Maintenance, Service, and Repair of Refrigeration Equipment
Learning Objectives: When you complete this assignment you will understand different types of maintenance equipment and methods for basic maintenance, service, and repair of refrigeration systems and components
As a refrigeration technician, you must be able to maintain, service, and repair refrigeration equipment. This phase of our course provides information on different jobs that you may be assigned. It is not intended to be all encompassing. Manufacturers also provide instruction manuals to aid you in maintaining and servicing their equipment
Repair and service work on a refrigeration system consists mainly of containing refrigerant and measuring pressures accurately. One piece of equipment is the refrigerant gauge manifold set (fig. 6-48). It consists of a 0-500 psig gauge for measuring pressure at the compressor high side, a compound gauge (0-250 psig and 0 to -30 inches of mercury) to measure the low or suction side, and valves to control admission of the refrigerant to the refrigeration system. It also has the connections and lines required to connect the test set to the system. Depending on test and service requirements, the gauge set can be connected to the low side, the high side, a source of vacuum, or a refrigerant cylinder. A swiveling hanger allows the test set to be hung easily, and the three additional blank connections allow for securing the open ends of the three lines when the gauge set is not in use. There is always a path from the low-side and high-side input to the low-side and high-side gauge (fig. 6-49)
Figure 6-48.—Refrigerant gauge manifold set
Figure 6-49.—Internal view of a refrigerant gauge manifold set
Another important piece of equipment is the portable vacuum pump--s a sealed unit consisting of a single-piston vacuum pump driven by an electric motor. A vacuum pump is the same as a compressor, except the valves are arranged so the suction valve is opened only when the suction developed by the downward stroke of the piston is greater than the vacuum already in the line. This vacuum pump can develop a vacuum close to -30 inches of mercury, which can be read on the gauge mounted on the unit (fig. 6-50). The pump is used to reduce the pressure in a refrigeration system to below atmospheric pressure
Figure 6-50.—Portable vacuum pump
Various manufacturers manufacture hermetic refrigeration systems used by the Navy; therefore, the connectors and size of tubing vary. The Table of Allowance provides for a refrigeration service kit that contains several adapters, wrenches, and other materials to help connect different makes of systems to the refrigerant manifold gauge set and the vacuum pump lines. A table affixed to the lid of the storage container identifies the adapter you should use for a particular refrigeration unit
Refrigerants are shipped in compressed gas cylinders as a liquid under pressure. Liquids are usually removed from the shipping containers and transferred to a service cylinder (fig. 6-51)
Figure 6-51.—Method of transferring refrigerants to service cylinders
Before attempting transfer of refrigerants from a container to a cylinder, precool the receiving cylinder until its pressure is lower than that of the storage container or cylinder. Precool by placing the cylinder in ice water or a refrigerated tank. You must also weigh the service cylinder, including cap, and compare it with the tare weight stamped or tagged on the cylinder. The amount of refrigerant that may be placed in a cylinder is 85 percent of the tare weight (the weight of a full cylinder and its cap minus the weight of the empty cylinder and its cap)
To transfer refrigerants, connect a flexible charging line on a 1/4-inch copper tube several feet long with a circular loop about 8 to 10 inches in diameter. Be sure to install a 1/4-inch refrigerant shutoff valve (fig. 6-51) in the charging line to the service cylinder. This valve should be inserted so no more than 3 inches of tubing is between the last fitting and the valve itself. This arrangement prevents the loss of refrigerant when the service drum is finally disconnected. The entire line must be cleared of air by leaving the flare nut on the service cylinder loose and cracking the storage cylinder valve. This arrangement allows refrigerant to flow through the tubing, clearing it. After clearing, tighten the flare nut and then open the valve on the service cylinder, the valve on the storage cylinder, and then the 1/4-inch valve in the refrigerant line. When the weight of the service cylinder shows a sufficient amount of refrigerant is in the serviced cylinder, close all valves tightly, and disconnect the charging line at the service cylinder
To warm refrigerant containers or cylinders for more rapid discharge, use care to prevent a temperature above 120°F because the fusible plugs in the cylinder and valve have a melting point of about 157°F
Evacuating and Charging a System
