Recently I received a phone call from an acquaintance who experienced sticker shock from an unexpected air conditioning repair. Naturally they reached out to their “Car Guy” for a deeper understanding of the situation. Here’s what happened: while traveling on the highway a random knocking noise started under the hood. The noise came and went, but was getting louder and more consistent. The driver stopped, popped the hood, and pinpointed the location of the noise: the A/C compressor.
In the past a simple “get by” solution would have been to simply cut the belt that runs the compressor, thus removing the power it gets from the engine. But on a modern car there is usually only one belt, the serpentine belt, which runs EVERYTHING on the engine. The driver was close to his destination and knew a reputable shop, so he pressed on at a slower pace and headed straight to the garage.
The shop came back with an estimate of $1,100 to fix the problem. Wow that is a lot of money! But when you look at the situation it is actually very reasonable. The work order called for the following:
- Remove/replace air conditioning compressor
- Remove/replace air conditioning dryer
- Flush air conditioning system
- Vacuum down air conditioning system, check for leaks
- Recharge air conditioning system with R134a refrigerant
You may ask “but only the air conditioning compressor was bad, is the other stuff necessary?” Yes, yes it is and here’s why. The air conditioning compressor is obviously bad (in this case it had grenaded internally, leading to the nasty noises mentioned). Which leads us to the second item: the air conditioning dryer. When the compressor took itself out, it sent tons of shrapnel through the A/C system. Small metal shards went everywhere and that is bad. The air conditioning dryer is designed to filter and remove contaminants & moisture from the A/C system. The dryer just got blasted with the guts of the air conditioning compressor, and while it does a good job of filtering junk, there is only so much it can take. Also, almost every air conditioning compressor manufacturer REQUIRES that the air conditioning dryer be replaced at the same time as the compressor or else the warranty is void. This is not the time to cheap out folks.
Moving on to the air conditioning system flush. Remember all that metal shrapnel that got blasted through the system? Yeah, that’s bad for new parts. The only way to get all that stuff out is a good, thorough system flush. There are all kinds of places for junk to hide in an air conditioning system. If the repair is going to last then the new parts need to have a clean system to do their work.
Next is the vacuum check of the system (called evacuation). Air conditioning systems are sealed, which is good because they operate under very high pressures. They also use very specific gases and oils to do their work. Whenever the system is opened for repair, normal air gets inside. This air contains moisture along with gases that don’t work so well as a refrigerant. By using a powerful vacuum pump it is possible to remove almost all of the air and moisture from the system once repairs have been completed. If you remember from physics class liquids will transition to a gas easier as atmospheric pressure drops. Pulling a strong vacuum on the now sealed system causes any little droplets of water to vaporize so they can then be pumped out. Once that is done you are left with a nice, dry, empty place that is ready to get to work.
Which leads us to the last part, refilling the system. I won’t go into how the refrigerant works, but I will mention again that it is a sealed system. The exact same refrigerant loops the system over and over. The system is designed to work with that exact refrigerant, in an exact amount, at an exact pressure. The repair shop uses a system of pressure gauges & ports to add refrigerant (and lubricating oil) to the system. It is not as simple as just dumping in a can of refrigerant. Each system calls for a precise amount of refrigerant (measured in pounds) at a specific pressure. It is a delicate balancing act but one that means the difference between a cool A/C system and on that can keep you chilled on the hottest days of summer.
When you look at everything that went into this repair, it is easy to see that this person did not get ripped off. The parts & supplies cost alone was nearly $700, with the rest being labor and services (flush, vacuum, recharge). When faced with an unexpected costly repair bill it is easy to point the finger at the shop and scream “RIPOFF!” but when you understand the how & the why you gain some perspective. In the end my acquaintance was at peace with his bill and happy that his repair shop was still a good choice.
Photo courtesy of Morgue File