The employees at Heatcraft supplied The News with suggestions for a successful refrigeration system installation. In the first installment last week, points were provided regarding expansion valve selection and adjustment, evaporator replacement, piping practices, and defrost setting. In this final installment, topics covered include wiring, outdoor unit replacement, nozzle selection, and insulating lines.
WiringPrior to an installation, you need to evaluate your system and determine the type and gauge of wire required for that particular job. For each length of wire, consider all loads that will be powered on that circuit, including relays, contactors, microprocessors, and solenoids.
Add up all of these loads to determine the proper gauge wire. Measure how long your wire runs are and make sure you have sufficient amperage capability in your transformer and wire gauge to pull in the contactors. The longer the length, the higher the gauge you need to pull the same amperage.
The transformer should also be checked to ensure that its VA rating is sufficient.
For long runs of low-voltage power (such as a 24-vac, Class II control circuit), determining the correct wiring and transformers is critical for the correct operation of low-voltage components.
You may find that the wire powering a microprocessor also powers relays and contactors. The wire and transformer should be sized so that operation of the components does not affect the operation of the microprocessor.
Jim Kitchen, manager of the research and development laboratory, provides this scenario: “One sign of not having enough amperage at your microprocessor is the display resetting or flickering when a contactor or relay is energized. This often appears as an intermittent problem that you would see only at the moment the contactor is energized.”
In this case, check the transformer’s VA rating first, then make sure all terminal connections are tight. If all seems OK, you most likely need a thicker gauge wire.
In addition, refer back to the installation and maintenance guide for the manufacturer’s recommendations. Once you know what gauge wire you will need for that particular job, stock it on your truck.
Outdoor unit replacementWhen placing your condensing unit or remote condenser, allow for plenty of outside air to get into your unit. That includes space away from walls, fences, and other units. Also, make sure one unit’s exhaust is not feeding into another unit’s intake.
Each unit should be located so that air may circulate freely and not be recirculated. For proper airflow and access, all sides of the unit should be a minimum of the width of the unit “W” away from any wall or obstruction. It is preferred that this distance be increased whenever possible.
Also, make sure you are providing yourself enough clearance to come back and service the unit. Make sure all panels can open freely and that you have space to maneuver tools and equipment.
And don’t forget to look up — overhead obstructions need to be avoided for proper airflow and safety.
Nozzle selectionBefore you install the expansion valve on the distributor of the evaporator, the proper distributor nozzle must be installed.
Most evaporators come with two distributor nozzles, one for R-22 and another for most other refrigerants. The nozzles shipped with the evaporator are sized to meet most standard applications. One of these nozzles will be used in the majority of applications.
If the nozzle is oversized, the refrigerant tends to take the flow of gravity, going through the oversized opening, dropping to the bottom tubes. You’ll notice one portion fed more than another, in coil freezing or sweating.
“Without proper feeding, the evaporator cannot accept a full load condition,” said Robert Thornton, application engineer. “You’re basically just going to build frost unevenly until you have a frozen-up coil with a snowball effect of low suction pressure and floodback on the compressor.”
If your nozzle is too small, it acts like a restriction in the system. Thornton offered this explanation: “You starve your coil and end up running very low suction pressures, which can also overheat the compressor and can eventually cause compressor failure.”
Insulating linesA refrigeration system involves a delicate balance of fluid volumes at a particular temperature and pressure flowing through a carefully designed system.
To function optimally, fluid temperatures must not pick up or lose heat from the surrounding environment until they are supposed to.
Therefore, after the final leak test, refrigerant lines exposed to high ambient conditions should be insulated to reduce heat loss or gain and prevent the formation of flash gas in liquid lines. Proper insulation maintains consistent temperature, allowing the expansion valve and nozzle to work properly.
“It goes back a little bit to the expansion valve sizing,” said Mike Jarrell, manager of application engineering. “You base expansion valve size on a certain liquid temperature. Now if they take this liquid line, which is just a copper tube, and run it through a freezer — and it’s 10Â°F in that freezer — by the time that liquid travels 40 feet, it can go from 50Â° to as low as 10Â°. By then, standard components like expansion valves and nozzles are just way oversized and can’t work right.”
Suction lines should be insulated with 3/4-in. wall insulation, while liquid lines should be insulated with 1/2 in. or better.
The insulation located in outdoor environments should be protected from UV exposure to prevent deterioration of insulating value.
“Insulation on the suction line will ensure cooler refrigerant return gas to the compressor for more cooling,” said service engineer Galen Holzhausen. “This also keeps the motor in the compressor cool.”
The thickness is determined by the environment the pipe is going through. It may be a boiler room, a freezer, or it may go outside of the building. It must be thick enough to prevent condensation on the outside of the insulation. This is determined by the temperature of the suction line you are running and by the R factor of the insulation.
By following these guidelines, refrigeration contractors have a much better chance for a successful installation.