One of your jobs will be charging a system with refrigerant. If a system develops a leak, you must repair it first, then charge the system. Similarly, if a component of the system becomes faulty and must be replaced, some refrigerant will be lost and the system will require charging
Figure 6-52.—Connections for drawing a vacuum
Before a system can be charged, all moisture and air must be eliminated from the components by drawing a vacuum on the system. To draw a vacuum on the system, proceed as follows:
- Connect the portable vacuum pump to the vacuum fitting on the refrigerant manifold gauge set (fig. 6-48)
- Connect the LO line (suction) to the suction service valve of the compressor, using appropriate connectors if required
- Turn the suction service valve to mid-position, so vacuum draws from the compressor crankcase and suction line back through the evaporator, expansion valve, and liquid line When the receiver service valve, condenser service valve, and discharge service valve are open, the pump draws back through the receiver and condenser to the compressor
- Attach one end of a 1/4-inch copper tube to the vacuum pump discharge outlet (fig. 6-52) Allow the vacuum pump to draw a vacuum of at least 25 inches. Submerge the other end of the copper tubing under 2 or 3 inches of clean compressor oil contained in a bottle
- Continue to operate the vacuum pump until there are no more bubbles of air and vapor in the oil, which indicates that a deep vacuum has been obtained
- Maintain the deep vacuum operation for at least 5 minutes, and then stop the vacuum pump Leaking discharge valves of a vacuum pump cause oil to be sucked up into the copper discharge tube. Keep the vacuum pump off at least 15 minutes to allow air to enter the system through any leaks. Then start the vacuum pump. A leaky system causes bubbling of the oil in the bottle
- Examine and tighten any suspected joints in the line, including the line to the vacuum pump. Repeat the test
In most small refrigerating systems, low-side charging (fig. 6-53) is generally recommended for adding refrigerant after repairs have been made.
Figure 6-53.—Connections for low-side charging
After the system has been cleaned and tested for leaks, the steps to charge the system are as follows:
- Connect a line from a refrigerant cylinder to the bottom center connection on the refrigerant gauge manifold set. Be certain the refrigerant cylinder is in a vertical position, so only refrigerant in the form of gas, not liquid, can enter the system. Leave the connection loose and crack the valve on the cylinder. This fills the line with gas and clears the air from the line. After clearing, tighten the connection
- Connect a line from the LOW (LO) valve (suction) on the gauge manifold set to the suction service valve of the compressor
- Start the compressor
- Open the valve on the cylinder and the LOW (LO) valve (suction) on the gauge manifold set
- Open the suction service valve on the compressor to permit the gas to enter the compressor where it will be compressed and fed to the high side. Add the refrigerant slowly and check the liquid level indicator regularly until the system is fully charged. It is easy to check the receiver refrigerant level in some makes of condensing units because the receiver has minimum and maximum liquid level indicator valves which show the height of the liquid level when opened. If a liquid line sight glass is used, the proper charge may be determined when there is no bubbling of refrigerant as it passes by the glass. The sight glass will appear empty
Again, be certain the refrigerant cylinder is in the vertical position at all times; otherwise, the liquid refrigerant will enter the compressor and, liquid not being compressible, damage the piston or other parts of the compressor
The best time to test joints and connections in a system is when there is enough pressure to increase the The best ti me to test joints and connections in a rate at which the refrigerant seeps from the leaking joint. There is usually enough pressure in the high-pressure side of the system; that is, in the condenser, receiver, and liquid line, including dehydrators, strainers, line valves, and solenoid valves. This is not necessarily true of the low-pressure side of the system, especially if it is a low-pressure installation, such as for frozen foods and ice cream, where pressures may run only slightly above zero on the gauge. When there is little pressure, increase the pressure in the low-pressure side of the system by bypassing the discharging pressure from the condenser to the low-pressure side through the service gauge manifold Small leaks cannot be found unless the pressure inside the system is at least 40 to 50 psi, regardless of the method used to test for leaks.
Halide Leak Detector
The use of a halide leak detector (fig. 6-54) is the most positive method of detecting leaks in a refrigerant system using halogen refrigerants (R-12, R-22, R-11, R-502, etc.). Such a detector consists essentially of a torch burner, a copper reactor plate, and a rubber exploring hose.
