AC Not Cooling? 5 Parts You Can Replace Yourself (And How Much You’ll Save)
It’s 100 degrees in Dallas and your AC just stopped cooling. Before you call a pro and spend $300–$800, here are five parts you can diagnose and replace yourself — most in under an hour, with basic tools.
We sell all five of these parts at Open To Public HVAC Parts in Dallas, and we’ll test your old part at the counter for free to confirm it’s actually bad before you buy anything.
1. Run Capacitor — The #1 Most Common AC Failure
Symptoms: AC hums but won’t start. Outdoor unit buzzes but the compressor doesn’t kick on. Fan might spin but cooling doesn’t happen.
What it does: The run capacitor stores an electrical charge that helps the compressor and fan motor start and run efficiently. It’s a small metal cylinder inside your outdoor unit, usually silver or gray.
DIY cost: $10–$30 at our store
Pro cost: $150–$350 (including labor)
Difficulty: Easy. Turn off power, discharge the old capacitor, swap it out. 10–15 minutes. Match the MFD value exactly — the voltage can be equal or higher (440V replaces 370V, not the other way around).
Use our Capacitor Cross-Reference Chart to find your replacement, or just bring the old one in.
2. Contactor — The Electrical Switch That Sends Power to the Compressor
Symptoms: AC clicks but doesn’t start. You hear a clicking sound from the outdoor unit but nothing else happens. Or the opposite — the contactor welds shut and the AC runs nonstop.
What it does: The contactor is a relay switch inside the outdoor unit. When the thermostat calls for cooling, the contactor closes and sends power to the compressor and fan motor. When the contacts get pitted or burnt, it can’t make a clean connection.
DIY cost: $18–$35
Pro cost: $150–$300
Difficulty: Easy. Same access point as the capacitor. Turn off power, note which wires go where (take a photo first), swap the contactor. 15–20 minutes. Match the amp rating and coil voltage.
Read our AC Clicking But Not Starting troubleshooting guide for step-by-step diagnosis.
3. Condenser Fan Motor — The Fan on Top of Your Outdoor Unit
Symptoms: The outdoor unit runs but the fan on top isn’t spinning, or it spins slowly and wobbles. You might hear the compressor running (loud humming) but no air blowing out the top.
What it does: The condenser fan motor pulls air across the condenser coils to release heat. Without it, the refrigerant can’t cool down and your AC blows warm air. The system will eventually overheat and shut off.
DIY cost: $120–$180
Pro cost: $400–$1,200
Difficulty: Moderate. You’ll need to disconnect wiring, remove the old motor from the fan shroud, mount the new one, and reconnect. About 30–90 minutes. Bring the old motor in — we need the HP, RPM, voltage, rotation, and shaft size to match it. Or bring your unit’s model number and we’ll cross-reference it.
For motor manufacturers’ specs, check Gemaire’s technical resources or Trane’s homeowner resources for model-specific part lookups.
Read our AC Fan Not Spinning troubleshooting guide for diagnosis help.
→ Browse condenser fan motors in stock
4. Hard Start Kit — Helps an Aging Compressor Start Under Load
Symptoms: AC struggles to start, especially on hot days. The compressor tries to kick on, hesitates, then either starts after a long delay or trips the breaker. This usually means the compressor is weakening but isn’t dead yet.
What it does: A hard start kit gives the compressor a temporary boost of starting torque — think of it like jumper cables for your AC. It doesn’t fix the underlying issue, but it can buy you another season or two before the compressor needs replacement.
DIY cost: $25–$40
Pro cost: $150–$300 (or they skip it and sell you a new compressor)
Difficulty: Easy. It connects to the existing run capacitor and compressor terminals with two wires. 10 minutes. We’ll show you which terminals to use at the counter.
→ Browse hard start kits in stock
5. Thermostat — The Simplest Swap of All
Symptoms: Display is blank, won’t turn on, or shows the wrong temperature. The AC doesn’t respond when you adjust the settings. Batteries are fine but it’s still unresponsive.
What it does: The thermostat is the brain of your HVAC system. When it fails, it can’t tell the AC to turn on. Sometimes the issue is a dead transformer (which we also carry), but often a thermostat replacement is the fix.
DIY cost: $25–$80 depending on features
Pro cost: $150–$400
Difficulty: Very easy. Turn off power, take a photo of the existing wiring, remove old thermostat, mount new base plate, reconnect wires by color. 15–30 minutes. No special tools needed beyond a screwdriver.
We carry Braeburn thermostats — simple, reliable, and a fraction of the cost of Nest or Ecobee. Read our Thermostat Not Working guide if you’re not sure whether the thermostat is actually the problem.
Before You Start: Safety First
Every repair above starts the same way: turn off the power. For outdoor unit work (capacitor, contactor, motor), flip the disconnect switch next to the unit AND turn off the breaker at the panel. For thermostat work, turn off the system at the breaker. Capacitors hold a charge even after power is off — discharge them before touching anything.
Not Sure What’s Wrong? We’ll Help You Figure It Out.
If you’re not sure which part failed, check our HVAC Troubleshooting Guides — we have step-by-step diagnosis for the most common AC and furnace problems. Or just bring the part in and we’ll test it at the counter.
You can also watch our free video tutorials for hands-on walkthroughs of common repairs.
Come See Us
Open To Public HVAC Parts
10226 Plano Rd, Suite 104, Dallas, TX 75238
(214) 340-9421 — call or text
Mon–Fri 10am–7pm | Sat 10am–3pm
500+ five-star Google reviews. 27,000+ parts in stock. Serving DFW homeowners since 1998. No contractor license needed — just walk in.