DenLorsTools.com Summary: Questions answered by a master tech, regarding a car’s AC system when the Freon just won’t leave the can. When the vehicle’s air conditioning system doesn’t accept a charge of refrigerant there can be many issues, or the problem could be solved easily. Understanding how the system works in easy to understand terms is the best place to start. This and other helpful A/C articles when it’s hot outside and it’s time to get the car’s air con working again.

Question – I have a 2005 Audi A6 3.2Q, that’s been having a/c issues off and on. A/C would blow cold then suddenly hot, and now just hot. I replaced a bad pressure/temp sensor and the o ring, and lost all the r134 in the process. We hooked up a vacuum on the low pressure port for just over and hour and it held -30inHg. We then tried to refill the system with a few cans from AutoZone but it wouldn’t take. Car was running with the a/c on max blower and max cold. Compressor never kicks on, but I’ve read that it won’t with low refrigerant. System only took in about 100g, and no more. A buddy of mine mentioned that we have to vacuum both the high and low pressure ports. Is this what we’re missing? Anthony.

Answer – First, for the benefit of others reading this (and our Ozone) PLEASE have refrigerant recovered properly so it can be recycled instead of being released into our atmosphere when opening up a system for service. The system may not need to be opened to make some repairs. Sometimes the problem could just be electrical, so a second opinion may be worth a trip to the shop anyway.

Anthony, 100g is only 3.5 ounces. But lets back up. You asked about applying vacuum to both low and high sides. The AC manifold gauge set would be hooked to both service ports before hooking up the yellow hose and applying vacuum. See our Car A/C Vacuum Pump Faq’s repair article for more details on how to properly pull a vacuum down before charging.

However, using the vacuum pump improperly, would not be the cause of the Freon not going in. Ever wonder how shops can put refrigerant in without the car running? AC machines use an internal pump to put Freon in a car’s system. A long time ago at a Goodyear store in the 1980’s, I used an old charging station that used a heat blanket that went around the 30 pound container to heat the refrigerant to assist in charging a car’s AC system. These two methods don’t require the car’s engine (or compressor) to be running. But, when you are charging a system with small cans and no special charging station, the vehicle’s compressor is required to come on. After you add some refrigerant, like you did, the pressure will be enough for the compressor to start to come on. The suction (low) side will start to draw the refrigerant in. The compressor will normally cycle on/off rapidly at first until the charge is increased, staying on longer as you come closer to a complete charge. It’s normal for cycling to occur after the complete charge also, to maintain a proper target reading of approximately 30-35 psi on the low side, which prevents evaporator freeze-up.

Seems to me the main problem with your car was electrical to begin with. The compressor wasn’t coming on before and is not coming on now, to be able to complete the charge. I would check to the low pressure switch and the compressor clutch coil. There could be many other possible failures but these are the things I would start with.

The original problem you had still exists. The compressor is not coming on. Except for now you haven’t got much refrigerant in the system. After the electrical issue is resolved the system will capable of accepting a charge (with the compressor operating normally). Good Luck.

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