Refrigerator Troubleshooting Diagram

Archive for the ‘Refrigerator Repair’ tag

Refrigerator Check valve

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This is sometimes called a non-return valve. It is a simple device used to ensure that fluid or vapour can only travel in one direction and not back up to another part of the system pipework. Check valves have been mentioned in connection with oil separators (Figure 75), multiple evaporators (Figure 84) and hot gas defrosting (Figures 86a and 86b).

Figure 87 shows the construction of the valve, and the locations in a multiple evaporator system.

Check valve construction and location

Check valve construction and location

 

Written by sam

November 12th, 2009 at 10:45 am

Refrigerator Crankcase Heater

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This is a resistance heater. If externally mounted it is located on the underside of the compressor crankcase. It may be mounted internally as an integral part of the compressor; this is standard for larger commercial equipment.

The presence of liquid refrigerant in a compressor crankcase is wholly undesirable. It could cause dilution of the lubricating oil, resulting in poor lubrication. Liquid refrigerant vaporizing in a crankcase will cause foaming when the compressor operates after an off cycle. Excess oil will then be discharged by the compressor; this could drastically reduce the amount of oil in the crankcase. Non-condensible slugs of oil and liquid refrigerant could enter the compressor cylinders to cause considerable damage to valves, pistons and connecting rods, and even to fracture crankshafts.

Crankcase heaters are essential for compressors installed for low temperature applications, where evaporating temperatures and crankcase temperatures can be extremely low. They are also necessary for remote installations where the compressor is exposed to low ambient temperatures (winter conditions). Whenever the crankcase temperature falls below that of the evaporator, refrigerant vapour will migrate and condense in the crankcase unless a heater is employed to maintain a temperature in the crankcase above the temperature of the refrigerant vapour.

Because of the tendency of oil to absorb miscible refrigerant, a certain amount of refrigerant will always be present in the crankcase.

Written by sam

November 12th, 2009 at 10:43 am

Refrigerator Solenoid Valve

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This is an electrically operated magnetic valve. It consists of a coil wound around a sleeve of non-magnetic substance. When energized, the coil carries an electrical current and becomes a magnet.

Inside the sleeve is a movable iron core, which will be attracted by the magnetic field of force to remain suspended in a midway position inside the sleeve. The iron core movement opens the valve. When the coil is de-energized, the iron core returns to its normal position to close the valve.

This type is normally closed. Others are available which are normally open; these close when the coil is energized.

Some solenoid valves have flare fitting unions, whilst others are brazed into position. It is important that the coil is removed when brazed joints are made. For optimum operation the valve should be installed in an upright position and rigidly mounted; the valve should never rely on the system pipework for support.

There are many uses for this type of valve, such as in defrost systems, multiple evaporator systems and pump-down cycles. In effect, it is used wherever it is necessary to stop the flow of refrigerant to a specific section of pipework on a particular application.

Written by sam

November 12th, 2009 at 10:41 am

Refrigerator Three Phase Electrical Connections

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Smaller compressor motors incorporate overload protectors, either internally or externally mounted, and use various small starting devices. By contrast the three phase motor, being larger, requires more sophisticated methods of automatic starting and overload protection, provided by contactors or starters.

Contactors and starters

A contactor is a power operated switch suitable for frequent making and breaking of an electrical circuit. A starter is a power operated switch with inbuilt overcurrent features, employed for starting a motor and protecting it during running. Both controls enable large currents to be switched by means of a system control (thermostat) with low current rating.

Suppliers of these controls are numerous. Each has its own options with regard to overload protection, single phasing protection and accessibility for component replacement. Wiring diagrams for the controls are normally supplied or are available on demand. These should be referred to before any attempt is made to install, make electrical connections to or diagnose faults on the controls. Because of the different types of control, only typical examples are dealt with here. Figure 104 shows connections for single phase starting, and Figure 105 shows a particular three phase starter.

single-phase-starter

types-of-three-phase-starter

Direct-on-line starter

With the standard squirrel cage induction motor, it is advantageous to have DOL starting. This allows a cheaper motor starter and control gear to be used, and also imposes less strain on motors during starting.

