How to Swap Out a Failed Compressor Like a Pro
By Stan Johnson | Master HVAC Technician & Educator
A dead compressor is like a heart attack for your AC—without it, your system can’t pump refrigerant, and cooling stops completely. While compressor replacement is a big job, it’s doable with the right tools and safety precautions.
In this guide, I’ll walk you through exactly how I replace compressors in the field—step by step. Whether you’re a DIY warrior or just curious about the process, you’ll learn:
✔ How to diagnose a bad compressor
✔ Safety must-dos (high-voltage & refrigerant risks)
✔ The full replacement process
✔ When to call a pro instead
Let’s dive in.
⚠️ Safety Alert: Is This a DIY Job?
Compressor replacement involves:
✔ High-voltage electrical work (240V can be lethal)
✔ Handling EPA-regulated refrigerants (Illegal to vent!)
✔ Specialized tools (Recovery machine, torch, vacuum pump)
Only attempt this if you’re EPA 608 certified and experienced with HVAC electrical systems. Otherwise, call a licensed pro—this isn’t a beginner repair!
Step 1: Confirm the Compressor is Really Dead
Symptoms of Failure:
Loud humming but no cooling
Tripped breaker when AC starts
Burned/melted wires at the compressor
0 ohms between terminals (short circuit) or infinite resistance (open circuit)
Diagnostic Tests:
Check voltage at contactor (should be 240V).
Test capacitor (weak cap can mimic compressor failure).
Ohm out compressor terminals (C to S, C to R, S to R).
Pro Tip: If the compressor is locked up, a hard start kit might revive it temporarily—but replacement is inevitable.
Step 2: Recover Refrigerant (EPA-Required Step)
You MUST recover refrigerant legally!
Connect recovery machine to service ports.
Pump refrigerant into an approved recovery tank.
Weigh tank to ensure full evacuation.
Warning: Venting refrigerant = $10,000+ EPA fine. Never skip this step!
Step 3: Disconnect Electrical & Remove Compressor
Kill power at the breaker + verify with a voltage tester.
Label and disconnect wires (Common, Start, Run).
Cut refrigerant lines with a tubing cutter.
Unbolt compressor (usually 3-4 bolts on rubber mounts).
Pro Tip: Take photos before disassembly—you’ll need them for reassembly!
Step 4: Install New Compressor
Position new compressor on rubber isolation mounts.
Braid new connections (Use nitrogen while brazing to prevent carbon buildup).
Replace filter drier (MUST be changed with compressor).
Reconnect electrical (Match C, S, R terminals exactly).
Critical Note: Never leave the system open—moisture contamination kills compressors fast!
Step 5: Pressure Test & Evacuate
Pressurize with nitrogen (150-200 PSI) and check for leaks (soap bubbles).
Evacuate with vacuum pump (500 microns or lower).
Hold vacuum for 30+ minutes to ensure no leaks.
Pro Mistake I’ve Seen: Skipping the vacuum step = acid formation and early death of the new compressor.
Step 6: Recharge Refrigerant & Test
Weigh in exact refrigerant charge (per manufacturer specs).
Start system, check amp draw (compare to RLA on compressor label).
Verify superheat/subcooling with manifold gauges.
Golden Rule: Overcharging is just as bad as undercharging—measure carefully!
Step 7: Monitor Performance
Listen for abnormal noises
Check temperature drop (15-20°F at vents)
Verify stable amp draw
Red Flag: If the new compressor draws high amps, shut it down—you may have a restriction or wiring issue.
When to Call a Professional
✔ No EPA 608 certification (Refrigerant handling is illegal without it)
✔ Unsure about electrical wiring
✔ System uses R-22 (Old refrigerant = $$$ recharge costs)
Cost Note: Compressor replacement often runs 3,500. If your AC is over 10 years old, replacing the entire unit may be smarter.
Pro Tips to Extend Compressor Life
✔ Change filter drier with every major repair
✔ Install a hard start kit (Reduces strain on startup)
✔ Keep coils clean (Dirty coils = overheated compressor)
Final Thought: Prevention Beats Replacement
Most compressors die from dirty coils, low refrigerant, or voltage issues—not old age. Annual maintenance could save you from this costly repair!
Read More: Types of AC repairs
Ever replaced a compressor? Share your battle stories below!
Stay cool (and safe),
Stan Johnson
HVAC Pro Tips YouTube | EPA 608 Certified
