Refrigerator Troubleshooting Diagram

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Troubleshooting Portable Freezers

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Many uses can be found for portable freezers. For example, much of the ice cream sold during the summer months is sold from refrigerated trucks. It is essential that these trucks have reliable portable freezing units. See Figs. 13-22 and 13-23.

The compressor is run by 110/120-V, 60-Hz AC. It runs during the night when the truck is out of service. A small fan circulates the cold air. The fan runs on the truck battery during the day. At night, it is plugged into line current (120-V, AC).

This unit uses a hermetically sealed compressor designed for use with R-22. About 10 or 12 oz of R-22 are used for a full charge.

If the machine runs short of refrigerant, it should be allowed to warm to room temperature and checked for leaks with a halide torch. For finding small leaks, at least 90 lb of internal pressure are needed. It maybe necessary to add refrigerant to obtain this pressure. If so, connect the suction-line service opening to a drum of refrigerant (probably R-22), making sure the drum remains upright so that only gas will enter the unit.

Never connect in this manner a drum that is warmer than any part of the system. The gas will condense in the system, resulting in overcharge and waste of refrigerant.

If the unit is charged due to leaks, or any major repairs are made on the system, it is recommended that a new drier be installed. When replacing the original drier, be certain that the replacement drier has a good filter and strainer incorporated with the drying agent.

If a gas leak has allowed air to enter the system, the system must be evacuated or thoroughly cleaned with R-22. A new drier must be installed before charging. Air remaining in the system cannot be purged off. It permeates the complete system and is not trapped in the high side as in other systems using a liquid receiver.

Allow pressure to build to approximately 100 lb in the unit and shut off the charging valve immediately. After the unit is started, add refrigerant slowly until backpressure is between 10 and 16 lb, depending on the ambient temperature. (A high-ambient temperature will produce a higher head and back pressure.) The back pressure will then remain about the same until the eutectic (contents of the freezer) is completely frozen.

The charge should be checked again when the cabinet is around −15°F (−26°C) or colder. Then, with the condensing unit running, the suction line should frost out of the cabinet about 6 to 8 in. The desired frost line can be obtained by adding or purging of refrigerant (make sure the purged refrigerant is captured and reclaimed) a little at a time, allowing time for the system to equalize. Ifthe compressor will not start, but the condenser fan isrunning, check the head and back pressures. If the pressures are not equal, a capillary tube maybe clogged with moisture or foreign material. Heating the end of the capillary tube where it enters the cabinet will usually begin to equalize pressures if the restriction is due to moisture freezing. Evacuate the system, install a new drier, and recharge the system as described already. If the capillary tube is clogged with material other than frozen moisture, it should be replaced.

When the compressor does not start and the head and back pressures are approximately equal, check for trouble as follows.

Check the line voltage by holding the voltmeter leads on contacts of the motor base plug. Take a reading when the overload protector clicks in and the compressor is trying to start. This reading should be 100 V or more. If less, the trouble is probably in the supply line.

• Replace the capacitor, if the unit has one.
• Replace the relay and/or overload.

If, after these checks, the compressor will not start, the unit should be returned to the manufacturer.

Figure 13-24 shows an ice-cream vending unit. Most of the mechanical parts are located on top of the unit to prevent damage when the unit is handled frequently. This type of freezer, in various sizes, can be mounted in a variety of vehicles. The cabinet provides for economical operation that can pay for itself in dry ice savings alone. The unit is plugged in at night. The smaller units rely upon insulation to hold the cold air. Other units plug into the vehicle’s battery.

Small trucks can be fitted with portable freezers. These are useful to dairies servicing school cafeterias and other large food-dispensing operations where milk must be kept cool and ready for servicing at a specific time. Some units can handle between 400 and 700 bottles or cartons of milk. They can be rolled into a cafeteria line.

Written by sam

February 7th, 2011 at 3:07 am

Freezer Refrigerant Leak Testing

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If the system is diagnosed as short of refrigerant and has not been recently opened, there is probably a leak in the system. Adding refrigerant without first locating and repairing the leak, or replacing the faulty component, would not permanently correct the difficulty. The leak must be found.

Sufficient refrigerant may have escaped to make it impossible to leak test effectively. In such cases, add a 1/4-in. line-piercing valve to the compressor process tube. Add sufficient refrigerant to increase the pressure to 75 lb/in.2. Through this procedure, minute leaks are more easily detected before the refrigerant is discharged from the system and contaminates the surrounding air.

The line-piercing valve should be used for adding refrigerant and for test purposes only. It must be removed from the system after it has served its purpose. Braze a 4 in. piece of in. OD copper tube into the compressor process tube. Evacuate the system and recharge after repairs are completed.

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February 7th, 2011 at 2:50 am

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Restricted Capillary Tube

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The capillary tube is restricted when the flow of liquid refrigerant through the tube is completely or partially interrupted. Symptoms are similar to those of a system that has lost its refrigerant. However, the major part of the refrigerant charge will be pumped into the high side (condenser), the same as with a moisture restriction. The suction pressure will range slightly below normal to very low (2 to 20 in. vacuum), depending on the amount of restriction.

