Playing in Tune: Proper Use of Diagnostic Instruments

Correct application and use of diagnostic instruments are essential for harmony between you and your refrigeration customers. As a business owner or service manager, you want to be confident that your technicians are using tools correctly, and are aware of all the tips and tricks that make field service a melodious experience.

“At Fieldpiece, one of our goals is to provide ways to allow service technicians to diagnose HVACR
systems faster and easier, but also correctly, says Russ Harju, product manager for Fieldpiece Instruments.

Refrigerant Recovery Tips
Harju says the level of vacuum required for complete refrigerant recovery is one of the most common misconceptions technicians have.

“Refrigerant recovery involves taking refrigerant from one spot and putting it into another spot, and it’s pretty obvious at the time if it’s working or not," he says. "Once all the refrigerant is out, you have to pull the system into a vacuum to remove all the moisture, air and anything else that might be left.  

“One of biggest misconceptions involved with refrigerant recovery, is how low you have to run it, and how long it needs to stay there.Technicians tend to have the hose on for too short or too long a time. Either way, problems can arise."

As you'd expect, Harju says the best way to determine the correct amount of time is to follow manufacturing recommendations.

"They generally tell you to pull the system down to 500 microns, and properly valve-off the system to completely isolate it. Proper set up and tight connections are key.  Once it’s down to 500 microns, and the system’s properly isolated into a vacuum, you want to make sure it’s under 1000 microns for about five minutes. If it stays under that, it’s not leaking. A lot of guys think that because it’s leaking a little bit —500 to 1000 microns, they have to make repeated attempts. So, they’ll tend to do it over and over again, but they’re not making the system any better. They become frustrated that it doesn’t hold perfectly at 500 microns indefinitely. Microns are super-hard to hold. A micron is basically a negative pressure reading, and one micron is equivalent to .00002 psi."

Leak Detection Tips
When it comes to leak detection, Harju believes a detector with a heated diode can work as well as the modern infrared detector, however the diode can become less sensitive over time, and should be replaced at least every three years.

The infrared detector never degrades, but technicians should remember to change the filters about once a month.

Harju says the key to performing leak checks is to cover all the usual places where leaks occur, and move the detector slowly enough so that it can find leaks.

Digital Manifold Benefits
Digital manifolds are the new trend, and Harju says their biggest advantage is in providing a greater number of measurements and live calculations.

“An analog set has basically two pressure sensors and three or four hoses, depending on the type of manifold,” he explains. “With an analog set, you have to record those two pressures, convert them to saturation temps using a P/T chart, and subtract that from the line temps you measured to get your superheat and subcooling. Then, compare them to the target superheat or subcooling. A digital manifolds read two pressures, performs the pressure/temperature calculations and automatically calculates superheat and subcooling. It’s nice to see, when you’re adding or removing refrigerant how it affects superheat and subcooling second by second. Then, you can watch it stabilize, rather than doing multiple calculations very few minutes," Harju says.

According to Harju, an advantage to some of today’s digital manifolds is that they take air temperature into consideration.

"You put sensors inside the ducts, and they send indoor wet blub and air temperatures outside while you’re charging the condenser. Everything is displayed live on one screen. They can toggle back and forth between 'Superheat' and 'Subcooling' mode to 'Target Superheat' mode, so when they add or remove refrigerant they can see what’s happening to indoor temperatures, which are indicators of airflow. They can get a snapshot of the system quickly, without going inside multiple times.”

Harju says that even if a technician knows the basics of all the key instruments available in 2013, refrigerants, equipment, and technology changes every year, so technicians need to keep up.

“Local distributors put on lots of classes about new the new equipment out there. Classes are a great way to learn about the new equipment and catch up on the new technology and  by default becomes a type of refresher for what you know about the older technology.”

The Fieldpiece Products Channel can be found on YouTube, at youtube.com/fieldpieceproducts.

Don't Accept Guesswork

Ron Plasek, business development manager for Yellow Jacket, says it’s always in the interest of the technician and the customer to have instruments that take the guesswork out of HVACR system diagnostics.

“Today’s tools have extra features built into them, and if technicians read the manual and use the tool the way it was designed to be used, they’ll get the job done right the first time, in less time,” Plasek says.

“Shortcuts don’t help. If you buy a tool with many features, use them; read the manual, and manufacturer service resources. It’s in the best interest of everyone to use tools correctly. Fewer callbacks save money.”

Here are Plasek’s tips when using a variety of electronic tools.

Refrigerant recovery units. If the recovery unit has an inlet filter, check it occasionally.  A blocked inlet filter can slow down your recovery significantly.  If a system is not reaching a vacuum during recovery, close the path to the recovery machine.  If the machine does not pull into a vacuum when it is isolated from the system, the recovery machine is not performing properly.

Leak detection meters. Have a good understanding of how your leak detector works. Many electronic leak detectors on the market today have an auto-zeroing feature, meaning that they only alarm when they detect an INCREASE in refrigerant concentration.  If an auto-zeroing leak detector is held stationary over a leak, the alarm will go away after a short period of time.

