Carrier Air Conditioner Not Cooling - Quick Fix Guide [2026]

Quick Fix Summary

Most Carrier air conditioners stop cooling due to a simple airflow or power issue. The fastest fix is to confirm the thermostat is set to Cool with a setpoint at least 3-5 F below room temperature, replace a dirty filter, and reset power to both the indoor unit and the outdoor condenser for 5 minutes to clear safety lockouts. In many cases, cleaning the outdoor coil and restoring airflow solves the problem quickly.

What Causes This Problem

Several common root causes lead to a Carrier air conditioner that runs but does not cool. Understanding why they happen will help you target the right fix.

• Restricted airflow (dirty filter, iced coil, blocked vents): When airflow drops, the evaporator coil can get too cold and freeze. A frozen coil cannot absorb heat, so supply air feels warm. Dirty filters, closed registers, and clogged evaporator fins are usual culprits.
• Outdoor coil issues (dirty condenser, failed fan, bad capacitor): Your condenser must dump heat outdoors. If the coil is covered in debris or the fan is not moving enough air due to a failed motor or run capacitor, head pressures climb, system safety trips, and cooling performance plummets.
• Control or power problems (tripped breaker, float switch, low-voltage signal): Carrier systems use safety circuits such as condensate overflow float switches and pressure switches. A tripped float switch or a breaker issue can interrupt the 24VAC cooling call (Y), stopping the compressor while the blower may still run.
• Refrigerant issues (leak, low charge, metering device fault): Low refrigerant from a leak, or a stuck/failed TXV (thermostatic expansion valve), reduces heat transfer. The result can be longer run times, poor cooling, or coil freeze. Refrigerant work requires EPA-certified handling and specialized tools.
• Thermostat or control board faults: Misconfigured schedules, dehumidify settings, or an internal fault in the thermostat or control board can prevent proper compressor staging. Carrier Infinity systems may display alerts or fault codes that indicate communication or equipment problems.

Step-by-Step Troubleshooting

1. Verify thermostat settings and delays.

   Set the thermostat to Cool, Fan to Auto, and lower the setpoint at least 3-5 F below the current room temperature. Many Carrier controls enforce a 3-5 minute compressor anti-short-cycle delay; after changing modes, wait a few minutes for the outdoor unit to start. If you use a Carrier Infinity Touch Control, check for active alerts by pressing Menu > Service > Alerts (wording can vary slightly by model).

2. Check power to indoor and outdoor units.

   Locate and reset both breakers: one for the air handler or furnace (indoor unit) and one for the outdoor condenser. Flip each breaker fully Off and back On. Also check the outdoor disconnect (usually a pull-out or breaker near the condenser). If either unit lacks power, cooling will fail even if the blower runs.

3. Perform a system reset to clear lockouts.

   Turn the thermostat to Off. Kill power to the indoor and outdoor units at their breakers for 5 minutes to clear pressure switch or board lockouts. Restore power, set the thermostat to Cool, Fan Auto, and reselect a lower setpoint. On Infinity Touch, you can also reboot the thermostat by gently pulling it off the wall base for 30 seconds and reseating it, or use Menu > Settings > Reset (if available).

4. Replace or clean the air filter.

   A clogged filter is the top cause of poor cooling and frozen coils. Replace the filter if it looks dirty or is past its recommended interval. Typical sizes include 16x25x1, 20x25x1, or 16x20x1; choose a MERV rating that matches your system and ductwork (often MERV 8-11 for residential). After replacing, run the system and check if airflow improves.

5. Open supply registers and return grilles.

   Ensure all vents are open and unobstructed. Closed dampers or blocked returns reduce airflow and can cause coil icing. Vacuum dust from grilles, and confirm furniture or rugs are not covering registers. If you have zoning dampers, make sure the cooling zone is open.

6. Check for a tripped condensate float switch.

   Many Carrier air handlers include a float switch (SS1) in the drain pan. If the drain is clogged, the float opens the safety circuit and can stop the outdoor unit from running. Inspect the drain pan for standing water. Clear the drain line with a wet/dry vac at the outside termination, then flush with distilled vinegar. After clearing, reset power and try cooling again.

