Why is my AC not working
The most common reasons an AC stops cooling, and how a technician isolates each.
TroubleshootingAC Blowing Hot Air: What to Check First
An AC blowing warm or hot air in an NYC apartment usually means the outdoor unit is off, refrigerant is low, or the thermostat is calling for heat instead of cool. This guide covers each fault, the checks you can safely do, and when to call a technician on (212) 201-9201.
Credentials
- Licensed HVAC contractor
- Fully insured crews
- EPA Section 608 certified
- NYC DOB registered
Certification and license records are available on request while our public verification page is in progress.
Thermostat
Is it set to cool?
Confirm the thermostat is set to cool, that the setpoint is below room temperature, and that the fan is set to auto. In heat pump systems a stuck O/B changeover signal or a wrongly wired thermostat can leave the reversing valve in heating mode — the system runs, but blows hot air. Set-and-forget smart thermostats sometimes revert to auxiliary heat schedules unexpectedly.
Outdoor unit
Is the outdoor unit running?
Listen at the condenser
If silent, the unit is not making cool air, only moving warm room air.
Check the breakers
Reset the breaker for the outdoor unit. A breaker that trips again is a fault.
Check the disconnect
The service disconnect near the condenser must be fully seated with intact fuses.
Look for a humming compressor
A humming unit that never runs is a classic run capacitor failure.
Refrigerant
Low refrigerant charge
If the outdoor unit runs but the indoor supply air is only slightly cool, refrigerant charge is a likely culprit. A refrigerant leak reduces the temperature drop across the coil and the compressor cannot recover. Only an EPA 608 certified technician can measure superheat and subcooling and confirm the leak. Adding refrigerant without finding the leak is a temporary fix and a code violation.
Airflow
Airflow choked at the coil
A very dirty filter or an iced coil chokes airflow. Supply air feels warm because the evaporator temperature is not being transferred to the moving air. Change the filter and wait 24 hours for ice to melt. If cooling returns and then fails again days later, the underlying cause is usually low refrigerant.
Heat pump
Heat pump reversing valve
- Reversing valve stuck in heating position — unit heats when set to cool.
- Solenoid coil on the valve open circuit; the valve never energises for cooling.
- Thermostat wired without correct O/B changeover polarity for the equipment brand.
- Defrost control board failure locking the system in defrost mode.
Frequently asked questions
Why is cool air coming out only slightly cool?
The three usual causes are a fouled coil raising head pressure, a bad run capacitor slowing the compressor, and low refrigerant charge. A technician measures pressures and amp draw to separate them; the diagnostic visit covers that.
Can hot weather cause the AC to blow hot air?
Directly, no. Systems are designed to keep pulling heat out of the room at NYC design temperatures. Indirectly, hot weather exposes a marginal system: a dirty coil or low charge that ran acceptably in June fails in a July heat wave.
My unit is a heat pump. Why does it blow hot air on cool?
The reversing valve is likely stuck in the heating position, or the thermostat is not sending the correct O/B changeover signal for that brand. Both are diagnosable in one visit.
Should I turn the AC off if it is blowing warm air?
Yes, if you cannot resolve it with a thermostat check, filter change and breaker reset. Running the compressor against a fault wastes electricity and can make the fault worse.
How much does it cost to fix an AC blowing hot air in NYC?
A run capacitor fix runs $220 to $450 in NYC. Refrigerant leak isolation is $400 to $1,200. Heat pump reversing valve work is $900 to $1,800. The diagnostic visit that identifies which is $150 to $300.
Keep reading
Related guides
AC leaking water
Water on the floor around an AC: drain pan, drain line, sleeve tilt and pump failures.
Leak diagnosisAC service cost in NYC
What a diagnostic, a capacitor swap and a refrigerant leak actually cost in New York.
Pricing
Related services
When it is time to call a technician
Central AC repair
Capacitor, contactor, refrigerant charge and thermostat wiring faults.
Same-day AC repair
Hot air is a same-day fault when the outdoor unit is not running.
Get service
Request a quote or call us directly
Call (212) 201-9201 or send the symptom, building type and equipment through the quote form.
- Address
-
517 E 77th St
New York, NY 10075 - Phone
- (212) 201-9201
- info@acrepair.nyc
- Hours
-
Monday–Friday 8:00–18:00
Saturday 9:00–15:00
Sunday closed · emergency line answered 24/7 - Service area
- Manhattan, Brooklyn, Queens