HVAC ContractingTechnical

Profiting With Modern Digital Gauges

As an owner-operator, I rely on both my technical skills and my customer relationships to earn a living. My tools are essential to my work; they can be either a solid contributor or a cause of headaches. My manifold pressure gauges used to frustrate me with their poor accuracy and their difficulty to read from any distance. Now I've got a DRSA-1100 Digital Refrigeration System Analyzer. It is a powerful and convenient tool, and I can't imagine working without it.

On a typical workday, the digital analyzer saves me work time, callbacks, and helps me keep my customers happy. Follow along as I work through a typical day. You'll see how the DRSA makes me more productive and profitable, helping me make more money each year.

In this dairy tank application, the DRSA helped prevent one, possibly two, costly callbacks.

A Few Typical Jobs

On a cool fall morning, my first job was a dairy tank. It had operated perfectly all summer, but now it was cooling slowly in the cool mornings and evenings. The pressure tracking feature and fine pressure resolution of the DRSA showed me the problem was that both twin-fan condensers were running just under the initiation point of their second fans - a margin of 2-3 psi. This caused the system to run at reduced compressor efficiency and slowed its cooling. Installing aftermarket fan cycle controls the next day, I saved one, possibly two, costly callbacks and preserved a good customer relationship.

My next job was a soft serve ice cream machine, originally using R-12 but since converted to R-409A. It was fine at morning freeze down, but lost capacity when the day wore on and the demand picked up. Under load, the DRSA showed that the TEV was hunting all over the place. The pressure dynamics bar graphs told me that the TEV was throttling up and down 1 psi, resulting in a 2+ psig throttling range that alternately flooded and starved the coil. The charge on this retrofitted system is critical, so this hunting TEV would have greatly affected performance in high-load situations. I changed the TEV and drier, and ran it again reliably at high load with great recovery. Spotting both the pressure and superheat problems with any certainty would have been very difficult on analog gauges.

Table 1. DRSA vs. traditional gauges productivity comparison.

The next service call was a warranty compressor change on an R-22 rooftop A/C unit. I reclaimed the charge, changed out the compressor, leak tested, evacuated, and monitored the vacuum decay all with the DRSA-1100. I dropped the R-22 back in, verified superheat, and was off to the next service call within an hour and a half. The accuracy of the DRSA allowed me to work more quickly, with confidence that I had a tight, dry, accurately charged system. Since the warranty call pays for two and a half hours of labor, I made money on the call.

The next system I had was an R-507 ice machine. The customer said my competition had worked on it numerous times, but could not restore ice production and still charged them a lot. All seemed well, but 10 minutes into the freeze cycle, I found that the head pressure dropped, leading to the saturated condensing temperature (SCT) dropping from 90 degrees F to below 78 degrees F. That almost starved out the evaporator, as it was a capillary tube fed system. Suspecting dirt in the valve, I used two flat blade screwdrivers to spring and flush the valve out thoroughly. After resetting SCT, the cycle was stable and was 8 minutes quicker. I now had a new customer with 12-15 pieces of equipment; he was obviously satisfied as he offered to pay me right away.

A medium-sized office building that I maintained had a no-cooling complaint. The coil in the air handler was iced up. The compressors for this DX coil had older pressure controlled/operated unloader valves. With the DRSA, I found that the suction pressure was allowed to go too far down, leading to a 24 degree F saturated suction temperature (SST) on this R-22 system before the unloader would initiate; this is too cold. I managed to balance the load with the compressor operational, so I could reset and verify the pressure operated unloaders to a safe 26+ degrees F corresponding initiation pressure. I still had a very cold coil for dehumidification, but kept it from freezing up. Three-percent accurate needle gauges can't perform this 3-psi adjustment with any confidence; I count on accurate readings from the DRSA to get it right on.

A poorly performing split system heat pump had ice buildup on part of the outdoor coil. There was some oil around the plastic 1/4-inch SAE flare cap on the discharge line. I bubble-tested the cap and found it wasn't leaking at that time, but I was sure it would have been the leak on this new R-410A system. With the system in the heat mode, the DRSA quickly showed I had about 48 degrees F superheat. By moving the temperature sensor, I also saw there were 36 degrees of subcooling. With factory superheat charts in hand, I needed to correct the charge lost due to the leak. After clearing the ice on the coil, I quickly charged the system to the proper 16 degrees superheat, using the real-time reading of the DRSA. I was on my way home.

Table 2. Profitability comparison with DRSA.

Profitability Impact

It was quite a day - full of technical challenges and interesting faults. Even if your staff has less eventful days, you can expect substantial savings by using the analyzer. The DRSA can save you time in all kinds of service work. Occasionally this reduces billable time, but often the labor time savings will lead to 1/2-hour service calls, for which the minimum charge of typically one hour will apply. Your ability to handle more customers will increase profitability and more than compensate for any initial reduced billing.

Table 1 illustrates some of the work situations I described. It shows time saved by the DRSA and its impact on charges and customer satisfaction (based on $60/hour charge out). There are significant labor time savings and customer satisfaction improvements. Time saved outweighs any reduced earnings, and three unpaid hours are eliminated.

Table 2 shows the extra opportunity for profit when using the DRSA in these typical field situations. Depending on the type of equipment serviced, the DRSA can save time equivalent to doing one more week of business a year without paying for staff and expenses. How much can a technician make for you in a week?

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Using the DRSA means that your customers save money with your firm compared to your competitors. You can do the work quicker and better, fixing things reliably on the first call. Customers recognize the value of a solid firm, allowing you to charge at a higher hourly rate. The DRSA allows you to bid more aggressively for service contracts.

Increased profitability with few callbacks is a critical advantage - this is something that only state-of-the-art tools can provide in today's demanding HVACR industry. Investing in the productivity of your business is key to building customer loyalty and growing your business.

Doug Lockhart, A.Sc.T, is an HVACR contractor and founder of Digi-Cool Industries Ltd. (Duncan, British Columbia), which produces the DRSA-1100 Digital Refrigeration System Analyzer. For more information, e-mail info@digi-cool.com or visit www.digi-cool.com.

Publication date: 05/02/2005

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