7. Inspect the outdoor unit operation.

   Go outside and observe the condenser. The fan should run and you should hear the compressor after the delay period. Carefully feel the larger insulated refrigerant line (suction line); it should become cool to cold after a few minutes. If the fan is not spinning while the compressor hums, suspect a bad fan motor or run capacitor. If neither starts, check low-voltage signal (24VAC) at the contactor (for pros only).

8. Clean the condenser coil.

   Turn off the outdoor disconnect or breaker. Remove debris/leaves from the coil fins and straighten bent fins with a fin comb. Rinse the coil from inside out with a gentle hose spray (do not pressure wash). Use a non-acid coil cleaner if needed. Let it drain, restore power, and test cooling. Dirty coils frequently cause high-pressure trips and poor cooling.

9. Check for evaporator coil icing.

   If airflow is weak or supply air feels warm, open the blower compartment or look at the coil area for frost or ice. If iced, turn the thermostat to Off and set the fan to On for 60-90 minutes to thaw. Root causes include dirty filters, closed vents, low blower speed, or low refrigerant. After thawing, resume cooling and monitor; if ice returns quickly, proceed to professional diagnostics.

10. Review Infinity or comfort control alerts/faults.

    On Carrier Infinity Touch, go to Menu > Service > Alerts or Menu > Service > Check System to read active faults. Common messages may indicate outdoor unit communication issues, pressure switch trips, or high/low temperature alerts. If your outdoor unit has a Comfort Alert diagnostic module (a small board with LEDs), note the LED blink code and read the fault legend printed on the module label; it will identify faults such as high pressure, low pressure, locked rotor, or open circuit. Use those clues to direct cleaning, airflow, or professional service.

11. Evaluate and test capacitors and the contactor (advanced DIY).

    With power off, visually inspect the dual run capacitor in the condenser for bulging or leaking. Many systems use a dual run capacitor (e.g., 35/5 uF, 440V). If you own a meter that reads microfarads, test and compare to the label values. Inspect the contactor for pitted or welded contacts; the coil should energize at 24VAC. Typical service replacements include a dual run capacitor (example aftermarket: P291-3554) and a 2-pole 30A contactor. If unsure or uncomfortable, call a pro; these parts are high voltage.

12. Check low-voltage cooling call continuity.

    When the thermostat calls for cooling, the Y signal should deliver 24VAC to the condenser contactor. If the outdoor unit does not energize, trace Y through any float switch, the thermostat, and the air handler board. A broken wire, tripped float, or blown low-voltage fuse (often a 3A-5A automotive-style fuse on the control board) can interrupt the call. Replace the fuse only after finding the short cause.

13. Measure temperature split (delta-T).

    Use a digital thermometer to measure air temperature at the return grille and at a nearby supply register with the system running for 10-15 minutes. A normal cooling delta-T is roughly 16-22 F under typical indoor humidity. A low delta-T suggests refrigerant charge, airflow, or compressor issues; a very high delta-T may indicate restricted airflow.

14. Check blower performance and settings.

    Ensure the blower door is properly closed; the door safety switch will stop the blower if the panel is ajar. On variable-speed ECM blowers (common in Carrier furnaces and air handlers), a fault may show on the thermostat or board. Verify the fan speed setting for cooling matches design airflow; misconfigured dip switches or setup options can starve the coil.

15. Assess refrigerant or TXV problems (call a pro).

    If cleaning, filters, and electrical checks do not restore cooling, a refrigerant leak or metering device issue may be present. Signs include hissing, oily residue on lines, repeated low-pressure fault indications, or rapid re-icing after thaw. These require EPA-certified service to locate leaks, repair, evacuate, and weigh in charge.

Frequently Asked Questions

Why is my Carrier air conditioner running but not cooling?

Most often, airflow is restricted or the outdoor condenser is dirty. A clogged filter, closed vents, or an iced evaporator coil will make supply air feel warm even while the blower runs. Outdoors, a dirty coil or failed fan/capacitor prevents heat rejection, causing high-pressure trips and poor cooling. Start by replacing the filter, opening vents, cleaning the condenser coil, and performing a 5-minute power reset.

How do I reset my Carrier air conditioner?

