Btu Buddy 174: Under Water Condenser Repair
I created this service call to help technicians understand flooded unit repair. Dedicated to technicians after Hurricane Harvey and Hurricane Irma — I hope it helps. Good luck.
Bob and Tim traveled to Houston after Hurricane Harvey flooded thousands of HVAC units. They are part of a team to help the recovery of HVAC systems.
Bob and Tim were riding up to their first assignment to clean up a heat pump system that had been flooded in the storm. The house was a multi-story house with a concrete slab floor, which is typical of this part of the country. The water level in the house had been up to about 3 feet for several days. The storm water was freshwater, not salt water, which was a big benefit.
Tim ask an obvious question — “Is this really an economical move to try to clean up a system that has been flooded rather than buy a new system?”
“I believe that it is,” Bob said. “I think it is going to take us about three quarters of a day to complete this process and turn this flooded unit back into a workable unit. This system is supposed to be about three years old. I also question whether you could buy another system locally at this time because of availability. I believe parts and systems are going to be very hard to come by in the Houston area for some period of time. The customer is also anxious to get the cooling turned on in the house to reduce the humidity and moisture level in the structure so that they can get back to refinishing the inside of the house.”
“What are the various areas that we need to be concerned with on this system? Where do we start?” Time asked.
Bob said, “This is a split system heat pump with the evaporator inside the structure and the outdoor unit out behind the garage. Water seems to have flooded above both units, so both units will have to be repaired. This seems to be an ordinary heat pump, not a super-efficient heat pump that has variable speed motors. That will make it much more simple.
There are four areas that we will need to think about working with;
1. The unit’s cabinets or enclosures, indoors and outdoors;
2. The heat exchangers, which would be the indoor coil and the outdoor coil;
3. The system electronics and electrical; and
4. The electric motors, indoor blower motor, and outdoor unit fan motor.
Take a photo of every wiring sequence you disconnect, as well as the blower and fan motor positions in their brackets. We will take them one at the time.”
When they looked at the system, they decided that the indoor blower unit needed to be disconnected from the duct work and taken outside, so they could perform the work. The house thermostat was above the flood water line. They connected their recovery unit, recovered the refrigerant from the system, and pressurized the system up to 2 psi above atmospheric pressure with nitrogen and cut the indoor unit loose from the piping. Then they sealed the hot gas line and liquid line on the piping system and the coil and soldered them shut to protect the internal piping.
They moved the unit to the driveway and removed the coil so that they could easily pressure wash the coil inside and out. They removed the motor and electronic circuit board from the unit. Then they pressure washed the cabinet to get the silt, or muddied water residue off of the cabinet.
They lightly pressure washed the circuit board, used a solvent to help clear away the water, and then moved the circuit board to a picnic table with a black plastic cover laying in the sun. The black plastic cover would absorb sunlight and cause the top of the picnic table to be like a low temperature oven to cook the moisture out of any electronic components in the circuit board.
“I thought water would ruin a circuit board?” Time asked.
Bob said, “The circuit board components should be assembled and covered with a clear epoxy or coating that would make the circuit board components waterproof. When the circuit board dries, it should be as good as it was before the flood.
“The motor is going to be an entirely different procedure because of the bearings,” he continued. “These motors have either sealed bearings that are permanently lubricated or bearings with oil holes so that they can be lubricated during service procedures. We will discuss both types of bearings.”
They had the motor out of the blower wheel housing and onto a bench where they could work on it. Tim took the pressure washer and washed the outside of the motor, then they dried the outside of the motor.
