ACHRNEWS

Btu Buddy 102: Continuing the Inspection of Multiple Split-System Heat Pumps

September 19, 2011
Btu Buddy 102-Fig 1
Bob is a service technician who is well trained and nationally certified. However, he has sometimes suffered from the same confusion that all technicians occasionally do — the facts that he gathers may or may not point to the obvious cause of the problem or the best solution. But Bob has had something that no one else has. He recalled his long-time HVACR mentor and imagines him accompanying him as “Btu Buddy,” someone who reminded him to take time to stop and think before rushing to judgment, helping keep him on the right track, even with facts that are confusing.

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 on the second day of an inspection of an apartment house building that has multiple split-system heat pumps. They have given a visual inspection to all of the 60 outdoor units on the roof. They have numbered and listed all of the units with a description of all of their observations. They are now going to inspect all 60 indoor units. When finished, they will make repairs or adjustments.

They entered the first apartment to check the indoor unit of the heat pump. It happened to be the indoor unit for unit number one, the unit that was observed to have a sweating compressor. Tim opened the closet door to the indoor unit and said, “Wow, listen to that air noise. It is whistling. This is not right.”

Bob said, “Remove the fan compartment door.”

Tim tried to open the door and said, “It is very hard to move. Should I use a screwdriver to pry it open?”

Bob said, “No, shut off the breaker and try to open it again.”

Tim turned off the breaker, tried again, and said, “It is easy now. What is going on?”

Bob said, “The whistling sound was a dead giveaway to a restriction in the return air system. Either the filter, which is in a filter grille, is stopped up or some other restriction is happening. Let’s look at the return air grille.”

They had to look around to find the return air grille. When they found it, it was behind a table that had a large table cloth draping over the side. The table cloth was being pulled into the surface of the grille, partially blocking the airflow.

Tim said, “Boy, that is really a blockage. What’s next?” (See Figure 1 for examples of some typical duct blockage problems.)

Bob said, “Sometimes it is a simple fix. Let’s pull the table away from the grille and check the filter.”

The filter was in good shape and Bob then said, “Let’s write a note to the tenant to be careful and not block this grille and explain that harm can come to the system, not to mention reduced cooling capacity.”

They turned the unit back on and observed that the suction line was cool, but there were no signs of liquid in the line.

Bob said, “Now is the time to mention that if we had fastened gauges to the system, we would probably have altered the unit’s overall charge by allowing liquid to enter the high pressure gauge line. With these gauges, we could have shut off the liquid at the gauge line end and pulled the liquid back into the system (Figure 2). By doing that, we would only lose vapor pressure, which is not much, but care must be taken to purge the gauge lines and the gauge center line or contaminants can be pulled into the system. If the gauge center line is full of air, air will be pulled into the system. That is not good.”

Tim then said, “Yes, I think like you, let’s keep it simple and not create a problem where there wasn’t one. What you said sounds good, not to mention that any time you fool with a gauge port, you invite the possibility of a leak.”

Bob and Tim moved on from one unit to another and Tim said, “I put a check mark on our check-up sheet by the units that obviously had problems and the next unit is one of them. It had frost on the suction line at the outdoor unit. It will be interesting to see what we find at the indoor unit.”

When they opened the closet door to the indoor unit, it was obvious there was a problem.

Tim said, “The suction line is frosted up. This unit has problems.”

Bob said, “Do a visual inspection and see what you see.”

Tim looked around and said, “The liquid line is frosting before it enters the metering device. I know this is wrong, but I don’t know why.”

Bob said, “When you see a problem like this, look for the direction of the liquid refrigerant flow. Which way is it flowing?”

Tim said, “It is the summer cycle, so the liquid should be flowing toward the indoor unit.”

Bob said, “Follow the liquid line back towards the outdoor unit and see if you discover anything different.”

Tim found a stool and stood up beside the air handler where the liquid line ran into the attic. He couldn’t see anything above the ceiling.

Bob said, “Look around for an access to the attic.”

Tim looked and said, “Here is a collapsing staircase to the attic. I am going to have a look around.”

He went up and came back in just a minute and said, “Someone has moved some heavy boxes around and put a sharp bend, a kink, in the liquid line. The line is sweating after the kink, but not before the kink.”

Bob said, “Let’s just fix this one now, if we can. Turn the thermostat to the fan on position and the selector switch to off. This will allow the evaporator fan to run and melt the ice out of the coil while we see if we can repair that line without removing the refrigerant.”

Tim asked, “How can we do that?”

Bob said, “Look in the tool compartment and you will find an old flaring tool block that has two pieces; it is split in the middle. I keep if for occasions like this when working with an inline piece of tubing (Figure 3). We will see if we can squeeze some of the kink out of the tubing. We just need to squeeze it enough to get full flow. We don’t have to get the tubing back to perfectly round.”

Tim returned with the flaring block and they partially straightened the tubing out and fastened the flare block around the tubing and gently squeezed the kink almost all the way out of the tubing.

Bob then said, “There is an old 2 x 4 piece of wood. Look around and find a couple of nails and let’s fasten the wood plank next to the liquid line to protect it. That tubing probably will not take another bending at that point before it starts leaking.”

Tim said, “That was a quick comeback from a possible real problem.”

They went back to the air handler and the fan had melted the ice from the coil. They started the unit and let it run. The liquid line became warm, and the suction line became cool which was normal. The system was back to normal.

Bob said, “The 75°F room air is really great for defrosting an evaporator coil. The air is warm and there is a lot of it. Once a small amount of airflow occurs, it will melt the rest of the ice off really quickly.”

Bob then said, “We are nearly through with the visual inspections of the indoor units. We can start on the repairs tomorrow.”

Tim replied, “We have made a few very minor repairs and have several pieces of equipment running normally again, and we discovered and diagnosed the problems without instruments, just by observing. That is a great learning tool.”

Bob then said, “Keep it as simple as possible.”

Publication date: 09/19/2011