Refrigerator Troubleshooting Diagram

Archive for the ‘Domestic refrigerators and freezers troubleshooting’ Category

Condensing Unit And Evaporator Not Working

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■     Check the settings on the thermostat. Is unit turned on and is the temperature high enough to be calling for the unit to operate.

■     If unit fails to come on, turn fan control switch of the sub-base to the constant run position. If the fan comes on, low voltage is present in the system. If it doesn’t come on, there is no low volt­age in the system. Check at the transformer for secondary voltage. If not present, check the primary.

No primary voltage —        Check fuse that supplies the unit.

No secondary voltage —    Bad transformer.

Both primary and secondary voltage present – Check at sub-base of thermostat for 24 volts.

Voltage present at sub-base — Replace sub-base and thermostat.

Voltage not present at sub-base — Control wiring from transformer to thermostat defective.

Written by sam

November 15th, 2019 at 8:38 am

Refrigerator Blown Fuse

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Use ohmmeter first to check unit continuity ground.

In checking for a ground in either section, power supply disconnects should be open. This prevents any accident from occurring due to a feed back of power. There are times when only one fuse opens letting electricity flow through the good fuse. With disconnect open, check from the load side of the circuit being tested. In the case of the condensing unit, check the compressor contactor. If a ground is indicated, all of the circuits must be isolated including the compressor, condenser fan motor, crankcase heater, and any other electrical device that may be wired to the unit. This also applies to the evaporator section when it is tested.

At times, a ground can develop in the supply circuit itself that would cause the circuit to open. In cases like these, your responsibility is over. The electrician should be notified that you are to be informed when the power supply circuit is repaired.

The third reason for power supply to open is an overloaded circuit. The demand exceeds the rating of the protection device.

Written by sam

October 5th, 2011 at 9:28 am

Not Cooling Enough Ice on Suction Line

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Turn unit off immediately so it can defrost.

Insufficent air passing through evaporator coil—Check for restriction, dirty evap­orator coil, or filter.

■   After the unit is defrosted, and this might be the following cooling enough on hot days. The reason is a structure requiring a three-ton unit is being cooled by a two-ton unit due to the inefficient compressor.

Written by sam

August 18th, 2011 at 9:27 am

Compressor Burn-Out

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The first thing you must establish in changing a compressor was the nature of the failure. Of course if it was a mechanical problem such as a broken connecting rod, the changing of the compressor is relatively simple. In the case of an electrical failure, the clean-up is rather specific. Many times a service company can’t seem to keep a compressor operational in a certain installation. The reason is the improper procedure was followed.

The severity of the burn-out is apparent sometimes when the refrigerant lines are bled. The stench of burned refrigeration oil is unmistakably pungent. Exercise extreme caution in regard to the exhausting vapor; keep if from your skin and eyes. In Chapter 14 you were told about the acid formation in refrigeration systems. Always assume the oil has acidity, and you won’t get into any trouble.

When the system pressure is equalized with the atmosphere, begin taking the compressor loose from its mountings and piping. Assume nothing, spill some oil from the old compressor into a clean jar. Perform an acid test with the acid kit. The directions come in each kit. Even when there is not a foul smell to the refrigeration oil, acid still could be present in the system. If this is not done and acid is present, the insulation on the new compressor’s winding will be attacked and destroyed causing electrical failure. The time be­tween the installation and the failure is governed by the concentration of acid in the oil.

The number one thing to do is rid the system of the acid. On most commercial units using a semi-hermetic compressor changmg oil is comparatively easy. There are two schools of thought about acid clean-up in a system. One is to change the suction line filter driers often, and the other is change the oil often. I’ve found that changing the oil and the filters is the only way to do a thorough job. Oil acts like a sponge soaking up moisture and acid. It might take several oil changes with several hours of compressor running before all traces of acid are removed.

In some commercial units, when the evaporator coil is lower than the condensing unit, it helps to place a drain valve in the lowest point of the coil. This valve is used to release any oil that might be trapped in the evaporator. With the new compressor in operation,

the oil level milflt be AeM and IWHlflht tfl tllfi WW M TlUS is done on most semi-hermetic compressors with the crankcase sight glass.