However, electrical supply authorities will normally restrict starting currents. DOL starters should only be specified for motors within the supply authority limits.

Figure 106 shows the electrical connections for three phase DOL starters.

three-phase-DOL-starter

three-phase-DOL-starter-2

Written by sam

November 12th, 2009 at 4:37 am

Refrigerator Fusible Plugs

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Note: Before charging a system with a new or replacement refrigerant check the fusible plug rating.

Condensers and receivers are fitted with fusible plugs. These are safety devices against excessive high side pressures developing in the event of a fire. (Excessive operating pressures are controlled by the high pressure cut-out switch) The plugs are normally brass studs with a 3 mm hole drilled through the centre, which is filled with a low melting point solder.

It is important that, when a replacement is fitted, the correct plug is selected. The following are the required melting points for various systems:

R12     1000 C (2100 F
R22      760 C (1700 F)
R502   760 C (1700 F)
R717   680 C(1550 F)

Written by sam

November 11th, 2009 at 8:55 pm

Refrigerator Reversing Valve

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This type of valve is in common use for hot gas defrost systems and room air conditioners. It effectively reverses the flow of refrigerant to the evaporator and condenser when a defrost period is initiated. In room air conditioners, it reverses the flow when heating is required rather than cooling.

The valve is an electromagnetic type and operates by pressure when the solenoid is energized. Figure 86a shows how the valve is installed. When installation of the valve requires brazing, always remove the solenoid coil (which is detachable) and wrap a wet cloth around the valve body to avoid damaging the valve mechanism when intense heat is applied.

refrigerator-reversing-valve

refrigerator-reversing-valve-system

Written by sam

November 11th, 2009 at 8:50 pm

Refrigerator Water Regulating Valve

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The pressure operated type is the most popular. It is employed in water cooled systems to control the flow rate through the condenser, modulating in response to changes in the condensing or operating head pressure.

It is designed to stop the flow of water to the condenser when the plant is at rest. An increase in the head pressure will open the valve to allow a greater volume of water through the condenser. A decrease in head pressure will automatically reduce the volume of water flowing through the condenser.

The location of the valve may vary; it may be installed at the inlet to the condenser or at the outlet. Current practice is to install it at the condenser outlet, to ensure that the condenser does not drain when throttling takes place during operation and normal modulation of the valve. Figure 85 shows the valve installed in both positions.

The valves are adjustable. As a guide to operating conditions, the valves should be adjusted to maintain a temperature difference of 7-9o C (15-180 F) between the inlet and the outlet water.

refrigerator-water-regulating-valve

Written by sam

November 11th, 2009 at 8:48 pm

Refrigerator Evaporator Pressure Regulator

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This valve is fitted in the suction line to control the pressure in the evaporator, to prevent it dropping below a predetermined pressure. It is used to control the evaporating temperatures of systems such as drinking water fountains and beverage coolers, to maintain a constant evaporator pressure/temperature and prevent freezing.

It is also used in multi-evaporator systems, when it is installed in the suction line of the warmest evaporator. Check valves or one-way valves are necessary to prevent migration of refrigerant from the warmer to the cooler evaporators during off cycles (see Figure 84).

refrigerator--check-valve

Written by sam

November 11th, 2009 at 8:45 pm

Refrigerator Crankcase Pressure Regulator

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As a compressor starts, a heavy load is imposed on the drive motor. The crankcase pressure will be at its highest against normal or abnormal loading.

The function of the regulator is to keep the pressure in the crankcase to a reasonable level to protect the motor from overload. This applies when the evaporator pressure is above normal operating pressure, for example:

1. During the initial start-up after defrosting.
2. During periods of high starting loads.
3. Under high suction pressure caused by hot gas defrosting.
4. During surges in suction pressure.
5. Under prolonged high suction pressure.

The regulator is installed in the suction line as shown in Figure 83.

Location of crankcase pressure regulator

Location of crankcase pressure regulator

As a guide, the control should be set to the following crankcase pressures:

Hermetic and semi-hermetic compressors:         2.5 bar
Open-type compressors with standard motor:   3.0 bar
Open-type compressors with oversized motor:  4.5 bar.

