A refrigerant leak gradually empties the AC system until cooling fades. The signs are predictable: oily residue at fittings, declining cooling over weeks, and a system that needs frequent recharges.
O-rings dry out and shrink over the years. Refrigerant seeps slowly, sometimes paired with visible green or oily residue at the fitting. Cheapest leak to fix.
The condenser is in front of the radiator and exposed to rocks. A pinhole leak from impact is common. Look for green dye or oily streaks on the condenser fins.
Evaporator is inside the HVAC box. A leak there is harder to detect and more expensive to fix. Symptom is cooling that slowly fades over a season.
The shaft seal at the front of the compressor wears out. Often visible as oily refrigerant residue around the clutch.
A high-pressure hose develops a crack from heat and vibration. Sometimes audible as a hiss when AC is running.
The cheap Schrader valves at the service ports can develop a slow leak. $5 part, easy fix once located.
These canisters can corrode at the seams. Less common but possible especially in rust-belt cars.
| Likely Cause | Typical Cost | DIY Difficulty | Severity | Likelihood |
|---|---|---|---|---|
| Leaking O-Rings at Hose Connections | $50-$150 O-rings + 1-2 hrs | Moderate | Low | 60% |
| Condenser Damaged by Road Debris | $300-$800 condenser + 2-4 hrs | Hard | Medium | 45% |
| Evaporator Leak | $800-$1,500 + 4-8 hrs | Hard | High | 35% |
| Compressor Front Seal Leak | $400-$1,200 compressor | Hard | Medium | 25% |
| Cracked Hose or Fitting | $80-$300 hose | Moderate | Medium | 20% |
| Service Port Schrader Valve | $5-$20 valve | Easy | Low | 15% |
| Receiver-Drier or Accumulator | $50-$200 part + 1-2 hrs | Moderate | Low | 10% |
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If your scanner is showing one of these, that is your starting point. Tap any code for full causes and repair costs.
Cooling fades over weeks or months. You may see oily residue at fittings. The system requires recharging more often than annually. A UV dye test confirms.
Modern systems lose less than 0.1 lb of refrigerant per year. If you need a recharge every summer, you have a real leak that needs repair.
With UV dye and a black light, yes. Have the system charged with dye, run it for a week, then inspect with the light. Glowing yellow-green is refrigerant oil with dye.
O-ring: $80-$150. Hose: $150-$300. Condenser: $400-$800. Evaporator: $800-$1,500. Compressor: $800-$1,500.
As a last resort only. It can plug small leaks but can also clog the expansion valve and damage the compressor. Most shops will refuse to service a system with it.
R134a and R1234yf are not toxic in normal concentrations, but venting refrigerant into the atmosphere is illegal in most places. Fix the leak rather than topping off.
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