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Diagnostics of malfunctions of an air conditioning system

Diagnostics of malfunctions of an air conditioning system 1
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Diagnostics of malfunctions of an air conditioning system

Diagnostics of malfunctions of an air conditioning system

COOLING PROBLEM?

The most common cause of problems with the cooling system is the lack of refrigerant in the system. If refrigerant leaks through a leaking compressor or O-ring, leaks through a micro-hole in an evaporator or condenser, or through an unpressurized hose, the leak must be located and repaired before replenishing the system with refrigerant.

In many systems, the compressor is not activated when the refrigerant level is low, as the low pressure alarm switch prevents the compressor clutch from engaging at low pressure. This helps protect the compressor against possible damage caused by insufficient lubrication..

The first step is to check the compressor: if the electromagnetic clutch of the compressor is not activated when the air conditioner is turned on, the problem may be a blown fuse or damaged wiring. Replacing a blown fuse can temporarily restore the air conditioner, but first of all, it is necessary to determine and correct the root cause of this malfunction, so that this does not happen in the future.

If the electromagnetic clutch receives power but does not turn on the compressor, then this clutch is defective and needs to be replaced. If there are signs of leakage around the compressor shaft seal, the seal must also be replaced..

If the clutch is in working condition, but does not turn on the compressor (and the belt creaks in protest), then the compressor has served its age and needs to be replaced.

Compressor failure is usually the result of a loss of lubricant supply, which in turn is due to a low level of refrigerant in the system, clogging (for example, a clogged throttle tube prevents refrigerant and oil from entering the compressor), loss of lubricant due to leaks, or unsatisfactory maintenance (if no oil is added to the system to recover oil that was lost due to leakage or component replacement) or using the wrong type of grease.

R-12 refrigerant systems use mineral oil, while R-134a systems require polyalkylene glycol (PAG) or polyester (POE) oil. The use of mineral oil in modern systems operating on R-134a can cause serious problems with the supply of lubricant, as well as the use of polyalkylene glycol oil of the wrong grade (viscosity). Always follow the recommendations of car manufacturers or lubricant manufacturers on the use of compressor oil.

The next thing to check when diagnosing a malfunction of the cooling system is the pressure in the system. For this you need a set of pressure gauges. Connect your pressure gauges to low and high pressure fittings. If both manometers – on the high pressure side and on the low pressure side – give low readings, then the refrigerant level in the system is insufficient and the system needs to be replenished.

AIR CONDITIONER MALFUNCTION: REFRIGERANT LEAKS

Cooler leaks through microscopic pores in the hoses are common in all cars. The older the car, the greater the rate of seepage. New cars have good seals and hoses, which, as a rule, only allow a few grams of refrigerant per year. However, the capacity of the system in new cars is usually less, so any refrigerant leak has a stronger adverse effect on cooling capacity..

Different methods can be used to check for leaks. Typical oil stains indicate leaks in older R-12 refrigerant systems, but in more modern R-134a systems they are less noticeable since polyalkylene glycol oil (PAG) is not as greasy as mineral oil, so in the second case it is more difficult to see the leak.

Leaks can be detected by adding dye to the system (sold pre-mixed with refrigerant in sealed containers), using an electronic leak detector, or just using soapy water (add refrigerant to the system, turn on the air conditioner, spray hose connections with soapy water and look for bubbles). If you find a leak, you need to fix it before replenishing the system with refrigerant. Typically, repairing leaks involves replacing o-rings or hoses, but if an evaporator or condenser leaks, repairs can be expensive..

LOW COLD PERFORMANCE

Diagnostics of malfunctions of the cooling system is carried out by connecting pressure gauges to valves of low and high pressure. Although poor cooling is often associated with low refrigerant levels in the system, other factors can also affect this (see table)..

Low pressure side High pressure side Temperature in the pipeline Possible reason
Low Low Warm Low refrigerant
High High Warm Excessive refrigerant level
High High Cool System air or excess refrigerant
Normal Normal Warm Warm Moisture in the system
Low Low Warm Expansion valve stuck closed
Low Low Warm Throttle clogged
Low Low Warm High pressure side interference
High Low Warm Defective compressor or control valve

How to determine if your air conditioner needs a refrigerant: check the LOW pressure gauge when the engine is off. At an ambient temperature of 25 degrees Celsius, the LOW pressure gauge should reach about 56 psi (psi) or higher if the air conditioning system contains enough refrigerant. At an ambient temperature of ≈32 degrees Celsius, the LOW pressure gauge should reach about 70 psi or higher. If the LOW pressure gauge is lower than indicated, the air conditioning system needs to be charged with refrigerant.

