"If at first we don't succeed, we'll definitely try again." This is something no customer wants to hear from a contractor, especially in the middle of July when the rooftop unit has fizzled out again. Your company is the third one out this month, and no one can seem to make the unit do anything it is supposed to do, cooling included. In spite of a good maintenance program, the unit just isn't operating efficiently. What could be the cause of all this inconvenience and expense? Improper installation.

Onboard diagnostics are slowly becoming the standard in new units. This roof mounted package also includes chillers, pumps, heat exchangers, drives, and water treatment equipment.


The first step to proper installation is load calculation. It is hard to determine the proper unit size if the contractor is unsure of the building load. Imagine a Hemi in a Kia or a lawnmower engine in a Chevy S-10.

Once the load is properly calculated and the units have been chosen, they must be placed on a firm foundation. Roof curbs and curb adapters need to be considered, along with electrical wiring and condensate drain hookup. The unit is then delivered, lifted into place, installed, and then the complete system should be tested and balanced. Maintenance contracts are signed and the customer is happy. What more could there be?

Other components to consider are integrated system controls for zoning, air management devices, economizers, and power exhaust. Then there are the fresh air energy recovery devices, filter switches, and smoke detectors to consider.

On a rooftop, safety is paramount. As with any HVAC job, it is important to consider installer safety and unit installation liability.

Every detail should be checked thoroughly. According to Ted Cherubin, product manager at Carrier Corp., one of the most common mistakes installers make is a three-phase voltage reversal. "The lack of commissioning is also a common mistake," said Cherubin. "Too often, the unit is installed and does not undergo the necessary tests to ensure integrity."


"The customer expects the installation to be a nonevent," noted Cherubin. "Once it is installed, they don't want to think about it - out of sight, out of mind."

According to him, this is a double-edged sword. "If no one is thinking about it, it's probably not causing any problems," he said. "On the other hand, however, it also makes it easier to forget about maintenance."

Maintenance is not the toughest situation a rooftop unit owner faces. The age-old repair versus replace argument can make or break an owner's budget and have a profound effect upon building comfort.

Financial constraints often push a customer towards repair, when replacement may be what is needed. As time goes on, however, the repairs usually become more costly.

"Don't wait until the system goes down," said Cherubin. "The customer will end up paying more."

Many manufacturers recommend scheduled changeouts. Not only does this help the customer budget for the future expense to come, it gives the contractor future business. Sitting down with a customer and developing a replacement schedule should be something done right after the contractor finishes going over the customer's maintenance schedule. "Having a service plan will help both parties plan ahead and be proactive," commented Cherubin.

Besides finances, customers need to consider and be reminded of occupant comfort and its relationship to increased productivity. They also need to consider new technology and refrigerant phaseouts.

As a professional contractor, it is imperative to educate the customer. Onboard diagnostics are slowly becoming a standard feature of new rooftop units. Some consider this feature a necessity, especially when remembering the out of sight, out of mind conundrum.

Onboard diagnostics are de-signed to decrease technician troubleshooting time and improve first-pass technician troubleshooting accuracy. As technology progresses, intelligent HVAC systems assist customers and contractors in their pursuit of a proactive indoor comfort approach.

Maintenance is not the toughest situation a rooftop unit owner faces. The age-old repair versus replace argument can make or break an owner’s budget and building comfort.
"Intelligent rooftop unit controllers that feature advanced diagnostic capability allow service technicians to monitor and control operation at the unit, or remotely with PC software via technologies such as phone modems or Ethernet," said Mark Hess, commercial controls product manager at Lennox Industries.

"This helps service technicians work quickly and efficiently to diagnose problems, whether they're standing in front of the unit or in their office miles away. Many issues can be fully resolved through remote access, or the technician can be better prepared when they arrive at the site."

According to Hess, the Integrated Modular Controller from Lennox used on L Series® and S-Class™ rooftop units, has more than 90 diagnostic codes available that can shorten service and maintenance times dramatically.

Refrigerant changes are another argument on the side of replace versus repair. "Green" is one of the hot HVAC buzzwords, and it is influencing almost every aspect of the industry. The government mandate that HCFC R-22 be phased out by 2010 is an event that will change the industry much the way the 13 SEER mandate changed the residential sector earlier this year.

According to Emerson Climate Technologies, R-410A, currently the primary replacement for R-22, is not a retrofit refrigerant and therefore should not be charged into systems designed for R-22. Pressures in an R-410A system are higher than those commonly seen in R-22 systems. Contractors not only need to inform customers considering repair or replacement of this information, but they also need to have service tools and gauges specifically designed to handle these higher pressures when servicing refrigerant compliant systems.

"It's important to keep in mind that in 2011, R-22 will be very expensive," said Cherubin. "For the customer's sake, contractors should start thinking about this now.

"The evolution of rooftops in general is and has been changing," he said. "Today we have higher-efficiency units, alternate refrigerants, more flexibility, and more packaged options - and the market is demanding these products."

Publication date: 06/19/2006