A common request is to charge the system because it is probably "low on freon". Most of the time a check of refrigerant charge is exactly where to start the diagnostics. Here is how that process happens.
We'll roll the refrigerant recovery/recycle/recharge machine over to the car and connect the machines hoses to the proper service valves on the car.
When I open the service valves I can see the system pressures on the panel gauges. These pressures were on an actual car in for A/C service. The connections were made. The valves opened and please note the gauge readings.
Does this system need added refrigerant? I have no idea and that's my point. Have you ever seen those A/C Recharge Kits in parts stores or other stores with a can of refrigerant and a hose with a gauge? The hose will attach to the low side port of your system and the gauge reading is supposed to be how you know if the system needs a charge or is full. That is not how it works. But lets move on.
The way to find how much refrigerant is in the system is to "recover" using the machine.
There were 9.oz of refrigerant.
Refrigerant charges are based on weight. We recovered 9 ounces of refrigerant and pulled a slight vacuum on the system. A full system charge is 1.35 lb, or 21.6 oz.
The vacuum is a result of the refrigerant being drawn from the system. By allowing some time to pass (work on other things) and watching for any loss of vacuum we can get some idea of whether there is a serious leak present. We know there is a leak because the system was low. We just don't know how bad the leak is. After about a half hour the vacuum reading was unchanged. I had noticed the system had a refrigerant dye. With a dye present we can look through yellow tint glasses and use a blacklight to spot leaks.
With a light but no glasses......
Through the glasses (hence the blurry shot) you can see leaks at the seat of the pressure switch and at the bottom of the high side service valve.
There are also compressor leaks.
At this point there was a discussion with the car owner. It was decided to replace the service valve and switch. We pulled a full vacuum on the system and again allowed some time to see if it held.
The vacuum held and the system was fully charged to specs.
The system pressures with a full charge.
That is how to properly check and charge an A/C system with R134a. Those small cans and those charge kits...... just say no. On a similar note, NEVER put anything that says "leak sealer" or "stop leak" into your A/C system. At the very very best, it won't damage anything. It won't fix anything and when you do have to get the repair done it will damage my expensive recovery machine! No car manufacturer wants stop leak in the system.
There are lots of things to go wrong with A/C systems. 85% of the cars in for A/C work do have full systems but have other problems. Here I've just touched on low refrigerant and leak detection.
Hope you found it interesting. I have more and I enjoy talking shop.
Thanks for reading!
Kenneth Hayes
G&G Auto Repair
