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AAON CF Series Heat Pump Maintenance

The AAON CF Series Heat Pump Maintenance is a standard procedure that checks the operation quality of the machines components. Be sure to follow the safety steps provided to avoid any accidents.

MaintainX

04/26/2021

AAON CF Series Heat Pump Maintenance

The AAON CF Series Heat Pump Maintenance is a standard procedure that checks the operation quality of the machines components. Be sure to follow the safety steps provided to avoid any accidents.

Compressors

The scroll compressors are fully hermetic and require no maintenance except keeping the shell clean.

Refrigerant Filter Driers

Each refrigerant circuit contains a filter drier. Replacement is recommended when there is excessive pressure drop across the assembly or moisture is indicated in a liquid line sight glass.

Table 6 - Max Filter Drier Pressure Drops

Adjusting Refrigerant Charge

All AAON CF Series condensers and condensing units are shipped with a factory holding charge. The factory charge is different depending on the unit size and system (heat pump, modulating hot gas reheat, LAC). The factory charge per circuit is shown on the

Adjusting the charge of a system in the field must be based on determination of liquid sub-cooling and evaporator superheat. On a system with a thermostatic expansion valve liquid sub-cooling is more representative of the charge than evaporator superheat

CAUTION! COMPRESSOR LUBRICANT Polyolester (POE) and Polyvinylether (PVE) oils are two types of lubricants used in hydrofluorocarbon (HFC) refrigeration systems. Refer to the compressor label for the proper compressor lubricant type.

CAUTION! CLEAN AIR ACT The Clean Air Act of 1990 bans the intentional venting of refrigerant (CFC’s and HCFC’s) as of July 1, 1992. Approved methods of recovery, recycling or reclaiming must be followed. Fines and/or incarceration may be levied for non-co

Before Charging

Refer to the Unit Nameplate to determine which refrigerant must be used to charge the system.

Unit being charged must be at or near full load conditions before adjusting the charge.

Units equipped with hot gas bypass must have the hot gas bypass valve closed to get the proper charge.

Units equipped with hot gas reheat must be charged with the hot gas valve closed while the unit is in cooling mode. After charging, unit should be operated in reheat (dehumidification) mode to check for correct operation.

Units equipped with heat pump options should be charged in cooling mode to get the proper charge.

heating mode to check for correct charge. Charge may need to be adjusted for heating mode. If adjustments are made in the heating mode, cooling mode must be rerun to verify proper operation.

After adding or removing charge the system must be allowed to stabilize, typically 10-15 minutes, before making any other adjustments.

The type of unit and options determine the ranges for liquid sub-cooling and evaporator superheat. Refer to Table 7 when determining the proper sub-cooling.

For units equipped with low ambient (0°F) option see the special charging instructions at the end of this section.

Checking Liquid Sub-cooling

Measure the temperature of the liquid line as it leaves the condenser coil.

Read the gauge pressure at the liquid line close to the point where the temperature was taken. You must use liquid line pressure as it will vary from discharge pressure due to condenser coil pressure drop.

Convert the pressure obtained to a saturated temperature using the appropriate refrigerant temperature-pressure chart.

Subtract the measured liquid line temperature from the saturated temperature to determine the liquid sub-cooling.

Compare calculated sub-cooling to Table 7 for the appropriate unit type and options.

Table 7 - Acceptable Refrigeration Circuit Values

Notes

Must be charged with the hot gas valve closed. After charging, unit should be operated in reheat (dehumidification) mode to check for correct operation.

The sub-cooling value in this table is for the unit running in cooling mode of operation. After charging, unit should be operated in heating mode to check for correct operation

The sub-cooling value in this table is for the unit running in cooling mode of operation and the hot gas valve closed. After charging, unit should be operated in reheat (dehumidification) mode to check for correct operation and then in heating mode to che

Sub-cooling must be increased by 1°F per 10 feet of vertical liquid line rise for R-410A (AHU above CU). For example, a cooling only unit with hot gas reheat and a vertical liquid drop can charge to a sub-cooling value of 5-15°F, but a cooling only unit w

Checking Evaporator Superheat

Measure the temperature of the suction line close to the compressor.

Read gauge pressure at the suction line close to the compressor.

Convert the pressure obtained to a saturated temperature using the appropriate refrigerant temperature-pressure chart.

Subtract the saturated temperature from the measured suction line temperature to determine the evaporator superheat.