Figure 6-54.—Halide leak detector.
Detectors use acetylene gas, alcohol, or propane as a fuel. A pump supplies the pressure for a detector that uses alcohol. If a pump-pressure type of alcohol-burning detector is used, be sure that the air pumped into the fuel tank is pure.
An atmosphere suspected of containing a halogen vapor is drawn through the rubber exploring hose into the torch burner of the detector. Here the air passes over the copper reactor plate, which is heated to incandescence. If there is a minute trace of a halogen refrigerant present, the color of the torch flame changes from blue (neutral) to green as the halogen refrigerant contacts the reactor plate. The shade of green depends upon the amount of halogen refrigerant; a pale green color shows a small concentration and a darker green color, a heavier concentration. Too much of a halogen refrigerant causes the flame to burn with a vivid purple color. Extreme concentrations of a halogen refrigerant may extinguish the flame by crowding out the oxygen available from the air.
Normally, a halide leak detector is used for R-12 and R-22 systems. In testing for leaks always start at the highest point of the system and work towards the lowest point because halogen refrigerants are heavier than air.
When using a leak detector, you will obtain the best results by following the Precautions listed below:.
- Be sure the reactor plate is properly in place.
- Adjust the flame so it does not extend beyond the end of the burner. (A small flame is more sensitive than a large flame. If it is hard to light the torch when it is adjusted to produce a small flame, block the end of the exploring hose until the fuel ignites; then gradually open the hose.)
- Clean out the rubber exploring hose if the flame continues to have a white or yellow color. (A white or yellow flame is an indication that the exploring tube is partially blocked with dirt.)
- Check to see that air is being drawn into the exploring tube; this check can be made from time to time by holding the end of the hose to your ear.
- Hold the end of the exploring hose close to the joint being tested to prevent dilution of the sample by stray air currents.
- Move the end of the exploring hose slowly and completely around each joint being tested. (Leak testing cannot be safely hurried. There is a definite time lag between the moment when air enters the exploring hose and the moment it reaches the reactor plate; permit enough time for the sample to reach the reactor plate.)
If a greenish flame is noted, repeat the test in the same area until the source of the refrigerant is located.
Always follow a definite procedure in testing for refrigerant leaks, so none of the joints are missed. Even the smallest leaks are important. However slight a leak may seem, it eventually empties the system of its charge and causes faulty operation. In the long run, the extra time spent in testing each joint will be justified. A refrigerant system should never be recharged until all leaks are discovered and repaired.
Electronic Leak Detector
The most sensitive leak detector of all is the electronic type. The principle of operation is based on the dielectric difference of gases. In operation, the gun is turned on and adjusted in a normal atmosphere. The leak-detecting probe is then passed around the surfaces suspected of leaking. If there is a leak, no matter how tiny, the halogenated refrigerant is drawn into the probe. The leak gun then gives out a piercing sound, or a light flashes, or both, because the new gas changes the resistance in the circuit.
When using an electronic leak detector, minimize drafts by shutting off fans or other devices that cause air movement. Always position the sniffer below the suspected leak. Because refrigerant is heavier than air, it drifts downward. Always remove the plastic tip and clean it before each use. Avoid clogging it with dirt and lint. Move the tip slowly around the suspected leak.
Soap and Water Test
Soap and water may be used to test for leakage of refrigerant with a pressure higher than atmospheric pressure. Make a soap and water solution by mixing a lot of soap with water to a thick consistency. Let it stand until the bubbles have disappeared, and then apply it to the suspected leaking joint with a soft brush. Wait for bubbles to appear under the clear, thick soap solution.
Find extremely small leaks by carefully examining suspected places with a strong light. If necessary, use a mirror to view the rear side of joints or other connections suspected of leaking.
Quality refrigeration repair includes preventing loss of refrigerant in the system. Whenever a component is removed from the system, the normally closed system is opened and, unless precautions are taken, refrigerant is lost to the atmosphere. The best way to contain the refrigerant (gas and liquid) is to trap it in the condenser and receiver by pumping down the system.
To pump down the system, proceed as follows:
- Secure electric power to the unit and connect the refrigerant manifold test set, as shown in figure 6-55.
