Saturday, January 12, 2013
Working of and Problems with Car Air-conditioner -- Part 2
Let us now look at some of the common complaints about car air-conditioners.
(a) No cooling: When the air-con is switched on and warm air comes out, a highly probable cause is low or no refrigerant in the system. The refrigerant may have escaped from a leak in any of the components of the system. Some air-conditioning systems use compressors that have no oil sump or internal reservoir, depending on oil circulating with the refrigerant for lubrication. In such systems, there is a low-pressure safety switch that prevents the car's engine from engaging the compressor if the system pressure falls too low. This prevents possible damage to the compressor caused by insufficient lubrication.
A technician will always check whether the compressor is working when the air-con is turned on. If the compressor's magnetic clutch is not engaging, a fuse may be blown or the wiring is faulty. Replacing the blown fuse is a temporary measure as the root cause of it blowing earlier needs to be rectified to prevent the same thing from happening again. If the magnetic clutch is receiving voltage but is unable to engage the compressor, the clutch is defective and needs to be replaced. If there are signs of leakage around the compressor shaft seal, it will also have to be replaced. Sometimes the clutch engages the compressor but the latter refuses to turn, resulting in the belt squealing. In this case, the clutch is defective and a new one needed.
A compressor normally fails because of loss of lubrication from one of the following causes: insufficient refrigerant in the system due to leaks; a blockage in one of the tubes leading to the compressor; wrong service procedure such as not topping up oil when it is lost through component replacement; or using the wrong type of lubricant. Mineral oil is used in R-12 systems while PAG oil or POE oil of various viscocities is used in R-134a systems.
A condenser-cooling fan that is not working may also cause the air-conditioner to blow hot air. This fan should come on and remain on when the air-conditioner is switched on. If the fan's motor, motor relay or wiring is defective, the fan may not work.
After inspecting the compressor to trouble shoot a no-cooling problem, the technician will check the system pressure. To do this, a pair of gauges is fitted to the high and low service fittings of the system. If the readings of both gauges are low, the system is low on refrigerant and needs topping up. Before recharging, be sure to check for possible leaks.
Actually, all air-conditioning systems leak through microscopic pores in the hoses and past the rubber seals but such leaks are minimal. There are a few methods to trace the location of leaks. The simplest is to spray soapy form. Another easy way is to inspect whether there are any oil stains around hose connections, compressor clutch and other fittings. When a refrigerant leaks, it evaporates into thin air leaving no trace except for the compressor oil reside that leaks along with it. To detect leaks, your technician may use an electronic leak detector that reacts to the presence of refrigerant in the air. Sometimes a fluorescent dye is introduced into the system, and an ultraviolet light is used to spot any dye leaking out with the refrigerant.
A leak, no matter how small, should be fixed as soon as possible. A leak allows air and moisture lo enter the air-conditioning system, which can react with the refrigerant to form corrosive acids and sludge. These substances can damage the compressor, block orifice tubes and eat pin-holes in the evaporator and condenser. Another important reason for fixing leaks is that R-12 is ozone depleting and R-134a, though ozone-safe, contributes to the greenhouse effect.
(b) Intermittent cooling: The car air-conditioner may blow cold air for a while, then followed by hot air. When this happens, the system is already contaminated with air and moisture. Air can reduce the effect of the refrigerant, while moisture can freeze, forming ice and causing tubes and valves to be blocked. Apart from getting into the system through leaks, air can be introduced into the system bynot evacuating it before recharging it with air.
(c) Noise problem: Noise from the compressor means it is going to kaput. Using the wrong type of compressor oil, too much pressure in the system, or loose parts rattling against other components in the system can also cause noise.
(d) Odour problem: If the air-conditioner emits cold air smelling like sweat-stained socks, mould has already grown on the evaporator. The presence of mould attracts bacteria that can make the air unhealthy to breathe. To get rid of the mould, spray chemicals on the evaporator or through the air intake.
In servicing the car air-conditioner, the technician may find it necessary to flush its parts. Don't think he is deliberately doing unnecessary flushing to bill you higher! When a compressor fails, a lot of metallic debris is introduced into the system. It often collects in the condenser, reducing the ing the cooling performance of the refrigerant. Worse, the debris may pass beyond the condenser and enter the liquid line, blocking the flow of refrigerant and lubricating oil.
Old tubes are another potential source of trouble. Rubber flakes may peel off and be carried along the orifice tube, causing a blockage. As pointed out earlier, moisture contamination can cause sludge to form. If your car air-conditioner is more than five years old, the desiccant in the accumulator or drier has probably become saturated. As it can't remove any moisture, sludge begins to form. For more protection, after flushing, ask the technician to install a filter to protect the orifice tube from any residue debris that may be left in the system and/or a second filter in the suction hose to protect the compressor.