Bob then said, “We have to be careful how we take this motor apart because it has to go back together exactly as it came apart. It is not complicated if you will follow the steps:
1. The end bells of the motor will have to come off. Scribe a mark across the end bell to the body of the motor on each, so you will know where to put the end bell back exactly to the motor body (Figure 1). Put two marks on one end and one mark on the other end so that you will remember to get the center part of the motor positioned back to the correct end bell;
2. When you have the motor properly marked to where you can put it back together, remove the four screws that run all the way through the motor; and
3. Separate the motor from the end bells, and pull the end bells off. You should now have a rotor with the shaft, a back end bell, and a front end bell (Figure 2)
The bearings on this motor are the type that need to be lubricated, so we will have to pay a very close attention to the bearings. Take a putty knife or screwdriver point, remove the metal end cap that faces the outside, and look under that protective cap. You should see a media that will hold oil — this is an oil reservoir, and the media is normally saturated with oil that gradually lubricates the shaft. Of course this motor has been underwater for a week, and the lubrication chamber is full of water and oil. Remove the media, and squeeze all of the oil and water out of it that you can. Now, lay it on paper towel to dry — we will reuse this media. You may want to rinse the media with some solvent to displace the water, then squeeze the media as dry as you can, and let it dry on the towel. Now, remove the end cap on the other end, and do the same thing.
“The motor windings are full of muddy water residue,” Bob continued. “Pressure wash the motor windings, keeping the pressure washer nozzle well back from the windings. We could even just use a water hose as we don’t want to damage the windings with a pressure washer. When you have washed the motor, use a leaf blower, and blow the windings out to remove as much loose moisture as you can. The rest will dry out rather quickly in this hot sun.”
“All of this looks very practical — it is not near as complicated as it sounds,” Tim replied. “If my child’s tricycle were flooded, I would do about the same thing — remove the filth with a pressure washer, wash out the bearings, and re-lubricate. This all makes sense.”
Tim had washed out the motor and set it up on the black plastic covered bench.
“We need to let these parts dry for maybe an hour,” Bob suggested. “This hot Texas sun will cook all the moisture out of those parts that are sitting on that black plastic tarp. While these are drying, we could move on to the outdoor unit and start getting it ready to clean up.”
They worked for about an hour disassembling the heat pump outdoor unit while the indoor unit components were drying. They got the outdoor unit apart by:
1. Removing the circuit board;
2. Removing the fan and motor; and
3. Removing the fan blade from the fan shaft.
They began reassembling the indoor unit after the components were dry. They had left the air handler housing outside in the sun, and the insulation inside the air handler walls was now dry.
They oiled the bearings in the motor and the media that they had placed back inside each end bell and put the motor back together.
“We need to check the motor and make sure that it is not grounded, get the megger from the truck,” said Bob (Figure 3).
Tim returned with the megger and asked Bob to review the purpose of the megger.
“The real name for the megger is megohmmeter, the nickname is megger,” Bob explained. “Its function is to detect a ground in the system or a short circuit from one circuit to another circuit. An ohmmeter can be used for the same function, but the megger has a much higher voltage from probe to probe and will locate a very small shortage.”
They checked the motor from the leads to the motor housing, and there was no reading on the megger, meaning there was no circuit to ground from the flooding condition. The motor was completely dry.
They replaced the motor in the blower wheel, centered the blower wheel in the housing, and tightened the hub nut to hold the fan wheel steady on the shaft.
They remounted the coil in the air handler, then remounted the fan into the indoor cabinet. Then they remounted the circuit board and connected the wiring to the circuit board. The indoor unit looked just like it came out of the box when it was new. It should still give many more years of good service.
They went into the duct work that had been attached to the air handler and shined a light to see what it looked like. It was metal duct with insulation on the outside of the duct. The inside of the duct looked good. They fastened the air handler back to the duct work. The indoor portion of the system was ready to start up after reconnecting the piping.
Bob said, “The electrician cleaned up the disconnect to the indoor unit and the disconnect to the outdoor unit. The electrical part of the system is ready to start up, let’s take the indoor unit for a test drive, and see how it functions. Turn on the disconnect to the indoor unit. Now, go to the room thermostat and turn it to ‘fan on,’ and see if the blower starts and runs.”
