WHEELER ON HVACR: A Good Vacuum Gage
A sad fact of this business is that many critical (and expensive tools) are seldom found on HVACR service trucks, and if they are, they are seldom used. Take for example, the vacuum gage. Sure, your company sells them, but how many service technicians have them, and how often do you suppose they actually get used? You know the sales, so I suspect that you have some idea of what I’m talking about. They are infrequent sales items.
What are vacuum gages used for? They are absolutely necessary whenever a service technician pulls a vacuum on a cooling or refrigeration system. And when should they pull a vacuum on a system? Whenever there is a major loss of refrigerant charge (for servicing reasons, or whenever a refrigerant leak is the source of the problem). In other words, a deep vacuum should be pulled and checked with a good vacuum gage on about one out of every three service calls. Do you think that is what’s happening? In a pig’s eye!
The question you might have, and it’s the same question that service technicians have, is: Why do they need to use an expensive ($100-$200) vacuum gage when they can simply use their manifold service gages? After all, don’t the gages also read a vacuum? Yes, they do...BUT!
Take a look at the small vacuum portion of a typical low-side gage. By looking, you will notice that the negative-pressure side of the gage is merely a rough estimate. In fact, you will see that the gages don’t even stay properly zeroed.
How accurate does a proper vacuum have to be? Well, take a look at those gages again and try to find 29.94 inches of mercury (that’s approximately -14.697 psig, depending on your local altitude above sea level and the weather conditions).
Why is such accuracy - and such a deep vacuum - required? Well, understand that pulling a vacuum on a cooling system serves two functions. First, it removes the air from the system, and doing that causes the system to operate far more efficiently. You see, when there is air in a system, it tends to take up space in the condenser coil, which means that the coil size is reduced and less heat is removed, which means less cooling and higher electric bills.
Bubbles of air also circulate through the system, displacing the refrigerant and doing no cooling. So, it is the best idea to remove all the air that is possible from a cooling system, because nobody wants less cooling for higher electrical costs.
The second thing that a deep vacuum does is remove moisture from the system. Moisture enters a system with the air whenever there is a refrigerant loss or leak, and this moisture ends up in the compressor oil, where it reduces bearing lubrication and tries to short out the compressor motor windings. Another very bad thing.
Something that you may not realize is that, when you pull a deep-enough vacuum for a long-enough period of time, you can get any moisture that is in the oil to boil away. You see, water boils at a lower temperature under deep-vacuum conditions. And how can you tell when the oil is dry? By using an electronic vacuum gage. When all the moisture is gone, the pressure on the gage drops (to about 10 microns). And that is why a good vacuum gage is required. Anything less is simply sloppy work that puts the customer’s compressor at risk.
Let me ask, which does your company sell more of, vacuum gages or compressors?
Of course, other service components have to be in top shape also, in order to reach a deep vacuum. Take, for example, the vacuum pump. Not only must a vacuum pump have two stages and be in good operating condition, the pump oil must also be changed after every two or three vacuums, to keep it from becoming contaminated. What do you figure that comes to, about once every day? How much vacuum-pump oil does your company sell?
Then there is the condition of the manifold gages, and especially the refrigerant hoses. Standard rubber hose sets have to be kept in top condition to be able to pull a deep vacuum without leaking or collapsing. In fact, it is better to use special metal-braided hoses for a vacuum, because they won’t leak or collapse.
Then there is the matter of how to break the vacuum with a refrigerant charge and not contaminate the clean system with air and moisture in the process. Think about how you would accomplish that with a standard two-knob manifold-gage set and a vacuum gage that isn’t built into the manifold...almost impossible! I prefer the type of vacuum gage that is built into a four-knob manifold (one for the low side, one for the high side, one for the refrigerant drum and one for the vacuum pump), and which reads a vacuum with LED indicators. But, how many of those do you sell?
I read of the coming phaseout of HCFCs and of how the future lubricants that are used with HFC refrigerants must have special handling and service techniques to prevent their being damaged by airborne moisture. And then I take a look at the current state of our industry and its lack of proper tools and procedures, and cringe.
Anyhow, take special note of those technicians and companies that you sell vacuum gages, four-knob manifold sets, metal-jacketed hoses and a lot of vacuum-pump oil to, because these are the people to call when you want your own air conditioners and refrigeration systems serviced. They are also the successful companies and technicians of the future in our business.