Air Conditioning System - Keeping Your Cool

Troubleshooting
Whether you have a new system or are working with an existing factory system, there are a few common problems that will cause it to not work to its full capacity, or even at all. "The number one problem we find is improper charging of the system or that it hasn't been evacuated correctly prior to charging," Rick said. "134a is very charge sensitive, so when Vintage Air says it should be charged at 1.8 lbs, we mean exactly 1.8 lbs." Rick also recommended using a professional charging station to charge your A/C system. Another common problem is lack of airflow across the condenser or mounting it incorrectly. "We see condensers mounted sideways or upside down. They're designed to work a specific way, and as they see a change in the refrigerant from gas to liquid as it passes through, if it's upside down or sideways, the heavier liquid can't exit the condenser!"

There are a number of typical problems that can cause a system to not cool, or appear to not cool. Inadequate airflow to the condenser can cause abnormally high pressure. The condenser should be mounted in front of the radiator, with an air gap of roughly 3/16-inch. Inadequate condenser capacity will cause the same symptoms, and running cold water over the condenser while a fan is placed in front of it will show this up if the pressure drops during the test. A useful tip here is that a parallel-flow condenser has 25 percent more capacity than a tube and fin item of the same size.

The evaporator may freeze up, either internally or externally, giving the illusion that the system is not working. Internal freezing occurs when there is moisture in the system, and will cause the pressure to drop in the low side, eventually going to vacuum. The system should be checked, evacuated, and recharged by a professional if this occurs. External freezing happens when the condensation on the fins cannot be displaced quickly enough and turns to ice, restricting airflow. Backing off the thermostat slightly from maximum should cure this, though presence of humidity in the interior can be a cause, which is why insulation and well-fitting door and window seals are important. Expansion valve failure and low refrigerant levels will also cause less-than-perfect operation. We asked Rick what causes low refrigerant levels and why systems require recharging periodically. "There will be some degradation of the charge over time as refrigerant is lost, despite it being a closed system. 134a molecules are so small they will escape, and the OEMs are doing all they can to ensure their systems retain charge," he said. "An interesting observation is that cars that see more use tend to lose less refrigerant than those that sit for long periods."

Retrofitting for R-134a
As mentioned at the head of this article, R-12 has been replaced as the preferred refrigerant of choice owing to its ozone-unfriendly properties, but what can you do if your A/C system that's been in use for years using R-12 now requires recharging? Though expensive, you can have it recharged with R-12, but the supply will eventually run dry, and the system will require retrofitting to use R-134a.

This will mean some work, and some component replacement. The system will need to be flushed to remove all traces of R-12, as mixing the two is definitely not a good move, and the oil in the compressor will need to be changed. R-12 systems use mineral oil and R-134a systems in OE applications use PAG oils. Modern synthetic oils work well in retrofit cases, as it is compatible with mineral oil as well as R-134a. The compressor cannot be flushed, nor can the accumulator or dryer, as the desiccants will be ruined. The accumulator or dryer should be replaced anyway since the desiccants in new replacements will be compatible with R-134a. Flushing the system will remove any mineral oil and other contaminants, and if a component such as the compressor or evaporator has failed, the system should be thoroughly flushed as a matter of course.

You may also want to swap out your old condenser for one of a newer design if it's the old tube and fin type (pre-1980), as R-134a will benefit from the serpentine design, or a parallel flow. Vintage Air's Parallel Super Flow is one such design.

As higher pressures will be the norm with R-134a, a useful addition will be a high-pressure cutout switch, which will not allow the compressor to cut in if the system loses charge, and will also switch the compressor off if pressure builds to excessive levels. Vintage Air markets a version of this called a Trinary Switch, which is not only a high- and low-pressure compressor cutoff switch, but also a preset pressure switch for the electric fan relay. Apparently, miss-wiring the switch for the fan relay is a common problem, and the company provides a wiring diagram to eliminate this. In fact, the company's Web site includes a number of very informative downloads.

Retrofit adapters should be installed on the high- and low-side service ports for two reasons. They allow R-134a gauges to be attached for charging and testing and instantly inform any technician in the future that the system has been retrofitted to R-134a. You may also want to label the system near the service ports, informing of the retrofit. As R-134a molecules are smaller than those in R-12, systems using the new refrigerant require O-ring fittings and all barrier hoses should have bead lock crimp connections, not clamps of any type.