When working on a hermetic compressor installed in a residence, the clean-up procedure is somewhat different. All manufacturers of compressors place an oil charge in the compressor when it is shipped from the factory. The compressor you are to change also has a factory oil charge in it. Oil amounts measured in ounces is not very much, yet a few more ounces than needed can create problems in a compressor. For this reason, care must be taken to measure the amount of oil reclaimed during the compressor change out.

I carried a kitchen measuring cup with a 32-ounce capacity. When the compressor was removed from the cabinet of the unit, I would pour the oil from the compressor into the measuring cup. If a compressor had a 14-ounce capacity, and only eight ounces were in the cup, six ounces were still in the system. With the use of nitrogen enough pressure can be placed into and through the piping to remove the sue ounces. R-12 refrigerant can also be used as a flushing agent to remove contaminated oil from the system.

After all of that, install a suction line drier filter. In most cases, residential units were not equipped with them. Some have liquid line driers. If the unit you are working on has a liquid line drier on it, change it and then install a suction line drier. I also recommend the use of flare fittings on the suction drier, if possible. The suction line drier should be changed after running in the unit for a few days. There should be about 40 hours running time on the filter. Of course this is only an average. Clean-up of a real bad bum requires that the fil­ter drier be changed after several hours of initial start-up of the new compressor.

It is difficult to get an oil sample from a small hermetic residential unit. For this reason, make your clean-up a proper one. Oil can be felt in the hot gas of the discharge line. This oil should only present itself in a vaporized mist. If it is experienced as oil droplets, the system has an overcharge of oil in it. This is a situation that can cause problems with the compressor, depending upon the amount of the excessive oil. The only way to remove some of it is by letting it escape from the discharge line. Of course this method requires you to top off the charge before you leave the unit.

Acid test kits are a valuable tool and not used enough by many technicians. In many commercial preventive maintenance programs that you implement, it should become standard procedure to take an acid test of a unit once a year. In many cases, a compressor could be saved by an oil change. When acid starts to form, but is removed before attacking the motor windings of the compressor, it does no harm. Years ago, an acid sight glass was used on large commercial units. This sight glass had a fine piece of copper placed where the moisture indicator is. When the service technician checked the refrigerant level in the sight glass, he was also able to see if any deterioration was taking place with the fine copper wire. If so, it alerted him to start a neutralization program. He immediately instituted oil changing keeping a constant eye on the acid sight glass to see if it progressed or ceased. I’ve not seen this type sight glass in parts houses for a long time. Stopping things before they happen is a big part of your job. A few drops of grease or oil in a motor bearing stops a growl, and prolongs the life of the motor.

Written by sam

December 24th, 2010 at 9:43 am

Unit Stop Operation

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This can present a problem due to the automatic reset controls found on most residential and light commercial units. During a malfunction, a control opens and stops the unit’s operation. By the time you drive across town, the safety control has time to reset.

Flagging is done. Flags are sold at most supply houses. Let me explain to those that might never have used them. The flag is de­signed to conduct very small amounts of electricity. It will open like a fuse if a high ampacity load is placed across it. The flags are wired across every control in parallel. In the event the control opens, the flag will open and indicate. I’ve found that small ampacity type automotive fuses and holders work as well and are less costly. When flagging a unit, don’t place flags on controls that are supposed to open such as the low pressure control of a pump-down system. Only flag the actual safety controls. With the use of this method, you at least find out what part of the system is the problem area.

Written by sam

December 24th, 2010 at 9:30 am

Condensing Unit And Evaporator Section

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There are times when everything appears to be operating according to all specifications, yet, insufficient cooling is the

Heat strips energizing with cooling-Check the heat relay in the air handler and see if there is 24 volts being applied to the holding coil.

The resistive heaters would counteract the cooling effect. Sometimes the contacts of a heat relay weld in the closed position, causing this. If 24 volts are found at the relay when the thermostat mode is in cooling, you must check the system circuitry. Disconnecting for the summer is alright; however, you will have to isolate the problem sooner or later. The source should be found in the evaporator section. It is either receiving its voltage from the thermostat or the defrost device in the condensing unit, if it is a heat pump. Sub-bases are sometimes the blame. They distort on an uneven wall surface causing them to crack or short circuit.

Written by sam

December 24th, 2010 at 9:11 am

Evaporator Section Blowing Hot Air

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Check condensing unit to see if it is operating. Place one hand on the liquid line and the other on suction line. If the condenser fan is operational and there isn’t any difference in the temperature of the two lines, the compressor is not operating. If the fan motor is not operating, check for line voltage and low voltage in the control panel. You must establish if the problem is in line voltage or low voltage. If line voltage is present, and there is no low voltage, nothing will operate.

