DIY troubleshooter · causes ranked by how often each turns out to be the problem, in our judgment (no dataset ranks them)
Nothing happens when the thermostat calls for cooling: no fan, no click, or an outdoor unit that stays silent. Trace the power from the thermostat to the breaker to the outdoor disconnect.
Source: HVACPro analysis of 1,611 homeowner-reported quotes and invoices in public Reddit posts dated 2025-01-01 to 2026-09-29. Each price is the median of the reports for that job, and "most" is the middle half of them (25th to 75th percentile). Homeowners reported these prices and we did not verify them.
Simplified drawing, not to scale. Real systems vary: the indoor unit can sit in an attic or closet, the ducts can run in the attic or under the floor. Original illustration, not a photo.
Stock photo, not our work. Photo by Anh-Bao Tran-Le via Pexels.
How to checkConfirm Cool mode, a set point below room temperature, and fresh batteries. A compressor short-cycle delay of 3 to 5 minutes after any stop is normal.
Typical repair costFree to check.
How to checkOpen the panel and look for a breaker in the middle position. The AC uses a two-pole breaker for the outdoor unit and a separate one for the air handler.
Typical repair costFree to check.
How to checkA metal box on the wall near the outdoor unit holds a pull-out block or switch. Someone may have pulled it during yard work.
Typical repair costFree to check.
How to checkAn air handler that is dead only after rain or on hot humid days may be shut off by the pan float switch.
Typical repair costFree to check.
How to checkThe indoor fan runs and the thermostat is calling, but the outdoor unit does not start. A stuck or pitted contactor or a dead capacitor is a common reason.
Typical repair costContactor: Too few reports to price (3); Capacitor: Median $310 (most $220–$400), 26 homeowner reports
How to checkOutdoor unit hums or clicks and trips the breaker soon after starting.
Typical repair costCapacitor: Median $310 (most $220–$400), 26 homeowner reports; Compressor: Median $3,000 (most $1,900–$4,000), 43 homeowner reports
Ranks are editorial, not measured. A price is what homeowners reported for that one part or job, not a quote for the cause on that row, and a cause can involve more than one part. Source: HVACPro analysis of 1,611 homeowner-reported quotes and invoices in public Reddit posts dated 2025-01-01 to 2026-09-29. Each price is the median of the reports for that job, and "most" is the middle half of them (25th to 75th percentile). Homeowners reported these prices and we did not verify them.
$190
Median pro diagnostic visit, from 62 homeowner reports
Source: HVACPro analysis of 1,611 homeowner-reported quotes and invoices in public Reddit posts dated 2025-01-01 to 2026-09-29. Each price is the median of the reports for that job, and "most" is the middle half of them (25th to 75th percentile). Homeowners reported these prices and we did not verify them.
These checks need no tools beyond a screwdriver, a hose, or a vacuum. Do them in this order.
1 Thermostat
7 Breaker panel and outdoor disconnect
7 Breaker panel and outdoor disconnect
5 Condensate drain line, pan and float switch
The causes below are not DIY, and we give no repair steps for them. Each carries a specific danger.
Stock photo, not our work. Photo by Bingqian Li via Pexels.
Open
Need a licensed HVAC pro in the Tampa Bay outer ring? Call and we'll connect you with a licensed local contractor.
HVACPro is a free referral service for homeowners, not an HVAC company. We don't do the work, and we may be paid by the contractor. Check any contractor's license on the state's lookup before you hire.
Every city below has an A-to-Z list of the businesses with an active Florida HVAC license there. The number on each chip is that count.
Counts: businesses with an active license and a city address in the Tampa Bay outer ring, from FL DBPR construction licensee extract (CONSTRUCTIONLICENSE_1.csv), retrieved 2026-10-05. A license says the state permits the work, not that the work is good.
A pro visit starts with a diagnostic fee. Homeowners reported: Median $190 (most $100–$290), 62 homeowner reports. The repairs behind the causes on this page:
Reported price, U.S. dollars
Source: HVACPro analysis of 1,611 homeowner-reported quotes and invoices in public Reddit posts dated 2025-01-01 to 2026-09-29. Each price is the median of the reports for that job, and "most" is the middle half of them (25th to 75th percentile). Homeowners reported these prices and we did not verify them.
| Repair | Median | Most (middle half) | Reports |
|---|---|---|---|
| Contactor | Too few reports to price | 3 | |
| Capacitor | $310 | $220–$400 | 26 |
| Compressor | $3,000 | $1,900–$4,000 | 43 |
These are national prices. We do not have enough Tampa Bay outer ring reports to publish a local one.
