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Doing it right does not mean adding hours to the job. In fact, with the right tools you can do it right and save a ton of time. In this two-part series, I will discuss several ways to make your technicians faster and more productive during a typical replacement of a split system a/c unit or heat pump.
BEST PRACTICESA typical split system replacement involves several time-consuming steps, including recovery, evacuation, pressure testing, setting airflow, refrigerant charging, and performance testing. These steps in many typical installations are better described as venting, purging, setting to high speed, “close enough is good enough,” and, lest we forget, “it blows cold air.”
When it comes to saving time, nothing - and I repeat nothing - can beat the time saved by poor initial service practices. You can vent faster than you can recover, purge faster than you can evacuate, inspect for leaks faster by eye, leave the blower on its default speed rather than setting airflow, leave a factory charge alone, and verify the unit blows cold air. You can do all these things so quickly, yet they are illegal, immoral, deceitful, and just plain wrong. Sadly, these steps are practiced by a larger number of technicians than you might think, if not on all levels, at least on some.
“I don’t do it that way because it takes too long.” “You are always pushing me to get done with the job faster.” “What did you expect me to do?” These are just a few of the many excuses for not doing the job right the first time. We are at a crossroads in the HVAC industry. Simply put, the service practices we performed in the past to get the job done are not getting the job done today. Past practice and best practice do not belong in the same sentence.
A recent California study of charge and airflow revealed seven out of 10 a/c systems have incorrect airflow, and seven out of 10 systems have incorrect charge. The question is: Are your technicians finding them that way or leaving them so? Setting up a/c systems takes time. Recovery, evacuation, airflow, refrigerant charging, performance testing, and safety all take time. The old cliché “time is money” rings as true today as when it was first said. Although we cannot make more time, we can save it - and a lot of it - if we use the right tools for the job.
How do you get it done faster? Go back to the basics: Use the right tools and processes for the job. In part 1 of this article, I will cover the basics of recovery.
RECOVERY1. Use heavy duty extension cords. Any vacuum pump or recovery machine operates best between 115 and 122 volts. Lower voltages result in lower speeds and lower performance. Smaller cords have higher resistance to electrical flow and result in voltage drops. Smaller cords get hotter over time, further increasing in resistance. For evacuation and recovery machines, never use a cord smaller than 12 gauge, and preferably 10 gauge over 50 feet.
2. Use a large bore manifold. Using a large bore full flow manifold like the Appion® MegaFlow with large hose connections can drastically increase speed and reduce evacuation and recovery times. A quality vacuum-rated manifold with full ½-inch porting can provide up to 16 times the flow of a typical ¼-inch manifold.
3. Use larger hoses. A ¼-inch hose should only be used for verifying pressures and adding refrigerant. Never use ¼-inch hoses for evacuation or recovery. It takes too much time. When it comes to refrigerant removal, using a larger hose can decrease evacuation times by factors of 8 to 10. What takes a typical technician 1 hour to do with ¼-inch hoses can be done in 6 to 8 minutes with ½-inch hoses. Make sure you are using vacuum-rated hoses and connections.
4. Remove the valve cores. Schrader valve cores might be next to the single largest restriction to removing refrigerant from air conditioning and refrigeration systems. Removing the valve cores allows the liquid and vapor to flow faster. When it comes to core tools, there are differences. Core replacement tools are not rated for vacuum and typically leak when used for vacuum service. Make sure you are using vacuum-rated tools for both recovery and evacuation.
5. Remove all the liquid you can first. Getting all of the refrigerant liquid out of the system first will again significantly reduce time required for a proper recovery. It comes down to density and vapor pressure when removing refrigerant. The slowest way to remove refrigerant is in the vapor state. The lower the vapor pressure is, the longer it will take to remove the refrigerant.
6. Push-pull on systems with over 10 pounds of refrigerant. The push-pull method is useful for removing large amounts of liquid from the system. Because the refrigerant is removed in a liquid form, there are several advantages. First, because of higher density, liquid refrigerant comes out exponentially faster than vapor. When recovering vapor only, as the pressure drops in the system during evacuation, so does the temperature as the liquid flashes to vapor. The lower pressure the vapor gets, the longer it takes to recover. Removing a pound of refrigerant at 0 psig can require 5.5 times the volume compared to the same vapor at 70°F. This means that with a fixed volumetric capacity, removing the refrigerant can take up to 5.5 times longer.
7. Keep the tank cool or configure your tank to allow for cooling during vapor recovery. If your recovery tank has at least 5 pounds of refrigerant in it, the recovery machine can be used as a compressor and metering device to cool the liquid in the tank. Cooling the refrigerant in the tank reduces the pressure that the recovery machine has to work against (head pressure). This is especially helpful on hot days, and again reduces again the time required for recovery.
8. Practice proper brazing techniques. Always purge the system with dry nitrogen during installation. To do this properly, first remove the valve cores, leave the core tools attached, and wrap the service valves with a wet rag.
Work from one end and completely assemble the piping prior to doing any brazing inside or out. Purge the system with nitrogen from one side and allow the dry gas to vent out the opposite side of the system at the condenser. In other words, push from the liquid line all the way through the evaporator coil into the suction line and out the suction service valve. 1-2 psi pressure is more than adequate. There should only be enough pressure to move the flame on a lighter or match without blowing it out. Any more than that just wastes nitrogen. After brazing, isolate the system with the core tools until you are ready to perform the pressure test to avoid allowing atmosphere into the system piping.
Publication date: 01/31/2011