Guide to Installing Condensing Units

By Robert Thornton

When it comes to installing a condensing unit, some initial planning and prep work can help streamline the process. By surveying the general equipment layout and the specific refrigeration system, labor time can be greatly reduced and a proper installation is guaranteed.

There are numerous components to consider in a condensing unit installation in comparison to an evaporator installation. These components offer many advantages, depending on the application, and can protect the compressor, offer capacity control in varying loads, direct hot gas to a heat reclaim, provide defrost for air, electric, or hot gas evaporators, ensure proper oil in a compressor crankcase, offer quick checks of refrigerant levels, and many other functions. Fortunately, the actual mounting of a condensing unit is much easier than an evaporator, since there is no hanging on a ceiling or wall. Keeping these factors in mind, here are 10 tips for a successful condensing unit installation:

1. Before placing the unit, make sure the model, voltage, phase and refrigerant type are correct. The capacity of the condensing unit should match the application of the evaporator, and the refrigerant should be the same as the evaporator and its components. Reference the installation manual for helpful suggestions during the installation and start up process, such as mounting, piping, wiring, charging, and more.

2. Select a location in which the unit can be serviced easily and is strong enough to support the weight. Make sure that the placement doesn’t allow discharge air from another unit to be drawn into the intake of the condenser. After the unit is set in place, discard all shipping materials. Shipping materials should never be used for mounting. Instead, use steel framing or treated lumber and make sure to level the unit. Always anchor the unit to prevent shifting during operation, as shifting could cause piping to break.

3. Inspect and tighten all electrical connections, nuts, bolts, and fasteners that hold major components such as fan motors and blades, compressors, receivers, accumulators, oil separators, filters, and any piping clamps in place, as they may have come loose in shipment. An overall check for the integrity of the unit after shipping is a must. The compressor mounting feet may need to be loosened to move freely on the springs. Not all compressors have this option.

4. Piping the unit properly to ensure good oil return and low pressure drop with no restriction is of the utmost importance. Use a line sizing chart to take the length of line run and capacity into consideration. The stub out connections are not always the correct size for every application. Additionally, make sure to use fully dehydrated copper tubing – Type “L” or type “K” is preferred. Proper piping practices are to be followed with an inert gas line always flowing during brazing to prevent scale and oxidation. Make sure that “P” traps are placed at the bottom of all suction risers and all lines are sloped in the direction of flow (1/4-in. per 10-ft. is suggested). If soft copper is used, never leave excess copper in a coil, which can cause an oil trap. Never let copper “sag,” as this can also cause an oil trap. While piping the unit, try to keep the compressor, components, and driers isolated. Make sure to properly support the pipe. The smaller the pipe size the more support is needed. The main purpose for support is to prevent vibration and sag that could lead to breakage. After the system is started, it may be necessary to install more supports if vibration is experienced.

5. Always leak check the unit before insulating so that all joints and connections can be easily seen. Open all service valves and pressurize the system to 150 psi with dry nitrogen and a small amount of refrigerant. Make sure to let the unit sit for a period of time to see if any leaks appear. An electronic leak detector and soap bubbles can be used to confirm if a leak has allowed the pressure to drop.

6. Insulate all piping. Suction lines need insulation to prevent excessive superheat, condensation drip, and excessive ice build up. The liquid line, when exposed to varying temperatures, can alter liquid temperature, which affects the way the expansion valve and nozzle perform and can also prevent flash gas at the thermal expansion valve.

7. Save time by starting an evacuation before wiring the system. To do this, relieve the dry nitrogen mix from the system. The small amount of refrigerant that was used for leak checking is allowed to be released. Hook the charging hoses to the high and low side and start the vacuum pump. A 500 micron evacuation is preferred. If manual lift stem solenoids are used, this is a good time to open them. If standard solenoids are used, further evacuation may be needed when the unit is powered to allow solenoids to open. If the vacuum is broken during evacuation to purge with refrigerant, this purging refrigerant must be reclaimed.

8. The serial tag, wiring diagram and installation manual that comes with the unit has all of the information for wiring and circuit protection. Local codes may vary, so be familiar with your local code. Some codes include: MCA (Minimum Circuit Ampacity) (used to size wire and current carrying components) and MOPD (Maximum Overcurrent Protection Device) the circuit breaker or fuse size.

There are many types of systems that require different diagrams. In order to know which diagram to use, get familiar with the equipment, its application and defrost type. Make sure to always use copper conductors and ground the unit.

9. Charge with the refrigerant designated for your system. Make sure that all components match the refrigerant type. Always mark the system with the type of refrigerant that’s used. If your system uses a head pressure control valve, the system should be charged with 90% of the receiver holding capacity plus any additional refrigerant required by a liquid line longer than 25 ft. Start charging liquid into the high side of the unit to break the vacuum. If the complete charge can’t be administered this way, finish charging through the low side. Lastly, always place a liquid drier in the charging line.

10. Hook up refrigerant gauges and ampereage meter before applying power. Make sure the oil level is at least 1/4 full. Adjust the room thermostat to the desired setting so that the solenoid energizes when power is applied. The low pressure switch should be set for approximately 5 psi cut out and 15 psi cut in for a typical pump down system. Set the high pressure switch according to refrigerant, typically 425 psi. Verify these settings with the unit running. Apply power. Check that the condenser fans are rotating in the right direction and that the amperage is correct. Make sure the compressor RLA is not exceeded. Observe suction and high side pressure as well as those temperatures. Be prepared to adjust compressor superheat to approximately 20F. Perform an operational check for defrost, pump down, and, if applicable, check the oil failure switch for proper operation.

Many manufacturers can build condensing units with most options installed. This saves both time and money on the jobsite and can possibly make a system operational much quicker. You also get the advantage of a factory installation without the hassle of purchasing components. Make sure to advise your dealer if you would the condensing unit to come with any factory options.

If an operational check doesn’t seem right, or if you have questions, you can always contact the manufacturer for advice. For additional information, always review the installations and operations manual.

Robert Thornton is a sales engineering specialist for Heatcraft Refrigeration Products.

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