- Close the receiver stop (king) valve (by turning the valve stem inwards as far as it will go), and close both gauges on the gauge manifold (LO and HI valves).
- Start the compressor and mid-seat the discharge and suction service valves.
- Operate the compressor until the pressure on the suction (LO) gauge on the manifold shows a vacuum at 0 to 1 psi.
- Stop the compressor. If the pressure rebuilds appreciably, operate the unit again until pressure registers between 0 to 1 psi. Repeat this step until the pressure no longer rebuilds appreciably.
- When suction pressure remains at about 0 to 1 pound as read on the compound gauge, then front-seat the suction and discharge service valves (fig. 6-56). This procedure traps practically all the refrigerant in the condenser and receiver.
Figure 6-55.—Connections for pumping down a system.
Figure 6-56.—Three-way service valve positions.
Recovery, Recycling, and Reclaiming Refrigerant
Laws governing the release of chlorofluorocarbon refrigerants (CFCs) into the atmosphere have resulted in the development of procedures to recover, recycle, and reuse these refrigerants. Many companies have developed equipment necessary to prevent the release of CFCs into the atmosphere. Refrigerant recovery management equipment can be divided into three categories—recovery, recycle, and reclaiming equipment.
Removing refrigerant from a system in any condition and storing it in an external container is called "recovery." Removal of refrigerant from the system is necessary, in some instances, when repair of a system is needed. To accomplish this, you can use special recovery equipment, which is now a requirement when removing refrigerant from a system. This equipment ensures complete removal of the refrigerant in the system.
Recovery is similar to evacuating a system with the vacuum pump and is accomplished by either the vapor recovery or liquid recovery method. In the vapor recovery method (fig. 6-57), a hose is connected to the low-side access point (compressor suction valve) through a filter-drier to the transfer unit, compressor suction valve. A hose is then connected from the transfer unit, compressor discharge valve to an external storage cylinder. When the transfer unit is turned on, it withdraws vapor refrigerant from the system into the transfer unit compressor, which, in turn, condenses the refrigerant vapor to a liquid and discharges it into the external storage cylinder.
Figure 6-57.—The vapor recovery method.
In the liquid recovery method (fig. 6-58), a hose is connected to the low-side access point to the transfer unit compressor discharge valve. A hose is then connected from the transfer unit compressor suction valve through a filter-drier to a two-valve external storage cylinder. A third hose is connected from the high-side access point (liquid valve at the receiver) to the two-valve external storage cylinder. When the transfer unit is turned on, the transfer unit compressor pumps refrigerant vapor from the external storage cylinder into the refrigeration system, which pressurizes it. The difference in pressure between the system and the external storage cylinder forces the liquid refrigerant from the system into the external cylinder. Once the liquid refrigerant is removed from the system, the remaining vapor refrigerant is removed using the vapor recovery method as previously described.
Figure 6-58.—The liquid recovery method.
Most recovery units automatically shut off when the refrigerant has been completely recovered, but check the manufacturer's operational manual for specific instructions. You should make sure that the external storage cylinder is not overfilled. Eighty percent capacity is normal. If the recovery unit is equipped with a sight-glass indicator, any changes that may occur should be noted.
The process of cleaning refrigerant for reuse by oil separation and single or multiple passes through filter-driers which reduce moisture, acidity, and matter is called "recycling." In the past, refrigerant was typically vented into the atmosphere. Modern technology has developed equipment to enable reuse of old, damaged, or previously used refrigerant. Refrigerant removed from a system cannot be simply reused—it must be clean. Recycling in the field as performed by most recycling machines reduces the contaminants through oil separation and filtration. Normally recycling is accomplished during the recovery of the vapor or liquid refrigerant by use of equipment that does both recovery and recycling of refrigerant.
Recycling machines use either the single-pass or multiple-pass method of recycling. The single-pass method (fig. 6-59) processes refrigerant through as filter-drier and/or uses distillation. It makes only one pass through the recycling process to a storage cylinder. The multiple-pass method (fig. 6-60) recirculates refrigerant through the filter-drier many times, and after a period of time or number of cycles, the refrigerant is transferred to a storage cylinder.
