Btu Buddy 107: Heat Pump Service Call - Part 2
Now, Bob’s company has promoted him to help train a new employee, right out of a school specializing in HVAC, just like Bob was. Bob is now Tim’s Btu Buddy. Tim is anxious to travel with Bob. Tim realizes that he is right out of school, with the theory and lab work that he accomplished in school, but still needs help. He knows that he worked with many of the components of the systems in the school, under ideal conditions with good light and air conditioning. Now it is into the field, sometimes under the house with poor lighting, or out on the rooftop in the sun, where the real action is. He is naturally and normally reluctant, but he has Bob to help guide him.
Bob and Tim are continuing a service call on a heat pump that has two failed auxiliary heaters. It’s very cold outside and they have just returned from the supply house with two new heaters.
They left the heat on with the heat pump and the one remaining auxiliary heater operating so the homeowner would have some heat while they were gone. The house temperature was down to 60°F with an outside temperature of 25° with the heat pump and one strip heat operating. They left the job wondering if the heat pump itself was operating up to capacity.
When they got back to the house with the new heaters, they went to the indoor unit and shut it down and replaced the two defective heaters and turned the system back on. They checked the amperage to the two new heaters and they were operating. Tim then asked, “What’s next?”
Bob said, “Let’s go to the heat pump for a visual inspection first to see what we see.”
They went outside and Tim said, “Wow, that heat pump is iced up. Ice is covering the whole coil.”
Bob said, “Look at that unit closely. There are weeds growing through the grille guard into the coil. When the normal ice pattern forms on that coil, the weeds will interfere with the defrost cycle. That unit is a mess. It’s a wonder it is heating at all.”
Tim asked, “What can we do to get that ice off of the coil?”
Bob responded, “It would take many forced defrost cycles and a lot of time to get the ice off using the unit’s defrost cycles. We have a great external heat source for removing the ice right here. The city water temperature is about 45° and it will be great for the removing the ice. Remember, this is not block ice. It is not a dense ice. It has a lot of air in it.”
Tim asked, “What do we do next?”
Bob said, “Before you do anything, use your cell phone and take some pictures of this coil. Then turn the power off and take the top off of the unit. It contains the fan and we can set it aside without removing the wiring. The wires are long enough. Then cover the control box with plastic to keep it dry.”
Tim did this and then Bob said, “Get the water hose from the truck and connect it to this hose bib on the side of the house and set the hose to a spray and wash the ice off of the unit. It will take maybe 20 minutes.”
After Tim cleared the ice from the unit, Bob said, “We have to remove the weeds from the coil. I believe we will have to remove the coil guard to do a good job. Take a few more pictures showing those weeds in the coil.”
They removed the coil guard and pulled the weeds from the coil by hand and put the coil guard back on, and Bob said, “Boy, it is cold out here, but I believe that we need to apply some coil cleaner to the coil and then back wash it with this water hose. I hate to do this in this weather, but we are here and have the unit set up for a coil cleaning.”
Tim asked, “What do you mean by back wash?”
Bob explained, “The airflow is towards the center of the coil because the fan pulls the air in and discharges it through the top of the unit (Figure 1). This means that any dust or dirt will be in contact with the outside of the coil first. To back wash, we will apply the water to the inside of the coil and force the dirt to the outside of the coil. We’ll spray the coil with coil cleaner and get it soaked. This will help remove the dirt from the coil.”
Tim said, “I get it. If we wash the coil from the outside inward, we may force any dirt on the outside of the coil to the inside of the coil. We probably wouldn’t get the coil as clean.”
They cleaned the coil and Tim said, “I just thought of this. We shut down the unit and have had the heat off in the house. I bet it is getting cold in there.”
Bob said, “Where is the power supply for the low voltage?”
Tim said, “I didn’t think of that. It is in the air handler. The house has had the strip heat operating, so it shouldn’t be too bad.”
When they finished cleaning the coil, they put the unit back together, turned the power on, and the unit started running. Tim asked, “Should we do a performance check on the unit?”
Bob said, “To do a full performance check, we would have to put gauges on the unit and take wet and dry bulb readings. I think that we will do a simple check on the system. We can measure the discharge air temperature of the air leaving the heat pump, without the electric heat coils. If the air temperature is about 95°, we can declare the unit good to go.
“On this unit, we can disconnect the electric heat by removing the W1 wire in the air handler (Figure 2), and insert a thermometer probe in the air stream and we will record only the heat pump discharge air temperature to see if it is really heating. Let’s place the thermometer lead in the first air discharge register, which is in the dining room.
“We can also observe the outdoor unit frost pattern to see if it has enough refrigerant charge. If there is enough refrigerant, the coil will be iced to the top of the unit.”
After the unit had been running for about 20 minutes they observed the temperature in the dining room air register to be 96°. Then they looked at the outdoor unit and the frost line on the coil was very near the top of the coil. Bob said, “From a visual observation, this unit is doing well. Let’s show these pictures to the homeowner. Take another photo of the cleaned unit for comparison.”
They reconnected the strip heat. Then they showed the photos to the homeowner and she had them email them to her email address so she could show her husband.
Tim said, “Well, that was an interesting service call. The picture of before and after to the homeowner was a great idea. She could see the evidence and that verifies the value of a service call well done to the customer.”
Bob said, “Doing a good job and proving it to the customer is always good. They want good value for what they pay, just like we do.”
Publication date: 02/20/2012