For information on the normal operating pressure and refueling capacity of the system, see the automaker’s specifications. In modern passenger cars, air conditioning systems are designed for a small amount of refrigerant – 14-28 ounces (397,794 grams), so if you lower the level of refrigerant, you should not add too much.

AIR CONDITIONER MALFUNCTION: Malfunction

If the air conditioning system drives cold air, then hot, maybe it freezes. This may be due to the presence of air and moisture in the system, resulting in ice formation and blocking the throttle tube.

Excess air and moisture are pumped out of the system using a vacuum pump that can create and maintain high vacuum (29 inches) for at least 30-45 minutes.

For best system performance, the air content in it should not exceed 2%. With each percentage by which the air volume in the system increases, a corresponding drop in cooling capacity by about one degree occurs. An increase in air volume of up to 6% can cause a significant decrease in cooling capacity and freezing of the evaporator.

The cause of air penetration into the system may be leaks, refueling the system without first evacuating and / or refueling the system with a mixed air mixture. Air can be sucked into the recirculation tank if air conditioning is present or if there is a leak. Therefore, the refrigerant recovery tank must be checked and cleaned daily. In some cars this is done automatically, but if the equipment does not have an automatic pump-down cycle, the pressure and temperature in the tank must be measured and compared with the static pressure reference table.

Some refrigerant identifiers may detect air in the system as well as other unwanted impurities. The identifier must be used to check the refrigerant before servicing the system in order to avoid cross-contamination of the recirculation and recovery equipment..

Possible causes of interruptions in the operation of an automated air conditioning system due to electrical problems:

• Faulty low pressure switch. This relay prevents the compressor from starting when the refrigerant level is low..

• Faulty compressor clutch. To drive the compressor electromagnetic clutch, the maximum battery voltage is required. With a low voltage or too high resistance of the coupling winding, the air gap is too large for the coupling to move the compressor.

• Faulty compressor clutch relay. Check if the relay is receiving power when the air conditioner is on. Also check relay wires and ground connections. If the air conditioner starts to work when connecting the bypass wire bypassing the relay or when directing the battery voltage directly to the compressor clutch, then most likely the relay is damaged.

• Faulty air conditioning control switch. The switch may be worn out and cannot provide good contact when turned on..

Some possible causes of interruptions in the operation of an automated air conditioning system, in addition to all of the above, include the following:

Faulty control unit (in this case, you will probably need a dealer auto scanner to read error codes and perform self-diagnostics).

Faulty temperature sensor (outdoor temperature sensor, interior air temperature sensor, evaporator temperature sensor or sunlight sensor). A factory scanner is required to diagnose the system..

AIR CONDITIONER MALFUNCTION: NOISE

The noise from the compressor usually means that the compressor is living out its last days. However, noise can also result from contamination of the refrigerant (operating pressure too high), the presence of air in the system, or the use of the wrong type of grease.

Noise can also be caused by the contact of the hoses with other components in the engine compartment. Check the route of the hoses, the location of the support brackets, etc., to determine the exact source of the noise.

Nasty odor from the air conditioning system

If the air conditioner blows out air that smells like an old sports shoe, this indicates that germs appear on the evaporator. Mold usually forms in dark, damp places. Bacteria can also breed in such conditions. Such air can also be harmful to health (have you heard of the “Legionnaires’ disease”?).

To get rid of unwanted organisms, various chemicals are sprayed directly onto the evaporator or through blowing boxes or air intakes. Many replacement evaporators are chemically coated to prevent mold and bacteria. Drainage pipes that drain condensate from the evaporator must also be inspected and cleaned..

