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It is the time of year when I get calls for heat pumps not cooling properly. With a little prodding, I usually hear that the past month’s electric bill was also high, even though it wasn’t that hot.
These calls always raise one major red flag for me.
The complaints usually show a leak or blockage in the heat pump coil, or a failed compressor. My first questions are if the heat pump is properly elevated up off of the pad, and if there are any obstructions around that heat pump, which could have prevented defrost condensate drainage.
Then I have the contractor look closely for distortions in the coil fins, especially along the bottom coils of the unit. If sections of the fins are distorted, more than likely there is coil damage.
Too often the issue is ice-damaged coils. These are the most misdiagnosed, yet easiest to avoid issues with heat pumps. Without understanding how this damage occurred, diagnosing it properly can be like trying to solve a mystery. Most times, by the time the technician is called out to investigate the problem, the culprit that caused it is long gone, and left no clues that it was ever there.
SLIPPERY PERPThe culprit is ice. Heat pumps are great little ice makers. And the power of ice, especially during its transformation from a liquid to a solid, is greatly underestimated.
Water is densest at 39.2°F. This is when water is the smallest it can be. As the temperature of the water drops to 32°, it becomes less dense and begins to expand slightly. When water’s heat is removed below 32°, it becomes a solid and expands 9 percent larger than when it’s in a liquid state. Few materials can withstand the pressure exerted during that expansion.
This problem can occur in many climate zones - it’s not confined to areas that are prone to heavy snow, or long days below freezing. Keep in mind that during the heating season, heat pumps are big ice makers; a rainy day in the 40s is the perfect day for heat pumps to make ice as they extract heat from that 40-ish air being pulled through the coil, dropping the temperatures to below freezing.
Low refrigerant and low outdoor airflow conditions can also cause a heat pump in above-freezing temperatures to produce quite a bit of ice. Any air reduction across the coil, or a small refrigerant loss, can build an ice monster in the most Southern regions using heat pumps.
BURSTING PIPESWe all know that water pipes will burst when water inside of them freezes. Water pipes have much thicker walls than heat pump coil tubing does.
Whenever the condensate made during defrost cycles does not drain away from the heat pump, there is a potential for ice buildup around the coil tubing. It could be that the drain openings in the heat pump are blocked, or that the heat pump is not lifted well enough off of the pad to allow for drainage.
If ice is allowed to build higher than the bottom tubing of the coil, every defrost cycle dumps all of that coil’s condensate into that ice blockage, while the heat from the bottom tube melts away about a half inch of the ice surrounding it. Eventually an ice cave is formed, enclosing the tubing, and filling with water from the next defrost cycle.
When water surrounding refrigerant tubing freezes and has nowhere to expand because it’s confined, it expands into the space available inside of that tubing, exerting thousands of pounds of pressure per square inch into the coil tube. When this crushing of the tubing occurs, it either cracks the tubing, causing a refrigerant leak, or blocks that section of tubing, causing refrigerant flow problems within the system.
Why is this issue so bad for the HVAC industry? The damage to the tubing can damage compressors and other costly equipment components. This raises the cost factor for manufacturers, who must provide warranty parts for this equipment.
Misdiagnosed units are often blamed on the manufacturer for building inferior equipment. This is most unfair, because aside from the consumer, the manufacturer is the most adversely affected by this easily avoided condition, which costs us all more, eventually.
REASONABLE PREVENTIONSolutions for this condition are far more costly than an ounce of prevention would have been. Unfortunately, that ounce of prevention is somewhat inconvenient for installers, and usually requires more labor than the install would have used otherwise.
One of the reasons for my being so excited about being able to rid the HVAC industry of this problem, though, is that it has become so much easier to prevent it.
I do blame heat pump manufacturers somewhat for the way instruction manuals are worded. I also blame anyone using the term “snow legs” for products used to separate the heat pump from the pad.
Manufacturers’ instructions usually go along the lines of; “Raise the units above the anticipated snow level.” This is ridiculous. If snow builds around a heat pump, the defrost cycle will melt away snow within an inch of the coil, which is all that is needed to keep the coil from being damaged, and actually allows the heat pump to continue doing its job.
Snow is fluffy stuff. It takes an average of 13 inches of snow to equal 1 inch of water. So when a manufacturer instructs us to get the heat pump above the anticipated snow level and the heat pump is 8 inches off of the ground, that is enough to protect the unit from over 8 feet of snow accumulation if there is nowhere for the snow melt to drain below the unit base.
When installers understand why there is a need to get the heat pump up off of the pad for proper drainage, they will be less apt to disregard that portion of the instructions.
PUMP IT UPContractors can send plastic pump ups to the jobsite with the pad, but that in no way ensures the installers will take the time to use them. And if only one installer is setting the heat pump, manipulating the unit onto pump ups can be a real pain.
As for bricks and wood, I’ve seen many instances where these items are used “under” the pad, with the heat pump setting directly on the pad. The installers insist that they have followed the manufacturer’s instructions by getting the heat pump above anticipated snow fall, but there is still not proper drainage to keep ice from forming around the base of the coil.
One major solution for the improper heat pump installs is the use of new heat pump pads. The one-piece design allows for installation of the heat pump by one person, as easily as placing the heat pump on a flat pad. I have set large heat pumps on these pads by myself with no problems - and I have become older and out of shape over the years.
Another complaint about pump ups and pads is the support of the compressor section, and sound reverberation from the compressor section not being properly supported; one of these new heat pump pads is shaped like a six-rayed starburst that gives support to the entire base of the heat pump. This particular pad also has a base that is pitched toward the perimeter, allowing condensate and rain water to drain away from the unit and rubber isolators.
My guess is that a great portion of warranty issues with heat pumps at this time of year can be reduced with a simple installation change to current, common practices. I am so tired of being the guy who has to tell contractors that the destruction of a heat pump could have been avoided so easily, that I will stay on my “get the pump up” pulpit until every heat pump is up and out of harm’s way.
Publication date: 05/23/2011