Wheeler On HVACR:
The Crucial Contractor Effect
It's surprising how many people outside our industry read my columns in SUPPLY HOUSE TIMES on the Internet. In fact, I've been getting questions from non-industry readers on a regular basis for many years now. Some of the most common questions they ask have to do with the new refrigerants, compressor types, problems they are experiencing with their equipment, and just which brand of equipment I would recommend.
When it comes to which brand I prefer, I do like certain features on certain brands. However, there are wide varieties of equipment types (e.g., air-conditioning, gas heating, electric heating, oil heating, heat pumps, refrigeration, etc.) and no brand is the best all across the line. However, as I often reply to end users, I think that the choice of installing contractors is far more important than equipment brand, because even the best-designed equipment will perform poorly and fail early if it is mis-installed. And believe it or not, that is all too often what happens. Let's consider some of the many mistakes that installing contractors often make. For brevity I will cover just air-conditioning mistakes here.
Any electrical voltage drops caused by poor connections or improper line sizing causes poor operating efficiency, short compressor and motor life, and erratic equipment operation. Yet, it's surprising how few contractors check the voltage at an operating condensing unit, for example, after a new installation.
Condensing Unit Location
For a condensing unit to function properly it should be located away from bedroom windows (noise) and have enough free room for ambient-temperature outdoor air flow - unimpeded by walls, bushes, overhangs, and recirculation from its own discharge air or the discharge air from nearby units. In addition, the wind direction should never blow against the discharge air (horizontal-discharge).
Refrigerant lines should always be sized per sizing charts (not by connecting-pipe sizes) with no kinks or restrictions. In addition, line lengths should be no shorter than 25 feet and no longer than 75 feet. Short line lengths promote refrigerant compressor slugging, while overly long line lengths result in compressor-oil dilution (because of too much added refrigerant), lost efficiency (due to pressure losses), and increased likelihood of compressor damage due to huge amounts of refrigerant migration after shutdown.
Dehydration And Charge
One of the worst and most common offenses contractors commit is putting (and not removing) moisture, air, and contaminants into systems. You see it all the time on new-construction sites: Refrigerant lines simply taped over. Anytime air is allowed to enter refrigerant lines, the air -- along with its moisture and grit -- must be totally removed, or the compressor life will be shortened drastically. This absolutely requires two steps that are rarely seen anymore:
1. Installation of a liquid-line filter/drier.
2. Deep evacuation with a good vacuum pump and electronic vacuum gage.
No, purging just doesn't work, and it's now illegal.
Yes, I like to see liquid-line filter/driers installed on every job. They simply increase compressor life. What about suction-line driers? Save them for compressor changeout situations, then remove them. The suction line is simply too affected by pressure drops to leave them in the system.
Also, whenever the refrigerant lines exceed 50 feet and/or when a liquid-line filter/dryer is installed, a small additional charge must be weighed in. The typical field-charging method of adding refrigerant into the suction line until it gets cold results in a gross overcharge which reduces efficiency and shortens compressor life.
This is something that I could write about for hours. However, on new installations the most common equipment-damaging problems are restricted airflow and bends/takeoffs that are located too close to the discharge or return plenums. Too little air results in poor sensible cooling, coil freezeups, poor operating efficiency, dripping connectors or discharge diffusers, and flooded compressors. Poorly located duct bends or takeoffs cause uneven air distribution across the evaporator coils, which results in lost capacity and efficiency, and in compressor flooding.
Here in the South where flex-duct has become king in new-home construction, restricted and misaligned airflow is usually caused by poor installations and poor duct designs (often no design at all).
Of course, once people have settled into their homes, the most common air-conditioning complaint is a warm room in the house. This becomes an irresolvable problem when contractors save money by not installing balance dampers, and when ducts are kinked or undersized for the length of run. As a result, a common (foolish) solution is to try to move the thermostat. That just creates other problems.
I guess I could go on talking about such things as poor condensate-line installations and the like, but you get the idea. Yes, there are some features of some brands that I really like, but no brand that I like all across the line. However, most brands will provide a satisfactory life expectancy and operate well if they are simply installed properly. So I tell people who write and ask about my favorite brands to first find a contractor who they know does the best job - and expect him to charge more, because a better job is crucial to satisfactory equipment operation. And if he's that good, trust his brand recommendation.