Air-Conditioning Diagnosis: Noise and Odors on Your A/C system?

Often diagnosis of an A/C system can be done by observing the operation of the system, including listening for noises. When abnormal noises are heard, they can lead to the problem area.

A typical cabin air filter and housing.

NOISE
Often a customer’s concern is the noise emitted by the A/C system. The following discussion covers the common abnormal noises and their causes.

1. Clutch Noises. The clutch normally makes a clicking noise when it engages and disengages. This noise will become louder as the clutch wears. Once the clutch is severely worn, it will make a squealing noise when it is engaged. This noise can also result from oil on the clutch. A very loud screech or squeal can indicate a seized compressor. A bent drive pulley also can cause a growling or rubbing noise.
2. Hose Noise. The change in pressures in the suction/discharge hoses can set up vibrations that cause sounds to appear from the inside of the vehicle. The noise is typically caused by a hose contacting another hose or part in the engine. Check the routing of the hoses to make sure they are not in contact. Also look for abrasions on the hoses. These can be caused by the contact.
3. Compressor Noise. If the mounts for the compressor are loose or damaged, there will be a rattling or groaning noise. The noise is normally random. At times, loose mounts will also cause premature wear of the drive belt. Worn bearings and/or internal damage to the compressor can cause whining and growling noises when the compressor is engaged.
4. Hissing or Whistling. This is a common and normal noise. When the A/C is turned off, a high-pitched whistle may be heard. This sound is caused by the pressures that are equalizing in the system. The high pressure moves to the lowpressure side through the metering device. This movement can result in a whistle or hiss.

ODORS

A somewhat common concern of customers is a smell emitting from the A/C system. This moldy and musty smell is due to a buildup of moisture on the evaporator or the cabin filter. Moisture buildup is caused by the evaporator doing its job. As the temperature inside the vehicle is lowered, moisture is separated from the air; the moisture should be able to drain but sometimes the drain is plugged or dislocated. When a customer complains about the smell, check the evaporator drain. Also, the cabin air filter needs to be periodically changed; if it has not been changed, there will be odors that offend the passengers. Products are available to disinfect the evaporator and ductwork. These kill any odor-causing bacteria. Application of these products may require access to the evaporator, requiring disassembly of the HVAC system.

Many Toyotas have an ion generator called the Plasmacluster generator that improves interior air quality.

Cabin Filters. Cabin air filters are designed to capture soot, dirt, pollen, and other pollutants that enter a vehicle through its heating, A/C, and defrost systems. Today more than 80 percent of all new vehicles sold in the United States have a cabin air filter or a slot where one can be installed. Cabin air filters are typically located behind the glove compartment, under the dash, and under the hood. Some cars have the filter in the HVAC case between the blower motor and evaporator core. A cabin filter is a critical part of the HVAC system. If the filter becomes dirty or clogged, less air will be able to pass through the filter. This will adversely affect the operation of the HVAC system.

Many Toyotas have an ion generator called the Plasmacluster generator ( Figure 55–9 ) that improves interior air quality. It uses a high-voltage device that emits a slight sound. With these systems, dust will accumulate at the driver-side air vent.

Clean it with a cloth; never spray solvent into the air vent. Replacement of the filters is part of a vehicle’s PM program; normally a filter should be replaced every 12,000 to 15,000 miles (19,300 to 24,140 km) or at least once a year. This interval really depends on where the vehicle is typically driven. The procedure for replacing the filters varies with make and model; always check with the manufacturer.

There are two basic types of cabin air filters: particle-trapping and one that has an additional charcoal layer for odor absorption. Some particulate filters have a section that traps larger particles and another that is electrostatically charged to attract and hold smaller particles.

A charcoal type will hold a lot of odorant, and under some conditions it may release trapped odors. This is why these filters should be replaced on a regular basis. There are two alternatives to the charcoal filter: a filter element impregnated with baking soda and a filter with a biocidal cartridge. Both prevent the growth of bacteria, mold, mildew, algae, and yeast.

Some vehicles are also equipped with an air quality sensor in the main inlet duct of the HVAC system or in front of the condenser. The sensor detects the presence of undesirable gases in the incoming air, specifically carbon monoxide and nitrogen dioxide. Within seconds of detection, the ventilation system closes the outside air inlet and recirculates the air until the pollutants are no longer at an unacceptable level.