For refrigeration systems with tandem compressors, it is critical that the suction superheat setpoint on the TXV is set with one compressor running. The suction superheat should be 10-13°F with one compressor running. The suction superheat will increase w

liquid refrigerant to return to the compressors which will wash the oil out of the compressor. Lack of oil lubrication will destroy a compressor. Liquid sub-cooling should be measured with both compressors in a refrigeration system running.

Compare calculated superheat to the acceptable cooling mode superheat values of 8-15°F for all system types. Superheat will increase with long suction line runs.

CAUTION! EXPANSION VALVE ADJUSTMENT Thermal expansion valves must be adjusted to approximately 8-15°F of suction superheat. Failure to have sufficient superheat will damage the compressor and void the warranty.

Adjusting Sub-cooling and Superheat Temperatures

The system is overcharged if the sub-cooling temperature is too high compared to Table 7 and the evaporator is fully loaded (low loads on the evaporator result in increased subcooling) and the evaporator superheat is within the temperature range of 8-15°F

Correct an overcharged system by reducing the amount of refrigerant in the system to lower the sub-cooling.

CAUTION! DO NOT OVERCHARGE! Refrigerant overcharging leads to excess refrigerant in the condenser coils resulting in elevated compressor discharge pressure.

The system is undercharged if the superheat is too high and the sub-cooling is too low.

Correct an undercharged system by adding refrigerant to the system to reduce super heat and raise sub-cooling.

If the sub-cooling is correct and the superheat is too high, the TXV may need adjustment to correct the superheat.

Special Low Ambient Option Charging Instructions

For units equipped with low ambient control (LAC) refrigerant flood back option being charged when the ambient temperature is warm:

Once enough charge has been added to get the evaporator superheat and sub-cooling values to the correct setting, more charge must be added.

Add approximately 80% of the receiver tank volume to the charge to help fill the receiver tank. The additional charge is required for the system when running in cold ambient conditions.

For units equipped with low ambient refrigerant flood back option being charged when the ambient temperature is cold:

Once enough charge has been added to get the evaporator superheat and sub-cooling values to the correct setting, more charge may need to be added.

If the ambient temperature is 0°F no more charge is required. If the ambient temperature is around 40°F add approximately 40% of the receiver tank volume.

The unit will have to be checked for proper operation once the ambient temperature is above 80°F.

Oil Level

It is critical that the refrigerant line piping is designed to maintain proper oil return to the compressors. Some systems may require oil to be added in addition to what is provided in the compressors.

The oil is a PVE type and is available from your AAON Representative under part number V41850.

Proper oil level should be observed under minimum load conditions. On units equipped with tandem compressors, all oil is returned to the lead compressor in each tandem pair.

When only the lead compressor is running, the oil level should be a minimum of ⅜ from the bottom of the sight glass. With both compressors running, the level in the lead compressor should drop to the bottom of the sight glass and the level in the second c

Table 8 - R-410A Refrigerant Temperature-Pressure Chart

Lubrication

All original motors and bearings are furnished with an original factory charge of lubrication. Certain applications require bearings be re-lubricated periodically. The schedule will vary depending on operating duty, temperature variations, or severe atmos

Bearings should be re-lubricated at normal operating temperatures, but not when running.

Condenser Tube Inspection

The coils are leak tested at 650 psig, before shipment. AAON will not be responsible for loss of refrigerant. It is the responsibility of the installer to verify that the system is sealed before charging with refrigerant.

Maintenance Recommendations

Fan Motor Maintenance

Cleaning -: Remove

oil

dust

water

chemicals from exterior of motor

Keep motor air inlet and outlet open

Blow out interior of open motors with clean compressed air at low pressure.

Labeled Motors - It is imperative for repair of a motor with Underwriters’ Laboratories label that original clearances be held

plugs

screws

other hardware be fastened securely

parts replacements be exact duplicates or approved equals.

Violation of any of the above invalidates Underwriters’ Label.

Access Doors

If scale deposits or water is found around the access doors, adjust door for tightness. Adjust as necessary until leaking stops when door is closed.

Propeller Fans and Motors

The fans are directly mounted on the motor shafts and the assemblies require minimal maintenance except to assure they are clear of dirt or debris that would impede the airflow

Recommended Annual Inspection

In addition to the above maintenance activities, a general inspection of the unit surface should be completed at least once a year.

Air-Cooled Condenser

The air-cooled condenser section rejects heat by passing outdoor air over the fin tube coils for cooling of the hot refrigerant gas from the compressors.