If the repair ends in a full replacement, the closest local cut is Florida: a median of $12,000 (most $9,400–$15,600) across 55 full-system reports, against $13,650 across 588 reports nationwide. See the AC repair cost guide and the AC replacement cost guide for every repair and job we have enough reports to price.
Source: HVACPro analysis of 1,611 homeowner-reported quotes and invoices in public Reddit posts dated 2025-01-01 to 2026-09-29. Each price is the median of the reports for that job, and "most" is the middle half of them (25th to 75th percentile). Homeowners reported these prices and we did not verify them.
A pro fix for this symptom can end in a replacement. If it does, these Tampa Bay outer ring utility programs pay for qualifying equipment. Confirm your utility and eligibility first.
| Program | Utility | Amount |
|---|---|---|
| Home Energy Improvement: AC replacement | Duke Energy Florida | $300 |
| Home Energy Improvement: heat pump upgrade | Duke Energy Florida | $500 |
| Home Energy Improvement: strip-heat replacement (high efficiency) | Duke Energy Florida | $600 |
| Home Energy Improvement: strip-heat replacement (higher efficiency) | Duke Energy Florida | $1,000 |
| Energy Efficient Heat Pump Rebate | Lakeland Electric | $450 (mini split $225 per condensing unit) |
| HVAC Annual Maintenance Rebate | Lakeland Electric | Up to $100 per year (the cost of the inspection) |
| Heating & Cooling Program: standard tier | Tampa Electric | $40 for SEER 16.0 / SEER2 15.2 |
| Heating & Cooling Program: high-efficiency tier | Tampa Electric | $550 for SEER 17.0 / SEER2 16.2 |
Stock photo, not our work. Photo by HUUM │sauna heaters via Pexels.
Work through the checks in the order Trane lists them. First, the thermostat: replace the batteries if the screen is blank, set it to Cool with the fan on Auto, and set the temperature below the indoor temperature. Second, power: confirm the indoor shutoff switch is on and check the breakers for the indoor and outdoor units.
Trane says not to flip a tripped breaker and to call a professional, because it may have tripped from a serious problem. Third, replace a dirty air filter. Fourth, a clogged drain line can shut the system down if it has a condensate safety switch.
Fifth, a frozen evaporator coil can shut the unit off. Sixth, a bad start or dual capacitor keeps the unit from turning on and needs a technician.
Checked against: Trane: AC Not Turning On. Pages opened 2026-09-30.
Carrier and Trane differ on the first reset. Carrier says to turn the breaker fully off, wait about 5 minutes, then switch it back on. Trane says not to flip a tripped breaker and to call an HVAC professional.
Either way, if it trips again, leave the system off and have a qualified HVAC professional inspect it for an electrical fault. The U.S. Consumer Product Safety Commission lists an appliance that repeatedly trips a circuit breaker as a defect that could cause a fire or shock hazard.
Checked against: Carrier: AC Unit Not Turning On? Troubleshooting Steps & Solutions; Trane: AC Not Turning On; U.S. CPSC: CPSC Guide to Home Wiring Hazards. Pages opened 2026-09-30.
Checking it is a standard step: Carrier lists a disconnect that was turned off or pulled out as a common reason an air conditioner will not turn on. Do not open the box or the unit's panel.
OSHA notes that there is still power to the supply side of a disconnect, and Lennox warns that line voltage is present at all components of units with single-pole contactors when the unit is not running. Lennox says to disconnect all remote electric power supplies before opening an access panel.
Checked against: Carrier: AC Unit Not Turning On? Troubleshooting Steps & Solutions; Lennox: XP17 Air Conditioner Installation Instructions (506586-01); OSHA: Letter of interpretation on 29 CFR 1910.333 and 1910.147 (July 28, 2006). Pages opened 2026-09-30.