But the card only has values for 40 degrees and 50 degrees, so you have to take a guess. Or, do you say that the 76 psi you remember for R-22 is close enough, since you are doing a replacement with R-407C, which is supposed to match the properties of R-22 fairly closely?

In the old days of R-12, R-22, and R-502, a low-side gauge was all you needed for service. These days, we need accurate information to diagnose more subtle issues. More problems in today's refrigeration systems are within the refrigerant circuit as a result of exotic refrigerants, oils, and the possibility of toxic brews.

Traditional Bourdon tube pressure gauges and wallet cards do not give you the precision necessary to make accurate or timely decisions about what needs fixing. But there is no reason why smart tools can't solve these problems.

Digital Refrigeration System Analyzer

One such smart tool is my own invention. I call it the Digital Refrigeration System Analyzer (DRSA). It provides all the information you need and can be mounted on your charging manifold. It shows the hidden pressure fluctuations you've been missing.

It is a product that can be used with residential A/C, rooftop A/C, heat pumps, supermarket refrigeration, and low-temperature cascade systems.

Besides an accurate digital pressure reading, the DRSA has a pressure offset bar graph. The graph segments show the changes happening to low-side and high-side pressure, down to 1/4-psi movement. If a system has problems such as a little liquid flood back or a wandering TEV, such problems are easy to spot.

There is no need to carry wallet cards or make potentially fatal mistakes by miscalculating saturation temperatures.

After you select from one of the 22 programmed refrigerants, the saturated suction temperature (SST) or dew point at the current pressure is shown automatically for the low side. The high side shows your bubble point. This allows quick superheat and subcooling calculations.

For example, the actual dew point for R-407C at the old system pressure of 76 psi is 48 degrees, not 45 degrees. The analyzer tells you right on the screen when you set your pressure. You would also know that the pressure you actually want to use is 72 psi.

Don't think that's a big difference? Air conditioning systems usually get little attention for their subtle problems until they become compressor failures. And the higher failure rate of compressors is with those using R-22.

Fluorine in refrigerants - with minute amounts of moisture and air - forms HF acid, an acid that eats out glass. Since motor windings are silica-based, the motor winding insulation dies. The DRSA shows you the subtleties like liquid flood back from plugged evaporator coil, high superheat from plugged condensers, or short charges. Subtleties may be difficult to spot with a conventional gauge set.

Since it is designed to present accurate, constantly updated SSTs, the DRSA reduces charging times by allowing you to charge based on superheat.

With readings in Hg, drawing a vacuum on a system for everyday work is simple.

(However, I recommend a micron vacuum gauge when eliminating moisture or determining the tightness of a system by deep vacuum draw.)

HVACR work is much more difficult nowadays. There are many factors and many problems.

Business owners demand us to be more efficient and productive to keep their businesses up and running. We need to do so to stay in the customer's mind for future projects. Accurate, time-saving tools are an important part of that process.

Doug Lockhart is a service technician, design/build contractor, and founder of Digi-Cool Industries, which manufactures the product described in this article. For more information, contact www.digi-cool.com or 866-511-2665.

Publication date: 03/14/2005