A "dead compressor" and "the whole system is shot" are the two most expensive things a homeowner can be told, and two of the most commonly misdiagnosed. The good news: this is exactly the situation where slowing down and getting a second opinion is cheap insurance on a multi-thousand-dollar decision. Here's how to tell a real diagnosis from a sales pitch.
A compressor is one of the priciest parts in your system (roughly $1,300–$2,800+ installed) and it's often under warranty for years, which can change the math completely. Crucially, a failed capacitor or contactor (cheap parts) can look identical to a dead compressor to a homeowner. So before you approve a compressor replacement or a whole new system, ask the tech to show you the readings: the pressures and the electrical/continuity test on the compressor. If they can't or won't back the claim with diagnostics, that alone is your answer to call someone else. This is the call where a second opinion pays for itself.
The symptom that screams "dead compressor" (the outdoor unit hums but won't start, or trips the breaker) is the same symptom you get from a failed start capacitor or a burnt contactor. Those are $10–$30 parts with cheap labor. A compressor is a four-figure job.
A careful tech rules out the cheap causes first. A rushed (or commission-motivated) one can jump straight to "your compressor's gone, and honestly at this age you should just replace the whole system." Sometimes that's right. But you can't tell the difference from the driveway, so you ask to see the evidence.
| The real problem | Typical installed | Looks like a dead compressor? |
|---|---|---|
| Start/run capacitor | $150–$400 | Yes. Hums, won't start. Cheap to rule out first. |
| Contactor | $150–$350 | Yes. Clicks/buzzes, won't engage. |
| Hard-start kit (assist) | $150–$400 | Can revive a struggling (not dead) compressor. |
| Compressor replacement | $1,300–$2,800+ | The real thing. Needs readings to confirm. |
| Full system replacement | $5,000–$12,000 | A separate decision, never a same-day one. |
You don't need to be an HVAC tech. You just need to ask them to show you what they measured. A good diagnosis leaves evidence:
A tech who diagnosed it properly will happily walk you through these. Reluctance to show the readings ("trust me, I've seen it a hundred times") is the single biggest reason to get a second opinion.
Even when the compressor really is dead, replacing it isn't automatically the right move, and replacing the whole system isn't automatically wrong. The honest factors:
| Lean toward repairing the compressor | Lean toward replacing the system |
|---|---|
| Unit is under ~8 years old | Unit is 12+ years old |
| Compressor is under warranty (you owe only labor) | Out of warranty + uses phased-out R-22 refrigerant |
| Rest of the system is in good shape | Repeated failures / multiple aging components |
| You're not planning to move soon | The efficiency upgrade genuinely pays back for your climate |
The clean way to decide: get both numbers in writing, the compressor repair and the full replacement, and compare cost-per-remaining-year. And treat them as two separate decisions; a repair visit should never be the moment you sign a five-figure replacement under pressure.
If the compressor call turned into a quote for a whole new system, run that number before you sign. Our free autopsy tool reads it line by line: fair, padded, or missing.
Run the free quote autopsy →The readings to ask to see, the warranty questions, and the repair-vs-replace factors, on one page, so you can take it to the conversation before you approve a four-figure job. One email, no spam.
A compressor replacement typically runs $1,300–$2,800 or more installed, depending on size and system type. But if the compressor is still under the manufacturer's parts warranty (often 5–10 years), you may owe only labor and refrigerant, which can drop the cost to a few hundred dollars. Always check the warranty before approving the job.
Yes, this is one of the best times to get one. A compressor replacement (or a "you need a whole new system" pitch) is a multi-thousand-dollar decision, and the same symptoms can come from a cheap capacitor or contactor. Before approving, ask the tech to show you the pressure readings and the electrical/continuity test on the compressor. If they can't or won't back the claim with diagnostics, get a second opinion.
Yes. A failed start/run capacitor or a burnt contactor produces the same classic symptom (the outdoor unit hums but won't start, or trips the breaker) yet those are $150–$400 repairs versus a four-figure compressor job. A careful technician rules out the cheap causes first. Ask whether the capacitor and contactor were checked before the compressor was condemned.
It depends on age, warranty, and the condition of the rest of the system. Lean toward repair if the unit is under about 8 years old, the compressor is under warranty, and the rest of the system is sound. Lean toward replacement if it's 12+ years old, out of warranty, uses phased-out R-22 refrigerant, or has had repeated failures. Get both numbers in writing and compare cost-per-remaining-year, and never sign a replacement under same-day pressure.
Often, yes. Manufacturers commonly cover compressors for 5–10 years, sometimes longer if the unit was registered. Find your unit's model and serial number and look up the warranty, or ask the contractor to verify it. A covered compressor changes the repair-vs-replace math significantly, so confirm it before you approve any work.