 dispatch network
Tell us what has failed and where you are. We route your request to licensed, insured contractors covering your ZIP code, and they contact you directly.
Fire, a gas smell, or an injury? Leave the building and call 911 first, then your gas utility or power company. Use this form once you are safe.