No line voltage—           Check fuses for the supply voltage to the condensing unit.

No low voltage—               If present through the thermostat, a wire from the thermostat to the condensing unit is open.

tests can be made over a period of time. In the above case, the pressure recorder hooked to the high side of the system. The amperage recorder should be hooked to the condenser fan motor power supply. Each time the compressor cycles on, the pressure is recorded on a chart similar to those used in the medical profession. Everytime the compressor cycles so should the condenser fan motor. The defective motor will stop operating and thus the amperage will either fall to zero or climb to locked rotor and fall. This would be followed by the high pressure side of the system starting to elevate. This is truly the only way to solve a situation such as this.

Written by sam

December 24th, 2010 at 8:57 am

Domestic Absorption System

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The modern domestic absorption refrigerator or ‘gas refrigerator’ operates on the principle of using heat to produce cold. It employs a mixture of hydrogen and ammonia with water (aqua-ammonia) as the cooling agent: water has an affinity for ammonia, and the hydrogen speeds up the process of evaporation.

Absorption system cycle

Absorption system cycle

The heat source may be town gas or, in the case of smaller systems designed for use in caravans, camp sites etc., propane, butane or even paraffin. An all-electric version has a small heater element to provide heating.

The valve assemblies which regulate the gas flow incorporate a small pilot jet to ignite the gas, as the valve is energized electrically. The evaporating temperature is controlled by a thermostat which in turn energizes the gas valve or heater element, depending upon the setting of the thermostat (cold control).


When the thermostat energizes the valve or heater, heat is applied to the ammonia and water mixture in the generator. The liquid then boils off the pass through a small tube (percolator tube), in much the same way as coffee in a percolator, to enter the separator or rectifier. From there it circulates by gravity.

The ammonia vaporizes faster than the water and the aqua-ammonia separate in the rectifier; the ammonia vapour rises to the condenser and the water drains back to the absorber to be recirculated. The lighter ammonia vapour rising from the condenser coils changes back to a liquid to drain into the evaporator, where it mixes with the hydrogen vapour from the absorber.

Heat from the stored product in the food compartment of the refrigerator will vaporize the ammonia liquid in the evaporator. The mixture of ammonia vapour and hydrogen, being heavier than either of the two gases alone, passes to the absorber where it meets the water coming from the rectifier. The ammonia is then absorbed by the water and, when the water has absorbed as much vapour as it can hold, the vapour returns to the evaporator.

At maximum working conditions (maximum heat at generator) the pressure on the high side of the system (condenser and absorber) will be approximately 14 bar with a relative temperature of 360 C Assuming that the refrigerator is in an average ambient temperature of 210 C the heat rejection will be quite reasonable with a 150 C temperature (36-210 C Pressure on the low side of the system will be 12.6 bar hydrogen and 1.2 bar ammonia, so the relative temperature of the evaporator will be – 150 C At this temperature, heat exchange from the food products to the evaporator will be at an average 30 producing a 12o C temperature difference [ 3 to – 15 = 120 C ]


Since this is a completely sealed system containing two gases, very little can be achieved by the service engineer except the replacement of a thermostat, valve assembly or heater element.

The pilot jet and valve should be kept clean and the refrigerator should be carefully levelled at the time of installation and checked when service is carried out.

Figure 65 shows the absorption system cycle.

Refrigerant Charging in Domestic Appliances

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Domestic refrigerators and freezers operate with very small refrigerant charges, and the charge must be administered accurately. This can be best achieved by using a visual charging cylinder, sometimes called a dial-a-charge (Figure 64).

This is basically a small refrigerant cylinder with a liquid-indicating sight glass or tube. In front of the sight glass and surrounding the cylinder and sight glass is a rotating screen upon which are graduated scales for the common refrigerants, RI2, R22 and R502. Above the refrigerant scales is a temperature range.

Fitted to the top of the cylinder assembly are a pressure gauge; a purging valve, which is normally a Schraeder type; and, if a heater is incorporated, a pressure relief valve for the cylinder protection. At the base of the cylinder is a charging valve and hose connection.

