Steve Miles is the general manager of Jerry Kelly Heating and Air Conditioning in St. Louis. He has seen his share of misdiagnosed unitary air conditioners and heat pumps — the company offers free second opinions for potential customers who have already had their systems checked by other contractors.

Many system misdiagnoses, he agrees, unduly condemn the compressor. If it’s under warranty, the replaced compressor may undergo a teardown to find the cause of the failure. When no failure is found — the compressor would work if put into another system — manufacturers such as Copeland Corp. (an Emerson Climate Technologies company) give it a tag reading “No Defect Found” (NDF).

According to that manufacturer, approximately 30 percent of all air conditioning and refrigeration compressors returned to them under warranty are NDF units.

“Understanding is the key to correct diagnosis,” said Miles. This includes understanding electrical wiring, diagrams, and safeties that may trip the compressor off.

Rookie Errors

The most common compressor misdiagnoses Miles has seen include:

  • Condemning the compressor because the terminals are burned off. “As long as there’s anything left of the old terminal, this can be repaired,” Miles said. The problem itself is caused by loose connections and arcing.

  • Condemning a locked-up compressor. Instead of using a start-boost kit to see if it might start, the compressor is condemned. Miles said the locking could be due to tight bearings (normal wear and tear), too much back pressure, or unequal pressures in general.

  • Condemning a compressor that has stopped operating due to open overloads (thermal overload). Most residential compressors reset once they cool down sufficiently, Miles said. They generally overheat because the system ran low on refrigerant or due to poor maintenance (e.g., dirt caked on coils), he explained.

    In general, there is “more misdiagnosing than there should be,” he said. “Of all the second opinions we are called for, half of the compressors we see have no problem.”

    He hasn’t been to a Copeland teardown yet, but is very much interested in them. In-house training at Jerry Kelly Heating and A/C comes mainly from weekly service meetings, which Miles calls “training du jour” because they cover problems creeping up in the field that week.

    A lot of the training is designed to remind technicians of the basics, he said. “Every time the season changes, we need to review the basics.”

    The company will be installing the Copeland “Comfort Alert,” an onboard diagnostics system, on unitary systems for preferred service agreement customers. Miles believes that this will lend still more credibility to their diagnoses.

    Old, Expensive Problem

    According to Scott Barbour, executive vice president with the manufacturer, “I’ve been at Cope-land 11 years and [the NDF problem] has been here as long as I have and before.” It has consistently been on about one-third of all warranty returns, and is caused mainly by the parts-changer mentality, Barbour said.

    “Sometimes compressors are replaced because the service person detected noise — it might be due to vibration — and they pull the compressor,” he said. Or, the problem might be other controls in the system that prevent the compressor from starting. For one memorable system that went through several consecutive compressors, the problem actually was a stuck expansion valve.

    It’s a huge expense for manufacturers, he said, which includes not only the warranty but also shipping.

    What if NDF returns were reduced by half? For example, Barbour said, an original equipment manufacturer could reduce internal processing costs. The money could be applied elsewhere — R&D, contractor programs, the bottom line, and the cost of products. “If you could decrease your warranty costs, you could offer something like Comfort Alert at no additional cost,” he said.

    Contractors would see the benefits of solving problems right the first time, as well as making sure new systems are installed correctly. “A contractor’s reputation is the best asset he has,” said Barbour.


    The diagnostic is accessed by the contractor or technician at the condensing unit, where a diagnostic code tells the person what the system problems are (see Tables 1 and 2).

    With that information, “The technician is directed to the root cause of the problem,” said Copeland’s Residential Marketing Manager John Schneider. It helps them get to the true cause faster, and therefore can improve productivity as well as accuracy.

    For the homeowner, Schneider said, it offers better quality service. “They can be more confident of the contractor’s diagnosis.”

    That brings up the issue of credibility. With all of the HVAC contractor stings that have been televised, contractors can use the tool to support their recommendations to skeptical homeowners.

    The system is being tested for wiring to a White-Rodgers thermostat, where a flashing light can make the need for service visible to the homeowner — “like a check engine light in the car,” said Schneider. Information from Comfort Alert is tracked in the system over time; if system problems are detected, the control sends a series of flashing codes. An advanced troubleshooting guide that accompanies the system was developed with feedback from Copeland engineers and service schools.

    Future developments for the technology might include an interface with contractors’ offices, Barbour and Schneider indicated. The system has been accepted by Lennox and Nordyne for their top lines.

    Table 1. With Comfort Alert, a diagnostic code tells the technician what the system problems are. This feature can help the technician get to the true cause faster, and therefore can improve his productivity as well as accuracy.

    Table 2. Using a troubleshooting guide, technicians can determine which areas they should look at specifically. For example, Yellow "Alert" Flash Code 3 indicates that the compressor is running only briefly.

    RETS Tested

    The company knew it was onto something when the product was tested by HVAC students at a RETS Institute of Technology school.

    Various failure modes were set up for the HVAC students to troubleshoot. Their accuracy without Comfort Alert was 17 percent, Schneider said. With Comfort Alert it improved to 92 percent. “With guys from the field, there was 63 percent accuracy without Comfort Alert,” he continued. “With Comfort Alert, it improved to 100 percent.” These figures are consistent with Copeland’s 30 percent NDF return rate.

    “That was an eye-opener for us,” Barbour said.

    Could the insidious NDF problem finally start to decline? That remains to be seen, but the indicators are good. More importantly, the outlook is bright for improved consumer trust.

    “I think this is a way to sell peace of mind,” Barbour said.

    Publication date: 05/19/2003