The condenser coils should be inspected annually to ensure unrestricted airflow. If the installation has a large amount of airborne dust or other material, the condenser coils should be cleaned with a water spray in a direction opposite to airflow. Care m

E-Coated Coil Cleaning

Documented routine cleaning of e-coated coils is required to maintain coating warranty coverage.

WARNING! ELECTRIC SHOCK Electric shock hazard. Shut off all electrical power to the unit to avoid shock hazard or injury from rotating parts.

Surface loaded fibers or dirt should be removed prior to water rinse to prevent restriction of airflow. If unable to back wash the side of the coil opposite of the coils entering air side, then surface loaded fibers or dirt should be removed with a vacuum

If a vacuum cleaner is not available, a soft non-metallic bristle brush may be used. In either case, the tool should be applied in the direction of the fins. Coil surfaces can be easily damaged (fin edges bent over) if the tool is applied across the fins.

CAUTION! PRESSURE CLEANING High velocity water from a pressure washer or compressed air should only be used at a very low pressure to prevent fin and/or coil damages. The force of the water or air jet may bend the fin edges and increase airside pressure d

Use of a water stream, such as a garden hose, against a surface loaded coil will drive the fibers and dirt into the coil. This will make cleaning efforts more difficult. Surface loaded fibers must be completely removed prior to using low velocity clean wa

A monthly clean water rinse is recommended for coils that are applied in coastal or industrial environments to help to remove chlorides, dirt, and debris. It is very important when rinsing, that water temperature is less than 130° F and pressure is less t

An elevated water temperature (not to exceed 130° F) will reduce surface tension, increasing the ability to remove chlorides and dirt.

Quarterly cleaning is essential to extend the life of an e-coated coil and is required to maintain coating warranty coverage.

Coil cleaning shall be part of the unit’s regularly scheduled maintenance procedures. Failure to clean an e-coated coil will void the warranty and may result in reduced efficiency and durability.

CAUTION! COIL CLEANERS Harsh chemicals, household bleach, or acid cleaners should not be used to clean outdoor or indoor e-coated coils. These cleaners can be very difficult to rinse out of the coil and can accelerate corrosion and attack the e-coating. I

For routine quarterly cleaning, first clean the coil with the approved coil cleaner as mentioned in the next section. After cleaning the coils with the approved cleaning agent, use the approved chloride remover to remove soluble salts and revitalize the u

Recommended Coil Cleaner

The following cleaning agent, assuming it is used in accordance with the manufacturer’s directions on the container for proper mixing (4:1 condensers & 8:1 evaporators) and cleaning, has been approved for use on ecoated coils to remove

mold

mildew

dust

soot

greasy residue

lint and other particulate:

Enviro-Coil Concentrate, Part Number HEC01.

Recommended Chloride Remover

CHLOR*RID DTS™ should be used to remove soluble salts from the e-coated coil, but the directions must be followed closely. This product is not intended for use as a degreaser. Any grease or oil film should first be removed with the approved cleaning agent

Remove Barrier - Soluble salts adhere to the substrate. For the effective use of this product, the product must be in contact with the salts. These salts may be beneath any soils, grease or dirt; therefore, these barriers must be removed prior to applicat

Apply CHLOR*RID DTS - Apply directly onto the substrate. Sufficient product must be applied uniformly across the substrate to thoroughly wet out surface, with no areas missed. This may be accomplished by use of a pump-up sprayer or conventional spray gun.

Rinse - It is highly recommended that a hose be used. A pressure washer on a high pressure setting will damage the fins. The water to be used for the rinse is recommended to be of potable quality, though a lesser quality of water may be used if a small am

Service

If the unit will not operate correctly and a service company is required, only a company with service technicians qualified and experienced in both refrigerant chillers and air conditioning are permitted to service the systems to keep warranties in effect

Warranties

Please refer to the limitation of warranties in effect at the time of purchase.

Replacement Parts

Parts for AAON equipment may be obtained by contacting your local AAON representative. When ordering parts, reference the serial number and part number located on the external or internal nameplate of the unit.

NOTE: Before calling, technician should have model and serial number of the unit available for the customer service department to help answer questions regarding the unit.

Source: Aaon

Please note that any procedure, checklist, or other document available in the MaintainX Procedure Hub is provided for general education and information only and does not constitute legal, medical, or financial advice. MaintainX makes the materials available AS IS and AS PROVIDED, without warranties of any kind. By downloading or using any such materials, you assume the risk that they may not be appropriate for your specific situation and agree that you are solely responsible for any such use, including compliance with applicable law and with meeting any conditions of product warranties.

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