The blower started and sounded great.
“Well that’s a real beginning,” said Tim. “I wasn’t sure that the system would work after being underwater.”
They went back to the outdoor unit to finish the work on it. They had removed the circuit board and pressure washed it using light pressure. They had then washed it down with a solvent and set it out in the sun to dry. It was time to go to work on the fan motor.
They followed the procedures they had used on the indoor blower motor by taking the motor apart and cleaning out the bearing cavity and media that held the oil.
Bob said, “While the motor and electronics are drying out, we can reconnect the indoor coil back to the piping. Then we can come out and reconnect the outdoor unit to the piping. We must install a bi-flow drier in the liquid line; then we can pressure check the system, and evacuate the system while we’re putting the outdoor unit back together. We need to do this work efficiently because there are so many units that are going to have to be cleaned up.”
They reconnected the piping to the outdoor unit with the bi-flow filter drier, leak checked their work, and installed their vacuum pump.
The fan motor and electronics for the outdoor unit were clean and dry, so they put them back in the unit and had them ready to run. They connected the wiring and replaced the panels on the unit. They had used the megger to verify that the motor and circuits were dry. The unit was ready to start up and charge.
Tim connected gauges to the system, turned the refrigerant cylinder upside down, and allowed liquid to flow into the liquid line. When the refrigerant slowed down to a stop, he turned the cylinder over and opened the valve to the suction side of the system.
“Now set the thermostat to cool, and when you come back we will close the disconnect and start the unit,” Bob instructed.
When Tim returned, Bob closed the disconnect, and the unit started up and was running great. They used the superheat method and the subcooling method to fully charge the unit. The unit was operating just as it should.
“Go in and switch the system to heat,” Bob said to Tim. “Turn the thermostat above room temperature, so we can check and make sure the system will run in heat. We cannot run the unit in the heating mode for more than about five minutes because it’s too hot out here. The outdoor coil can absorb more heat than the indoor coil can reject, and the internal pressures will go out of sight in a minute. So, when you turn it on, come right back out because I will have to turn it off quickly.”
The system started up and was running great. The pressures were climbing when Tim walked back up.
Bob said, “Take a look at these pressures. I’m going to turn the unit off. Then you need to go back inside and s,et the thermostat for 73°F and cooling. We are going to leave this system running because the house is closed up, and I’m sure they will want to remove as much moisture from that structure as they possibly can. This unit will start pulling moisture out of the air — just watch what the condensate drain line looks like when you come back outside.”
When Tim came back outside, after just a few moments, they noticed that the condensate drain line was running a solid stream of water out to its termination point.
As they were putting their tools together, Tim ask Bob to recap what they had done that day and why. Just a short recap, so I can keep the outline in my head, he said.
“We had a flooded system,” Bob said. “There was no chance that that water could get in the refrigerant side of the system as the refrigerant pressure is much, much higher than the pressure that the water would have been under, so we just had to clean up the mess and dry out any components that were subject to electrical flow. The circuit boards voltage would not be over the nominal 240 or 120 volts to ground, so the potential for an electrical short was not really great at these lower voltages. There was very little chance that we could not get the water and dampness out of even the heart of the electrical and electronic controls. The motor bearings were actually the hardest issue we had to work with we took more time working with the two motors than we did doing anything else — except maybe the piping. It might have made more sense to put two new motors in the system, but with the numbers of service technicians in town trying to rebuild systems, I doubt if we could even buy two motors. There is, of course, a chance that this system will have a premature failure of either the electronics or motors, but I think the chances are slim, and I think we made a good decision doing what we did how we did.”
“I never cease to be amazed at how much you know about these systems,” said Tim. “Even if you don’t know it, you can figure it out as you go. You have been a great mentor to me and to the industry.”
“Thank you for that compliment,” said Bob. “That will go a long way in my life to keeping me going.”
Publication date: 9/18/2017