Before we get started, you need an EPA 608 (commercial, residential and marine systems) or 609 (automotive) license to purchase refrigerant and/or work on an air condioning system with the exception of 134a cans less than 2 pounds, working on an automotive air conditioner, not for pay. That said the penalties for intentionally venting refrigerant into the atmosphere is a federal offense for everybody, that carries up to a $38k fine per day per incident and potentially criminal prosecution of up to 5 years or more in prison. There are numerous examples of criminal prosection. So while we are here to learn about our air conditioners and how to repair them, be aware of the law.

With that out of the way, lets get to work.

The refrigerant circuit of an AC system is a closed system, it rarely needs to be opened to the atmosphere. If it does, this is much more serious air conditioning work and it has to be done right for a durable trouble free repair. Reasons why this level of repair may be necessary:

1. A leak needs to be repaired
2. The compressor has failed
3. There is an internal system blockage such as at the orifice metering device
4. There is too much oil in the system
5. The system was contaminated

Leaks:

Leaks are common in older automotive AC systems. O rings dry out, componets get loose, components start leaking. A leak can be found in virtually any part of the system: compressor (belly band), hoses, connectors, condensor, evaporator, etc/ The best way to determine if you have a leak and to find its location is to pressurize the system with dry nitrogen to at least 150 psi (do not exceed the high side operating pressure) and watch a pressure gauge on either port for an hour and see if the pressure drops more than a few psi. If it does then examine all of the potential leak points for dirty oil residue, it leaks out with the refrigerant. If that doesnt do it, start spraying all the possible leak points with soapy water and look for bubbles. If that doesnt do it then you add a small amount of refrigerant and spark up a leak detector. I can tell you that unless the leak is massive, a leak detector can be frustrating and takes time to master. Do not just keep filling up a system with a large leak with refrigerant and letting it vent to the atmosphere.

Compressor has failed:

Sometimes the clutch goes out, the compressor valves get weak or a valve reed breaks and those failures are less involved. If on the other hand you have a compressor that overheats and implodes then the debri in the sustem has to be dealt with and the system has to be opened up and flushed or components replaced. This is less of a problem than say in residential units where an electric motor in in the compressor and you can get a burnout. The most obvious sign is trash at the orifice metering device. A full set of gauges helps you here, especialyy to identify weak valves.

Internal blockage:

You need a full gauge set to spot this, usually the high side pressure is too high and the low side too low and cooling suffers.

Too much oil:

The low side switch can act funky, the compressor can start making knocking noises. More is not better here.

Contamination:

The most common cause here is lousy charging hygiene or a badly conducted system repair. Moistures gets in the system or incompatible oils get mixed and gunk forms. You usually see gooy blobs at the clogged metering device. In this case components will need to be flushed or replaced. RX11 is a common flush that is compartible with refrigerant oils if some residue remains.

If the system needs to be opened then the refrigerant first needs to be reclaimed with a machine and storage container. Then the components get replaced, all o rings involved get replaced, a new orifice metering device get installed with a new compressor and you always replace the accumulator. Make that the last thing that you open and install so that the descicant does not get exposed to excessive humidity. Then you pressurize the system to around 150 psi with dry nitrogen and see if it holds for an hour. If so then you connect a vacuum pump and micron gauge to the system and vacuum until you are below 500 microns and preferably below 350 microns. The amount of time that this takes depends on your pump, hose quality and the condition of the system. This process removes non-condensables (air and humidity). As the pressure drops then the water in the system goes into vapor form for removal. IOW it lowers the boiling point of the liquid water. If the system was a mess to start with this can take hours. You can speed it up by breaking the vacuum with dry nitrogen up to 3 times (triple vacuum). Once you are at 350 microns you blank off the system and make sure that it holds at least 500 microns after 30 minutes. Then you break the vacumm with 134a and weigh in the plate charge with a bottle of gas and a scale. If thats not available then charge to the target pressures and center vent temp. More charge is not better after this point.

System oil:

One of the most confusing areas of AC repair is the refrigernt oil. 134a systems use PAG oil with a viscocity appropriate for that compressor. When you replace a compressor use the oil that came with the new compressor. If the compressor is dry use the viscocity that the compressor mnfg states. Pour the oil out of the old compressor and measure it. Pour th oil out of the new compressor and return only the amount you measured from the old compressor. The system oil (around 8 ounces for these systems) is distributed throughout the system. If you replace any componets (evap/condensor/hoses) then its about an ounce per component. Treat the accumulator like the compressor, measure and replace the old oil amount. If you flushed the whole system then you will need closer to the 8 ounce total. Rotate the compressor by hand multiple times .before start up.

Most shade tree mechanics do not have all the gear for a full repair. A potential approach would be:

1. Shop or buddy removes the refrigernt
2. You do the repair
3. Shop or buddy leak tests, vacuums and weighs in the charge

Do not just do a repair and then sweep the system with refrigerant, charge it and call it good. First its illegal but second that system is contaminated and will have reduced service life. I had a debate hear years ago with a member who claimed this approached worked fine. He came back later and reported the failure of the system admitting that maybe that approach wasn't the best route.


George