Btu Buddy 101: Bob Trains Tim on His First Service Call
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 have arrived at Tim’s first service call.
Tim asked Bob, “What is this call all about?”
Bob said, “This is a new customer that wants us to take over the maintenance work for this apartment house. The systems are all R-22 heat pumps with electric auxiliary heat. There are 60 systems in this building, with the outdoor units on the roof. Since it is summer and the outdoor temperature is really hot, we will start on the roof for a visual examination of the outdoor units.”
When they got out on the rooftop, Tim said, “Boy, there is a lot of equipment up here. Can we handle all of this in one call?”
Bob said, “There are supposed to be 60 units that furnish the apartments; some of them are 1½-tons and some of them are 2-tons capacity. There should be a 5-ton unit that serves a lounge and meeting room area. This is an older building and it only has one power meter and the owner pays the total bill. The owner then divides the bill as best as he can and prorates it among the tenants by averaging the yearly electrical bill. This is significant because some of the tenants will not try to conserve power and some will. Individual billing is the best idea, but it is not always done that way.”
Tim commented, “We have our work cut out for us, I guess. That must be what the clipboard is for. I guess we will take it a unit at a time and make notes on the clipboard.”
Bob said, “That is right. The units are numbered on the side of the unit. There is unit number one.”
Tim asked, “Should I go ahead and fasten the gauges on it for a performance reading?”
Bob responded, “Our practice is to never fasten gauges until we first give the unit an examination using our eyes and a touch test. Tell me what you see just looking the unit over?”
Tim said, “The cabinet is in good shape. All of the screws are in it and it looks OK. There are pieces of solder on the roof around the unit. I believe it has had some sort of heavy service.”
Bob said, “Good observations. Did you feel the suction line?”
Tim reached for the suction line and touched it with his fingertips and said, “It is really cold. It sure must be cooling.”
Bob then asked, “Did you notice the puddle of water under the unit? Where do you think that came from?”
Tim said, “I would assume from the sweating suction line.”
Bob told Tim, “Take the cabinet cover to the compressor off and let’s see what we see.”
Tim removed the cover and said, “The compressor is sweating all over (Figure 1). That is not normal. How did you know what was going on inside?”
Bob said, “The suction line was sweating like it should, but when the suction line reaches the compressor, the sweat should dissipate on the side of the compressor. There should not be more than a sweat ring about the size of a donut where the suction line enters the compressor. I also checked the suction line with my hand. Did you notice that I held the line in the palm of my hand while you only used your fingertips?”
Tim said, “Yes. What is the difference?”
Bob answered, “When there is liquid in the suction line and you hold it in the palm of your hand, the liquid will conduct heat from your hand to the point that it will hurt. If there is vapor, the vapor will easily warm to your hand temperature. It will feel cool, not cold. If you only commit your fingertips, you won’t be able to notice the difference in liquid and vapor. This unit must be overcharged. We will check the filter and the indoor coil before making that decision.”
Tim asked, “How can that compressor continue to run with liquid refrigerant reaching the compressor?”
Bob explained, “When I said that liquid refrigerant is reaching the compressor, I don’t necessarily mean a pure stream, like a water hose. It is more likely a wet vapor, like a fog, with a few drops of pure liquid. The liquid will drop to the bottom of the compressor, where the oil is lubricating the moving parts. This liquid will not reach the cylinders, it will dilute the oil. This may cause oil foaming and poor lubrication for the moving parts. A compressor will often run for years under these conditions, but it will cause premature failure.”
Tim said, “That means that we can keep moving and correct the charge later?”
Bob said, “Yes.”
They then decided to record what they knew about the first unit and move on to the other units.
Bob then said to Tim, “There is a lot of sloppy work that has been done on these systems. Look at the number of empty refrigerant cylinders there are on the rooftop. It looks like there are 10 of the 25-pound cylinders just lying around. Look also at the number of compressors that are still beside the unit where they were changed out. That is bad practice because it will rain into the suction lines that are all pointed up, and eventually rain will fill them up and the oil will be displaced by the water and run out on the roof. The oil will dissolve the tar roofing. Look at that one over there. There is an oil circle on the roof.”
Tim asked, “What do we do about all of this?”
Bob said, “I am going to call the shop and get some help over here to clean up all of the junk that applies to HVAC. We are about 25 feet off the ground and there is quite a bit of work here. We will go on with our inspection.”
Bob made the call and got the clean up in motion.
They moved on to more units and Tim spotted several units that were overcharged or flooding back from other reasons. They made a note of all of them and would check the indoor units before the refrigerant recovery started.
While checking the other units, they discovered several units where the suction line was not sweating. Tim asked, “What will we do about these undercharged units. What problems will an undercharge cause?”
Bob said, “We are making notes about them and will get back to them at the end of the visual and touch inspection. The undercharged units can cause just as much trouble as the overcharged units. Undercharging a system causes it to have longer running times to cool the conditioned space. If the charge keeps dropping, the conditioned space will eventually not be cooled to the comfort level with the system running all of the time. All of these compressors are cooled by suction gas, directly or indirectly. Some compressors are discharge gas cooled, but discharge gas is a product of the suction gas temperature. If the suction gas temperature rises, the compressor will begin to overheat (Figure 2). They are overheating and running longer in an overheated condition; that’s not a good thing. True, there is overheat protection that is supposed to save the compressor, but that is not the whole story. When a compressor is running hot, the compressor discharge gas is running hotter than normal. This will cause the oil to begin to break down over time and cause problems.”
Tim then said, “You have my head whirling round and round now. I understand everything you have said. I just didn’t realize there were so many things to think about at the same time.”
Bob said, “Suppose we take a break in the details and get back to them later. We can go on and complete the rooftop inspection and then we will do the indoor unit inspection. Then we will tie them all together with the needed repairs. We are going to be at this job for a few days.”
Tim said, “I appreciate the lessons and the fact that you are willing to explain everything. I have learned the realities of liquid refrigerant in the compressor and how a low charge affects the compressor.
“We learned all of this in school, but school is much like teaching me how to ride a bicycle from a book. I really need a lot of in the field, hands-on experience. I’ll get that over time working with you. Thanks.”
Publication date: 08/22/2011