Visual charging cylinder

Visual charging cylinder

Filling the cylinder

1. Obtain a service cylinder of the correct refrigerant. Connect it to the visual charger with a suitable hose.
2. Open the valve on the service cylinder and invert the cylinder.

3. Slacken the hose connection at the charging valve to purge air from the hose. Tighten the hose connection.
4. Open the charging valve to allow refrigerant liquid to flow by gravity into the cylinder. Observe the sight glass: when liquid flow ceases, depress the purge valve and gently vent off a small amount of refrigerant vapour. When a pressure difference between the charging cylinder and the service cylinder is created, the liquid will begin to flow again. Repeat this operation until the required amount of refrigerant is in charging cylinder.
5. Close the valves on both the visual charger and the service cylinder.
6. Disconnect the service cylinder.

Charging the system

1. Assuming a line tap valve has been installed and the system evacuated, connect the hose to the charging valve and the line tap valve.
2. Open the charging valve and slacken off the hose connection to purge air from the hose. Close the valve.
3. Note the ambient temperature. Rotate the screen until the required refrigerant scale lines up with the ambient temperature on the temperature scale.
4. Note the level of the refrigerant in the sight glass.
5. Open the line tap valve fully and slowly meter the prescribed amount of refrigerant into the system. If the visual charger has a heater this can be energized before opening the line tap valve to create a pressure difference between the charging cylinder and the system.
6. When the charge has been administered as indicated by the sight glass, close the charging valve.
7. Allow a few minutes for the liquid in the hose to vaporize and the system pressure to equalize. Then close the line tap valve.
8. Disconnect the visual charger and leak test the system.

Alternative method of charging

If a refrigerant charge cannot be accurately measured by using a visual charger, it must be drawn into the system by the compressor from the low side. It is imperative that this is carried out slowly to eliminate the risk of overcharging, which could damage the compressor.

By allowing small amounts of refrigerant vapour into the system, and observing the frost line on the evaporator, overcharging can be prevented.

When the frost line reaches the location of the thermostat bulb it is always advisable to stop charging and allow sufficient time for the system to reach average evaporating temperature and start to cycle. Should frosting back occur, purge off the surplus refrigerant in small amounts from the line tap valve connection.

Reference to the compressor nameplate should be made to determine the running current.

Refrigerant charges are normally stamped on the refrigerator model plate. The charge may be given in ounces or grams according to the age of the refrigerator. These quantities can be easily converted: 1 ounce = 28.35 grams. For example, 150 grams is equivalent to 150/28.35 = 5.29 ounces; 6.5 ounces is equivalent to 6.5 x 28.35 = 184.27 grams.

Remember, an undercharge of refrigerant will result in long running periods or continuous running. An overcharge of refrigerant will result in frosting back, overheating, increased running costs and could possibly damage the compressor.

Domestic Refrigerator Electrical Faults

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The diagnosis of electrical faults on components and compressors has already been dealt with in previous articles. The following procedure may be carried out to quickly pinpoint the faulty component and to eliminate unnecessary dismantling. The electrical circuit is tested for continuity from the terminal board of the circuit. The typical electrical circuit in Figure 61 has been chosen for the test procedure.

Steps 1 and 2 of the test procedure can be disregarded if the refrigerator or freezer has an interior light. This will come on when the appliance door is opened, unless the light bulb itself is defective.

Domestic appliance circuit testing

Domestic appliance circuit testing

The procedure is as follows:
1. Test for continuity from points 1 to 2, which will test the whole circuit.
2. Test from point 3 to points 1 and 2 to reveal any earth fault.
3. Test from points 1 to 8, which eliminates half of the circuit.
4. If the fault is in section 1 to 8, test between points 1 and 5 to determine if the fault is due to a loose connection, a defective cable or a blown fuse.
5. Should the fault be located in section 5 to 8, then the thermostat must be considered inoperative because the interior light and door switch will be isolated when the door is closed.

6. If the fault is in the compressor half of the circuit, it should be located in a similar manner by dividing into sections until it has been finally determined.

When an ohmmeter is used to test for continuity, it should normally be set to read off the x 1 scale. If the total resistance of the circuit is in excess of 100 ohms, the x 10 scale will be required; reset to the x 1 scale when the faulty section is isolated to less than 100 ohms.

Figure 62 shows a typical refrigerator/freezer electrical circuit.

Typical refrigerator~freezer electrical circuit

Typical refrigerator~freezer electrical circuit