Tech is doing an A/C 'recharge' on a 2010 Impala: he screws a 12-oz can with sealer onto the low side, runs the engine, watches the low-side gauge until it reads 35 psi, and calls it done.

This tech has made several critical errors:

1. Wrong refrigerant amount: A 2010 Impala requires approximately 13-14 oz of R134a total. Adding a full 12-oz can with sealer likely overcharged the system. Proper charging requires weighing the refrigerant added, not just dumping a can.

2. Incorrect gauge reading: 35 psi on the low side doesn't indicate proper charge. Low-side pressure varies with ambient temperature and should be checked against a pressure/temperature chart. At 75°F ambient, a properly charged system should read around 25-30 psi on the low side.

3. Sealer contamination: Adding sealer to a system that may not have had a leak is problematic. Sealers can clog orifice tubes, expansion valves, and cause compressor failure. Sealers should only be used as a last resort on confirmed leaks.

4. No high-side verification: Proper A/C service requires checking both high and low side pressures, plus superheat/subcooling calculations.

5. No leak diagnosis: If the system was low, there's a leak that needs repair before recharging.

Correct procedure: Recover and evacuate the system, repair any leaks, install proper amount of PAG oil, charge by weight per manufacturer specifications, and verify operation with both pressure readings and temperature testing.

This improper service could lead to poor cooling performance, compressor damage, or complete system failure. This should be corrected by recovering the refrigerant, evacuating the system, removing the sealer contamination, and properly recharging.

He has likely overcharged the system, contaminated it with sealant, and failed to verify actual performance. Here is the breakdown:

1. Charging by Pressure Alone is Wrong (SAE J2788) You cannot charge an automotive A/C system by low-side pressure target. The correct charge is a specific weight of refrigerant (e.g., 1.5 lbs / 24 oz), found on the under-hood label. A 12-oz can is rarely the correct total capacity. Low-side pressure varies wildly with ambient temperature, humidity, blower speed, and engine RPM. 35 psi might be correct at 75°F ambient but indicates severe overcharge at 95°F.

2. Sealant ("Stop Leak") Contaminates the System

• Compressor Damage: Sealant reacts with moisture/air to harden. It ruins the compressor, TXV/orifice tube, and condenser micro-channels.
• Recovery Machine Contamination: If a shop later hooks up a recovery machine, the sealant destroys the machine’s compressor and filters. Many shops will refuse service on a "sealed" system.
• OEM Prohibition: GM (and most OEMs) explicitly voids warranty and prohibits sealant use (GM Bulletin #09-01-38-004).

3. No Vacuum Pull / Non-Condensables He added refrigerant on top of air/moisture already in the system. Air raises head pressure (reducing cooling); moisture creates acid and ice blockages. Proper procedure requires a deep vacuum (500 microns) held for decay testing before charging.

4. No Performance Verification "Done" requires measuring vent temperature (should be 38–48°F at max cool/recirc) and verifying high-side pressure against ambient temperature charts. Low-side pressure alone tells you nothing about heat rejection.

Correct Procedure:

1. Recover any remaining charge (EPA 608).
2. Pull vacuum to 500 microns; hold 15+ min.
3. Charge by weight (scale) with virgin R-134a (no sealant).
4. Verify vent temps & high/low pressures per OEM chart.