Unfortunately, most service techs have to buy their own hand tools, including the manifold gauges, meters, etc. And because of this, the less qualified often purchase the least expensive items, which means they can never do their jobs well.
And when it comes to manifold gauges; I wouldn’t want any service tech that arrives at my house or business with the standard old 2-knob, 3-hose configuration to work on my air-conditioning or refrigeration system. Why not? Because to do the job properly, the manifold also has to be used to pull a deep vacuum and that can’t be done well using such a tool.
Consider this: With two knobs and three hoses, you have just enough to connect to the system high-side and low-side service ports and to a refrigerant drum (for charging). So to pull a vacuum, which absolutely must be done any time the internal refrigerant lines are exposed to air; the one little center hose (which is too small and often too weak to pull a decent fast vacuum) must first be connected to the vacuum pump.
And after the vacuum is pulled, both manifold knobs must be closed and the center hose must then be disconnected and reconnected to the refrigerant drum port — and then it has to be purged with refrigerant gas (which often isn’t done) to get rid of air and moisture that is introduced by the disconnection before the system can be charged with refrigerant.
This process can be even more cumbersome when trying to do the faster “triple-evacuation” that most manufacturers recommend before starting up a new system.
Now, let’s consider how this job would be done using a 4-knob, 4-hose manifold: You connect the proper hoses to each of the service ports, one to a refrigerant drum and a larger hose to the vacuum pump. Assuming there is no pressure in the A/C or refrigeration system, you open all four manifold knobs and turn on the vacuum pump.
This allows a full vacuum to be pulled on all four hoses so as to remove any air, moisture or contaminants in them, as well as in the system that is being evacuated. Then, when a proper deep vacuum is reached, you close off the knob to the vacuum hose and turn off the vacuum pump, then open the valve on the refrigerant drum and quickly break the charge for a triple evacuation or weigh in the proper charge — no purging or reconnecting needed.
What about digital gauges? They are far more accurate than analog gauges, which lose their calibration with time. So, which would you prefer to be used when someone is charging your home A/C unit?
There also are other bells and whistles available on better, more expensive models of manifold gauges. One I especially like is a built-in vacuum gauge.
Understand that no service tech can actually determine when a proper vacuum is reached when using standard analog gauges. These (even if they were accurate) measure a vacuum in inches of water column, while a vacuum gauge measures in microns, which is the only measurement that can be used to determine whether damaging moisture is present in the system.
I encourage you to save this article. Tack it on the board or set it aside for service techs to read!