Turn the thermostat to Off. Shut off the indoor unit and outdoor condenser breakers for 5 minutes. Restore power, set the thermostat to Cool and Fan Auto, and lower the setpoint. On Carrier Infinity Touch Control thermostats, you can view alerts via Menu > Service > Alerts, and reboot the thermostat by removing it from the wall base for about 30 seconds or using Menu > Settings > Reset (if available). This clears common lockouts from pressure switches and control boards.

What error codes do Carrier systems show for cooling issues?

Infinity systems report alerts on the thermostat, such as pressure or communication faults, accessed via Menu > Service > Alerts. Many outdoor units include a Comfort Alert diagnostic module with an LED that blinks codes. The module’s label provides a code legend indicating faults like high pressure, low pressure, locked rotor, or open circuit. Because code mappings vary by model, always read the code legend printed on your unit or thermostat’s service screen.

Carrier AC not cooling but the fan runs. Is the capacitor bad?

If the outdoor fan is not spinning while the compressor tries to run, a failed fan motor or run capacitor is likely. Many condensers use a dual run capacitor (for example, 35/5 uF, 440V). A bulging top or oil leakage is a visual sign of failure. Testing requires a meter that reads microfarads. Replace only with the exact uF/V rating, and cut power first. If you are unsure, call a pro, as improper replacement can damage the compressor.

What temperature drop should I see from my vents?

With normal indoor humidity and steady operation, you should see about a 16-22 F difference between return air and supply air temperatures. For example, if the return is 78 F, the supply near the air handler might be 58-62 F. A significantly lower split points to refrigerant or compressor issues or high indoor humidity; a significantly higher split often indicates restricted airflow.

When to Call a Professional

Call a certified HVAC technician if you see repeated high- or low-pressure faults, rapid re-icing of the evaporator coil even after filter replacement and airflow fixes, or if the outdoor unit will not start despite proper low-voltage signals. Sealed-system work (leak detection, evacuation, charging) is not DIY and requires EPA certification. Electrical component testing beyond visual checks (such as measuring microfarads, locked-rotor current, or diagnosing ECM blowers) is best handled by a pro.

Typical repair cost ranges (vary by region and model):

• Service call and basic diagnosis: $100-$200
• Run capacitor replacement: $120-$300
• Contactor replacement: $150-$300
• Condenser fan motor replacement: $400-$800
• Thermostat replacement (standard): $150-$400; Infinity control: $400-$900
• Clear condensate drain and float switch reset: $120-$250
• TXV replacement: $700-$1,500
• Refrigerant leak repair and recharge: $400-$1,200+
• Compressor replacement: $1,500-$3,000+

Safety note: Always turn off power at the breaker and outdoor disconnect before opening panels. Use proper PPE. Do not attempt refrigerant handling or advanced electrical diagnostics without training.

Replacement Parts

Here are common replacement parts that solve many Carrier air conditioner cooling issues. Use the exact specifications from your unit’s label when ordering. Links are Amazon search queries with your affiliate tag.

• Air filters (common sizes: 16x25x1, 20x25x1, 16x20x1): Replace every 1-3 months in peak season. Search 16x25x1 filter | Search 20x25x1 filter
• Dual run capacitor (example value 35/5 uF, 440V): Verify your exact uF and voltage on the capacitor label. Aftermarket example series: P291-3554. Search dual run capacitor 35/5 440V
• Condenser fan motor capacitor (single value, e.g., 5 uF, 440V): Some systems use separate fan capacitors. Check the motor label for the correct microfarads. Search fan motor capacitor 5 uF 440V
• Contactor (2-pole, 30A, 24VAC coil): Common in residential condensers; match amperage and coil voltage. Search 2-pole 30A contactor 24V
• Hard-start kit (universal): Helps a compressor start under strain; example: Supco SPP6. Use only if recommended for your unit. Search Supco SPP6
• Condenser fan motor (match model, RPM, HP, and rotation): Specs vary by unit; verify with the motor label or Carrier model literature. Search Carrier condenser fan motor
• Coil cleaner (non-acid): For safe condenser coil cleaning. Search condenser coil cleaner
• Thermostat (Carrier-compatible): If your control is faulty, consider a replacement compatible with your system (standard or communicating Infinity as applicable). Search Carrier thermostat

Tip: Always match electrical ratings (uF, voltage, amperage), motor specifications, and wiring to your exact equipment model. When in doubt, consult the unit’s data plate or Carrier technical literature.