Airflow around a leak will interfere with leak detection, blowing the leaking refrigerant away before it can be detected. Shut down fans and air handlers when trying to find leaks.

Some leaks will only appear under higher system pressures. Make sure the system contains enough refrigerant to pressurize the leaks, and run the system in the mode that creates the highest pressure conditions in the area you are checking (for example, hot gas defrost mode for an evaporator).

Micron gauges. Keep the sensors clean. Oil contamination is the most common problem, and will typically cause the micron reading to be higher than the actual value.  This can result in wasted time trying to reach the desired vacuum level or trying to find a leak that doesn’t exist.  Keep the sensor away from oil sources, wait until the system is in a slight vacuum before connecting the sensor, and break the system vacuum slowly if the sensor is connected.  Remove the sensor as soon as the system is at a positive pressure.

Multimeters. Safety first! Make sure the meter has a voltage safety rating to match your application, and always inspect the probe and lead insulation for damage.

Manifolds/hoses. Gauge accuracy is key. Gauge accuracy is rated as a percentage of full scale.  A 1% gauge will give you better accuracy than a 3-2-3% gauge.  Using a gauge with a higher fullscale range than needed also will affect accuracy (for example, using an 800psi gauge on an R-134a system). Pressure accuracy is also important.

A series of Yellow Jacket training videos can be found at yellowjacket.com/trainingvideos

Other Challenging Procedures

Measuring a pipe temperature for superheat or subcooling. Ron Plasek says having a good pipe temperature probe is just as important as having a good thermometer.  A pipe temperature probe with too much mass will respond slowly and will always lag behind the actual pipe temperature.  A pipe temperature probe that makes poor contact with the pipe or is not well insulated will be affected by the ambient temperature.  This is especially a problem when trying to measure a cold pipe on a hot day.  Look for a pipe temperature probe that has a fast response time and a low ambient temperature effect.

Electronic instruments in general. Pay attention to low battery indicators and change or recharge your batteries.  Accuracy on some electronic instruments can degrade significantly when operating in a low battery condition. The accuracy of some instruments is affected by significant ambient temperature changes.  For example, moving an instrument from a hot outdoor temperature to a cold walk-in freezer (or vice versa).  When going from cold to hot/humid, condensation can also cause problems.

Electronic scales. Plasek's advice here is similar to that with gauges. Using a scale that has a much higher capacity than you need will cost you accuracy (for example, using a 220lb capacity scale for weighing in a small charge).

Refrigeration Contractor Knows Value of Electrical Smarts,
Efficient Leak Detection

With the increasing amount of electronic controls in refrigeration systems, the technician needs to know how to work with electricity to identify and solve issues. Control circuits tend to be areas where technicians seem to be most challenged initially, says Steve Martin, Commercial Technical Manager of Carlson & Stewart Refrigeration, Marshall, MN. But once the evaluating procedure is firmly understood, it’s smooth sailing.
 
“When technicians are looking at electrical ladder diagrams, it’s important that they know where to place the probes; this is crucial for them to get through a diagnosis quickly,” Martin says. “To do this, the technician needs to initially check across the rung of the ladder to see if they have the expected voltage available for the load on that rung. With the proper voltage available, they need to check the voltage at the middle relative to both sides of control circuit to determine which side of the circuit requires additional trouble shooting. Repeating this procedure on the side of the control circuit that is not working will quickly get the technician on to the failure. “

“Working with electricity requires understanding and awareness of visual cues (meter readings, mechanical switch contacts, indicator lamps, etc.) to properly define the health of the system.”

Martin says proper refrigerant leak detection is of utmost importance, especially when customers’ stores are often located hours from the CSR main office.
 
“We’re in a rural area, and often our customers aren’t going to own the technology to monitor leaks in their refrigeration systems. CSR technicians walk the entire store to identify potential leaks, and eliminate them before they start to get expensive,” Martin says.
 
“We’re currently using the electronic H10PM by Bacharach. It’s a sensitive tool, and technicians can’t let the sensor probe linger at the leak site. This will cause the sensor to wear out sooner. They’re instructed to remove the detector off from the area of the leak as soon as its detected and use a visual indicator (they use Big Blu liquid), so as to not destroy the integrity of the tool and to positively identify where the leak is”
 
“The leak detector is sensitive enough that we have found leaks in overhead piping in grocery stores by detecting heavier concentrations of the refrigerant in an area. It’s important to cover the entire sales floor under any overhead piping. The refrigerant is heavier than air and will drift down to floor level. Once you think you’re in the general region of an overhead leak, you need to go to the overhead piping, and scout up and down the pipes in that general area to find the leak.”
 
To detect leaks in cases, technicians check the supply air stream of the cases. This can be done fairly quickly. Once they pick up traces of refrigerant in a case, they’ll most likely have to remove product from the case to get to the evaporators and pinpoint the leak.