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Soon afterwards, he noticed that his relatively new 5-ton air conditioner wasn't working. He checked his thermostat; the temperature was rising and he couldn't get the system to start.
He checked the air conditioner's 60-amp breaker and found it had tripped. Snapping it back on didn't start the unit, so he called the contractor who had installed a condensing unit just a few weeks before.
The contractor, who must have been gifted with ESP, advised him over the phone to have an electrician replace the 40-year-old breaker, as it was no doubt worn out. The homeowner called an electrician and told him to replace the breaker, which he did. (He also proposed installing a whole new set of breakers, since they, too, were probably worn out. The homeowner held off on that.)
After finishing his work, the electrician confirmed that 240 V was present at the condensing unit but it still wasn't operating. He advised the homeowner to call the HVAC contractor again, collected his $250 fee, and left.
SynchronicityIt was good fortune that my son the plumber and the HVAC contractor were at the customer's house at the same time, although they weren't there together. Doug was inside and the HVAC servicer was outside, working on the condensing unit.
Doug replaced the corrugated pipe, turned the water on to check for leaks, and heard a hissing sound coming from beneath the concrete floor slab where the hot water pipe penetrated the slab.
He checked the water meter to confirm the leak; sure enough, the dial was spinning. He didn't know exactly where it was coming from, though, so he used an electronic stethoscope to pinpoint the leak; a meter shows where it peaks out. Doug said he would need to break a hole in the slab to fix the leak, and the homeowner approved the work.
After digging down about 18 inches using a temporary assistant with an electric pavement breaker, Doug discovered two copper pipes touching each other. There was a hole in each pipe where they had touched. He identified the hot water tube and spliced in a new short section. He didn't know what the other, smaller tube was for so he left it alone.
Meanwhile, the air conditioning service guy outside was checking the gas pressure - there wasn't any. He surmised that the low-pressure cutoff switch prevented the compressor from operating, to protect the compressor. He decided that he would pump down the system, recharge it, and find the leak using an electronic leak detector. He had started pumping down when he noticed something terribly wrong.
Perplexing ProblemAbout this time, Doug came outside to turn the water back on. He saw the perplexed serviceman watch as water was coming out of his vacuum pump.
He had never seen anything like this before and called his boss, who thought he was kidding, but who said he'd be right over to help solve the mystery. He'd never seen anything like it either.
Doug then called me, thinking I would like to see this strange condition. Of course I would! I arrived there with my voltohmmeter and confirmed the presence of 240 V with the compressor relay closed.
Next, after tripping the breaker, I removed the compressor's terminal cover and discovered that the ceramic terminal/seal had broken apart. This was allowing one of the terminals to contact the "grounded" compressor shell with 60 amps behind it and melting a winding lead to the motor, as well as melting away a part of the compressor shell. Now the unit became hot.
The electricity traveled through the refrigerant line, made contact through the hot water line, then went on up through the hot water pipe, up to the corrugated jumper from the copper water tube to the copper water heater - a weak spot electrically and mechanically. The tank itself was well grounded.
DiagnosisUnfortunately, the installers of the new condensing unit had forgotten to connect the green "chassis ground" to the unit's frame. The 60 amps found ground through the buried refrigerant liquid line, where it touched the hot water pipe that was connected to the hot water tank through the corrugated pipe.
The path to ground goes all the way through there, making contact with the refrigerant line and hot water line. Then the electricity found a weak electrical and mechanical connection to the tank and melted it in two.
The refrigerant gas leaked out through the hole in that pipe. Water from the water heater then leaked directly into the copper tube to the refrigerant line. When the tech ran his vacuum pump, out came water instead of refrigerant.
The tank was well grounded through the cold water supply pipes. I'm sure this sequence all happened in less than a second.
Later I learned a new, properly installed condensing unit and new liquid and suction lines were installed outside the house. I don't know how the financial part was settled. I do know that a lot of money and time could have been saved had the unit's frame been grounded properly, as required by the National Electric Code.
Donald Holzschuh, P.E., is a retired consulting engineer in Richardson, Texas. If you would like to contact him, please send an e-mail to firstname.lastname@example.org.
Publication date: 04/25/2005