Final adjustments are made to make the running current

Written by sam

November 11th, 2009 at 7:27 pm

Refrigerator Pipework Assembly

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Soft copper tubing up to 22 mm (7/8 in) diameter may be joined with flare fittings or by brazing. Hard drawn copper tubing is brazed. Iron and steel pipework is welded; cost restricts the use of welding to large industrial and ammonia systems, and it is not described here.

Flare fittings

Flare connections will be perfectly satisfactory if the flaring of the tubing is carried out correctly.

Undersized or oversized flares are potential sources of leaks. In an undersized flare the flare seat surface area is reduced and can allow movement within the flare fitting if the pipework is subjected to excessive vibration; the joint will eventually fracture. An oversized flare may prevent the correct seating to a union or a control; although it may well pass a leak test, a leak may develop when the pressures within the systems rise during operation. Flares are shown in Figure 80.

A good flare should allow withdrawal of the flare nut over the threads after it has been tightened down on to a union.

copper-tube-flaring

Brazing

Currently, most copper tubing is assembled with brazed joints because it is cheaper. In addition, if joints are made correctly the possibility of leaks is reduced.

In order to make a brazed joint the tubing has to be expanded. Various tools are available for this purpose: the punch-type expanders, swage formers used with a flare block and spinner, and the more elaborate tube expander.

The tube expander is generally used for larger diameter tubing, which may be hard or soft drawn copper. Hard drawn copper must be annealed before attempting to expand the tube. Annealing is a softening process, involving heating the tube and allowing it to cool.

When using a swage former or the expander, the depth of the swage will be determined by the former. It is approximately equivalent to the outside diameter of the tubing. Too shallow an expansion of the tube tends to produce a weak joint (see Figure 81).

copper-tube-swaging

Process

Brazing can be defined as jointing by applying high intensity heat to a high melting point alloy in order to fuse together two metal surfaces. It is often referred to as silver soldering.

Brazing rods should be cadmium free, and as described in BS 1845. All brazing should meet the requirements of BS 1723.

Hazards

Whilst it is possible to prefabricate some parts of the system pipework assembly in workshops, most brazing will be carried out on site.

The operator must be conversant with the site safety regulations and comply with fire regulations. Attention must be paid in particular to fire and smoke alarms whilst the brazing operations are being performed.

Where possible, work away from flammable materials such as wooden floors, joists and eaves. Use a protective metal or fire resistant sheet under conditions where a fire risk is obvious. Keep a fire extinguisher to hand when working in a risk area.

The number of brazed joints should be kept to a minimum, and the bending of copper tubing is preferred.

Preparation

All pipework and fittings to be brazed must be cleaned to remove dirt and oxides using a fine grade steel wool. A solvent may be necessary to remove preservative coatings from components or fittings.

Heat shields should always be used to protect areas surrounding the joint and to concentrate heat. Protect the system components, which could suffer damage when heat is applied, by wrapping a damp cloth around the component close to the joint.

Ensure that all joints are a tight fit. Support the pipework before brazing is attempted; any movement before the alloy has set can result in a leak or a weak joint.

Equipment usage

Select the correct pressure and nozzle (Table 5). Always light the blowtorch with a spark gun and not with matches or a cigarette lighter. Adjust the blowtorch to give the correct type of flame (see Figure 82).

Wear protective clothing and tinted goggles or glasses. Keep oxygen and acetylene cylinders away from any heat source. Always close down the equipment valves when leaving it unattended, even for a short period. Do not smoke when brazing. Note that toxic atmospheres are created during brazing operations when cadmium, galvanized metal and paint are heated.

Always pass nitrogen through the pipework or component being brazed to prevent oxidation and the formation of scale on the interior surfaces. Clean off all joints after brazing, especially when a flux has been used.

table-5

When brazing copper tubing, the joint area should be heated broadly with a continuous circular movement of the blowtorch until the copper changes colour to a cherry red; then apply the brazing rod. This will minimize the risk of local overheating and burnt tubing. Heat should be applied indirectly so that the rod and flux are melted by conduction through the base metal.

brazing-flame

Written by sam

November 11th, 2009 at 7:01 pm