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February 7th, 2011 at 2:46 am

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Overcharge of Refrigerant

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When the cabinet is pulled down to temperature, an indication of an overcharge is that the suction line will be cooler than normal. The normal temperature of the suction line will be a few degrees cooler than room temperature. If its temperature is much lower than room temperature, the unit will run longer because the liquid is pulled beyond the accumulator into the heat exchanger. When the overcharge is excessive, the suction line will sweat or frost.

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February 7th, 2011 at 2:45 am

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Complete Recharge of Refrigerant

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In the case of a major refrigerant leak that is repairable, such as a broken or cracked refrigerant line in the machine compartment, the unit will run. However, there may be no refrigeration or only partial refrigeration. Suction pressure will drop below the atmospheric pressure. Thus, with a leak on the low side, air and moisture are drawn into the system, saturating the filter drier. If there is reason to believe that the system contains an appreciable amount of moisture, the compressor and drier filter should be replaced. The system should be cleaned with liquid refrigerant and evacuated, after the leak has been repaired.

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February 7th, 2011 at 2:41 am

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Installing Freezer Drier Coil

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Install the drier coil in the U-channel as shown in Fig. 13-21. Secure the drier coil to the outer shell with short strips of mastic sealer spaced approximately 6 in. apart.

Thread the drier-coil wire leads down through the wiring harness grommet in the lower right-hand front corner of the freezer U-channel. Route the wire lead to the rear of the machine compartment and splice into the service cord.

Install a length of mastic sealer, supplied with the drier coil, on the lower front flange and up to 2 in. on each side of the freezer liner. Install the bottom coldban trim and press the rear edge firmly into the mastic sealer. Then, install the remaining cold-ban trim section.

All chest models have the wrapper-type condenser attached to the inner surface of the cabinet’s outer shell. The condenser, encased with foam insulation, is not accessible for repair.

When there is evidence of an internal refrigerant leak, the evaporator (low side) and condenser (high side) should be disconnected from the system and individually pressurized and leak tested.

A refrigerant leak found in any part of the internal wrapper-type condenser (including the precooler of the freezer) can be repaired by installing an external natural draft-type condenser on the rear of the freezer. Remember that the condenser outlet line must be positioned so that it has a gradual slope downward from the point it leaves the freezer to where it enters the drier. The filter drier must be vertical or at a 30° to 45° angle, with the outlet end down so that a liquid refrigerant seal is maintained.

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February 7th, 2011 at 2:36 am

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Repairing Freezer Condenser

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When a refrigerant leak is found in any portion of the internal wrapper-type condenser (including the precooler) on models with removable liners, the condenser must be repaired. See Fig. 13-20. On the foam-insulated models, an external natural-draft condenser is installed on the rear of the freezer.

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February 7th, 2011 at 2:31 am

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Replacing Freezer Compressor

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With a relatively small amount of refrigerant used in the freezer, the oil in the compressor will absorb a major portion of it when the freezer has been inoperative for a considerable length of time. When opening the system, use care to prevent the oil from blowing out with the refrigerant.

When replacing a compressor on a freezer that is in operation, disconnect the service cord from the electrical outlet. Allow the low side to warm up to room temperature before removing the compressor. Placing an electric lamp inside the cabinet will help raise the temperature.

The procedure for replacement of the freezer compressor is the same as that for the refrigerator compressor.

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February 7th, 2011 at 2:27 am

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Freezer Evaporator Coil

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Liquid refrigerant flows through the capillary tube and into the evaporator coil where expansion and evaporation of the refrigerant takes place. The evaporator coil (low-side) is a pattern of zigzag passes of tubing. The evaporator coil is designed to produce adequate refrigeration and maintain uniform storage temperatures throughout the cabinet. See Figs. 13-18 and 13-19.

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February 7th, 2011 at 2:23 am

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Freezer Wrapper Condenser

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All compressors have internal spring suspension with four point external mounting. The compressors have plug-in magnetic starting relays. These mount directly over the compressor Fusite terminal assembly and a separate motor overload protector.

The wrapper condenser incorporates a precooler condenser in series with the main condenser. A wrapper condenser depends on the natural convection of the room air for dissipation of heat.

The high-temperature, high-pressure discharge refrigerant vapor is pumped into the precooler condenser. This is located on the back wall of the freezer where it releases part of its latent heat of vaporization and sensible heat of compression. From the precooler condenser, the refrigerant passes back to the machine compartment and through the cooler coil in the compressor dome (where additional heat is picked up from the oil). It then passes back to the main condenser, where additional heat is released to the atmosphere. This results in condensation of the refrigerant from the high-pressure vapor to the high-pressure liquid.

Ample condenser area is provided to keep the surface temperature of the cabinet only 10 to 15°F (5.5 to 8.3°C) above room temperatures. Heat released by the condenser helps reduce the possibility of moisture condensation on the cabinet surface in humid areas. The wrapper-type condenser eliminates service calls caused by plugged or dirty condensers. For the life of the freezer, the wrapper condenser remains efficient. A filter drier is located in the liquid line at the outlet of the condenser.

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February 7th, 2011 at 2:19 am

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