RINSING THE AIR CONDITIONING SYSTEM

If the compressor fails or precipitation and dirt accumulate in the system, the condenser, evaporator and hoses must be flushed with an approved chemical (e.g. Dura 141b). Flushing – eliminating all sediment and metal wear particles – will help prevent further compressor failures and clogging of the system. You can also get rid of contamination by replacing heavily soiled parts, such as a condenser, battery or receiver-drier, orifice tube or expansion valve, but flushing will be a more practical and economical solution. But in any case, the throttle tube or expansion valve must be replaced.

NOTE: Some types of compressors are very difficult to flush completely. These are capacitors with a parallel flow of steam and water, as well as capacitors with very small channels. In the event of contamination, such capacitors should be replaced to reduce the risk of repeated failure. For safety reasons, it is also recommended to install a pass filter.

When the compressor fails, a large number of metal wear particles get into the system. Most of these particles accumulate in the condenser and can form blockages, leading to a decrease in cooling capacity. If this debris enters the fluid line through a condenser, it may plug the throttle tube or expansion valve. This can result in blocking the flow of refrigerant and lubricating oil, which can cause the cooling to stop and even damage the compressor. Metal particles can also move back from the compressor through the suction hose, resulting in clogging in the battery or receiver-dryer.

Another source of problems may be wear particles from old hoses that break apart from the inside. Small pieces of rubber may form a blockage in the throttle tube or expansion valve..

Precipitation is usually the result of moisture in the system. The resulting blackish mucus can damage the compressor and clog the throttle tube or expansion valve. The moisture-absorbing substance in the battery or receiver-dryer is designed to prevent such a development of events, but this substance can absorb only a small amount of moisture. When it is completely saturated with moisture, a precipitate begins to form. Therefore, if there is contamination, leakage in the system or it must be open for repair work, replace the battery or receiver-dryer.

Flushing the system is also necessary to remove residual lubricating oil. This must be done when changing from R-12 to R-134a, and also if the lubricating oil is dirty or the system is filled with the wrong type of oil. Flushing out old oil will help prevent oil overflow, lower cooling capacity and / or lubricant incompatibility problems..

For safety reasons, after washing, you can install a high pressure filter to protect the throttle tube or expansion valve from residual wear particles and / or a second filter in the suction hose to protect the compressor.

TRANSITION TO R134A

As long as R-12 refrigerant remains available, there is no need to convert old cars to R134a, since R-12 refrigerant-based systems do the best job of cooling when charged with R-12. However, switching to R-134a really makes sense if the air conditioner needs major repairs (for example, replacing a compressor, condenser or evaporator). The additional cost of switching to R134a does not really affect the cost of repairs.

The basic procedure for transferring a system to R134a can be performed in two ways. The first method recommended by manufacturers, as a rule, implies the following algorithm of actions: remove old mineral oil from the system; install a new battery or receiver dryer containing a desiccant (X-7) compatible with R134a refrigerant; replace o-rings (if necessary); install or replace a high pressure switch and / or throttle tube (if necessary); then add special polyalkylene glycol oil (PAG) or charge the system with R134a refrigerant.

According to the technical specifications, it is necessary to install fittings designed for R134a on the service openings of high and low pressure in order to reduce the likelihood of cross-contamination of the refrigerant during the next vehicle maintenance, as well as provide the vehicle with a mark confirming the transition to R134a.

The second way is fast and cheap. In many older cars manufactured from 1989 to 1993, in order to convert an air conditioning system designed for R-12 refrigerant to a R-134a refrigerant system, you can simply pump out R-12 residues (Note: refrigerant cannot be released into the atmosphere – it’s illegal!), Add polyester oil (POE), which is compatible with both types of refrigerants, and then charge the system with R-134a refrigerant.

NOTE: The second method may not apply to some cars if their compressors are not compatible with R-134a (compressors with a Viton seal will have to be replaced). We are talking about such original compressors as the Tecumseh HR980, some Keihin models, as well as Panasonic compressors with a spool valve in old Nissan cars.

Due to the fact that the R-134a refrigerant increases the pressure at the compressor outlet and the allowable load on the compressor, some lightweight compressors may not be strong enough to operate on the R-134a for a relatively long period of time. This applies to Harrison DA6 and Ford FX-15 compressors. The Harrison DA6 compressor can be replaced with the HD-6, HR-6, or HR-6HE. Ford FX-15 compressor can be replaced with FS-10 compressor.

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