Figure 6-59.—Single-pass method of recycling.
Figure 6-60.—Multiple-pass method of recycling.
The reprocessing of a refrigerant to original production specifications as verified by chemical analysis is called "reclaiming." Equipment used for this process must meet SAE standards and remove 100 percent of the moisture and oil particles.
Most reclaiming equipment uses the same process cycle for reclaiming refrigerant. The refrigerant enters the unit as a vapor or liquid and is boiled violently at a high temperature at extreme high pressure (distillation). The refrigerant then enters a large, unique separator chamber where the velocity is radically reduced, which allows the high-temperature vapor to rise. During this phase all the contaminants, such as copper chips, carbon, oil, and acid, drop to the bottom of the separator to be removed during the "oil out" operation. The distilled vapor then leaves the separator and enters an air-cooled condenser where it is converted to a liquid. Then the liquid refrigerant passes through a filter-drier into a storage chamber where the refrigerant is cooled to a temperature of 38°F to 40°F by an evaporator assembly.
Component Removal or Replacement
To maintain a refrigerant system at a optimum operating condition sometimes requires removal or replacement of some component. Procedures for removal and replacement of some of the components most often requiring action are covered in this section.
Removing Expansion or Float Valves
To help ensure good results in removing expansion or float valves, you should pump the system down to a suction pressure of just over zero. You should do this at least three times before removing the expansion valve. Plug the opened end of the liquid line and evaporator coil to prevent air from entering the system. Repair or replace the expansion valve and connect it to the liquid valve. Crack the receiver service valve to clear air from the liquid line and the expansion valve. Connect the expansion valve to the evaporator coil inlet and tighten the connection. Pump a vacuum into the low side of the system to remove any air.
Replacing an Evaporator
To replace an evaporator, pump down the system and disconnect the liquid and suction lines. Then remove the expansion valve and the evaporator. Make the necessary repairs or install a new evaporator as required. Replace the expansion valve and connect the liquid and suction lines. Remove moisture and air by evacuating the system. When the evaporator is back in place, pump a deep vacuum as in starting a new installation for the first time. Check for leaks and correct them if they occur. If leaks do occur, be certain to repair them; then pump the system into a deep vacuum. Repeat the process until no more leaks are found.
Removing the Compressor
Using the gauge manifold and a vacuum pump, pump down the system. Most of the refrigerant will be trapped in the condenser and the receiver. To remove the compressor from service, proceed as follows:
- Once the pump down is complete, the suction valve should already be closed and the suction gauge should read a vacuum. Mid-seat the discharge service valve. Open both manifold valves to allow high-pressure vapor to build up the compressor crankcase pressure to 0 psi. Front-seat (close) the discharge service valve.
- Then crack the suction service valve until the compound gauge reads 0 to 1 psi to equalize the pressures and then front-seat the valve.
- Joints should be cleaned with a grease solvent and dried before opening. Unbolt the suction service and discharge service valves from the compressor. DO NOT remove the suction or discharge lines from the compressor service valves.
- Immediately plug all openings through which refrigerant flows using dry rubber, "cork" stoppers, or tape.
- Disconnect the bolts that hold the compressor to the base and remove the drive belt or disconnect the drive coupling. You can now remove the compressor.
Removing Hermetic Compressors
Systems using hermetic compressors are not easily repaired, as most of the maintenance performed on them consists of removal and replacement.
- Disconnect the electrical circuit including the overload switch.
- Install a gauge manifold. Use a piercing valve (Schraider) if needed.
- Remove the refrigerant using an EPA approved recovery/recycling unit.
- Disconnect the suction and discharge lines. Using a pinching tool, pinch the tubing on both the suction and discharge lines, and cut both lines between the compressor and the pinched area.
- Disconnect the bolts holding the compressor to the base and remove the compressor.
Do not forget to pump down the system and equalize the suction and head pressure to the atmosphere, if applicable. Wear goggles to prevent refrigerant from getting in your eyes. After replacement, the procedures given for removing air and moisture and recharging the system can be followed; however, the procedures may have to be modified because of the lack of some valves and connections. Follow the specific procedures contained in the manufacturer's manual.