Refrigerator Troubleshooting Diagram

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Air Conditioning Troubleshooting

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To troubleshoot this type of air-conditioning equipment, a troubleshooting table (Table 15-1) has been provided at the end of this chapter. The general troubleshooting procedures listed in the table are used for hermetically sealed compressors.

Table 15-1 Troubleshooting Hermetic Compressor Type Air-Conditioning Equipment

Trouble Probable Cause Remedy or Repair
Compressor will not start. (No hum.) Open line circuit. Check the wiring, fuses, and receptacle.
Protector open. Wait for reset. Check current drawn from line.
Contacts open on control relay. Check control, and check pressure readings.
Open circuit in the motor stator. Replace the stator or the whole compressor.
Compressor will not start. However, it hums intermittently. Cycles with the protector. Not wired correctly. Check wiring diagram and actual wiring.
Line voltage low. Check line voltage. Find where line voltage is dropped. Correct.
Start capacitor open. Replace start capacitor.
Relay contacts do not close. Check by manually operating. Replace if defective.
Start winding open. Check stator leads. Replace compressor if the leads are OK.
Stator winding grounded. Check stator leads. Replace compressor if leads are OK.
Discharge pressure too high. Remove cause of excessive pressure. Discharge shutoff and receiver valves should be open.
Compressor too tight. Check oil level. Correct the binding cause. If this cannot be done, replace compressor.
Start capacitor weak. Replace the capacitor.
Compressor starts. Motor will not speed up enough to have start winding drop out of circuit. Line voltage low. Increase the voltage.
Wired incorrectly. Rewire according to wiring diagram.
Relay defective. Check operation. If defective, replace.
Run capacitor shorted. Disconnect the run capacitor and check for short.
Start and run windings shorted. Check winding resistances. If incorrect, replace the compressor.
Start capacitor weak. Check capacitors. Replace those defective.
Discharge pressure high. Check discharge shutoff valves.
Check pressure
Tight compressor. Check oil level. Check binding. Replace if necessary.
Compressor starts and runs. However, it cycles on the protector. Low line voltage. Increase the voltage.
Additional current being drawn through the protector. Check to see if fans or pumps are wired to the wrong connector.
Suction pressure is too high. Check compressor. See if it is the right size for the job
Discharge pressure is too high. Check ventilation. Check for over-charge. Also check for obstructions to air flow or refrigerant flow.
Protector is weak. Check current. Replace protector if it is not clicking out at right point.
Run capacitor defective. Check capacitance. Replace if found defective.
Stator partially shorted or grounded. Check resistance for a short to the frame. Replace if found shorted to ground (frame).
Inadequate motor cooling. Correct air flow.
Compressor tight. Check oil level. Check cause of binding.
3 phase line unbalanced. Check each leg or phase. Correct if the voltages are not the same between legs
Discharge valve leaks or is damaged. Replace the valve plate.
Start capacitors burn out. Short cycling. Reduce the number of starts. They should not exceed 20 h.
Prolonged operation with start winding in circuit. Reduce the starting load. Install a crankcase pressure limit valve. Increase low voltage if this is found to be the condition. Replace the relay if it is found to be defective.
Relay contacts sticking. Clean the relay contacts. Or, replace the relay.
Wrong relay or wrong relay setting. Replace the relay.
Wrong capacitor. Check specifications for correct size capacitor.
Be sure the MFD and WVDC are correct for this
compressor.
Working voltage of capacitor too low. Replace with capacitor of correct WVDC.
Water shorts out terminals of the capacitor Place capacitor so the terminals will not get wet.
Run capacitors burn out. They spew their contents over the surfaces of anything nearby. This problem can usually be identified with a visual check. Excessive line voltage. Reduce line voltage. It should not be over 10% of the motor rating.
Light load with a high line voltage. Reduce voltage if not within 10% overage limit.
Voltage rating of capacitor too low. Replace with capacitors of the correct WVDC.
Capacitor terminals shorted by water. Place capacitor so the terminals will not get wet.
Relays burn out. Low-line voltage. Increase voltage to within 10% of limit.
High-line voltage. Reduce voltage to within 10% of the motor rating.
Wrong size capacitor. Use correct size capacitor. The proper MFD rating should be installed.
Short cycling. Decrease the number of starts per hour.
Relay vibrating. Make sure you mount the relay rigidly.
Wrong relay. Use the recommended relay for the compressor motor.

Written by sam

February 7th, 2011 at 3:32 am

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

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