Q: How long can I postpone replacing leaking A/C compressor

There really is not a time limit. Once most of the refrigerant has leaked out of the system, the compressor will not turn on. There is nothing you can do to turn the compressor on from inside the car. At this point, no real harm is being done. Here are some things that do harm the system:

• (1) The worst thing you can do is to keep adding refrigerant to keep the system working. There is oil inside the system. It leaks out along with the refrigerant.

• (2) Moisture also harms the system. When it mixes with refrigerant, it becomes acidic and corrodes the system from the inside out. It also does not lubricate. When you open the system to replace parts, it’s imperative to put it into a deep vacuum to remove all the air and moisture before charging. This requires a deep vacuum pump.

• (3) Debris. The compressor is basically a small 6 cylinder piston engine. There are not any filters in the AC system. It should be flushed every time a major component is replaced. Debris from an old compressor can ruin a new one very quickly.

• (4) Running the system low on refrigerant. Since you know you have a leak and are going to have it fixed, I would have the system evacuated until it is repaired. This assures the compressor will not turn on. Liquid refrigerant is what circulates the oil in the system. When there is very little of it, then very little oil, if any, will circulate.

The kit your mechanic mentioned, contains all the parts that should be replaced. The compressor, the desiccant bag, the expansion valve, and O-rings. The desiccant bag is a sock full of pellets that absorb moisture. Once they are saturated, it becomes useless and needs replaced. It is located inside the condenser. The condenser usually needs to be removed to replace the desiccant.

The expansion valve is the only other part of the system that has moving parts. It regulates the flow and pressure to maintain the proper temperature of the evaporator. O-rings are the seals where two parts meet. The system will need to be flushed. You can buy AC flush solvent by the quart. I have found it best to pour it into sections of the system, one at a time. Then blow it out with compressed air.

I usually don’t recommend servicing your own AC system, but if you are pretty handy, have the proper hand tools, have a manual, and can rent or borrow the special tools you need, it can be done properly. However, the best way to save money with AC repairs is to repair it correctly the first time.