Signs & Symptoms of a Clogged Automotive Air Conditioning System

by Chris Stevenson
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The automotive air conditioning system consists of several components, including a compressor, evaporator, condenser, expansion valve, orifice and receiver-drier. Any one of the components can fail, or several can be affected by the same problem, such as leaks or blockages. Blockages in the air condition system cause certain signs and symptoms. Certain components will display peculiar behavior or erratic function, which can be observed by the vehicle owner.

Compressor Noise

Compressor noise can result from internal component wear and manifest itself by a rattling, grumbling or howling noises that comes from the compressor unit. This happens when contaminants or air enters the system but almost always points to the lubricant breakdown. When the Freon oil breaks down, it causes friction that flakes off bits of metal. The metal travels through the hard line and into the condenser, causing a blockage. With a heavy accumulation, the metal debris can travel further and block the expansion or orifice tube.

Auto Shutoff

You may notice the compressor cycling on and off, causing a repeated clunking sound. This could be attributed to an automatic safety shutoff feature that detects lower than normal pressure in the system. The auto shutoff will turn off the magnetic clutch to the compressor if it reaches a dangerously low system pressure. Low system pressure will be caused by air, sludge or contaminants in the lines, condenser, expansion valve, evaporator or orifice tube.

Compressor Freeze

You can visually look and listen to see if the magnetic clutch engages to run the compressor by having an assistant turn the AC controls on to maximum while you watch the clutch from the engine compartment. A compressor freeze means that a lack of Freon lubricant or dirty lubricant has jammed the compressor. You can manually try to turn the outside of the clutch to see if it rotates.

Intermittent Cooling

Watch for signs of intermittent cooling that causes the flow of warm air, cold air and cool air from the vents. This symptom usually points to a freezing up of the air conditioning system. When moisture and air combine, they can form ice that can block the orifice tube. The normal air conditioning system has less than 2 percent air by volume. If more air enters the system, it displaces the working freon. Depending upon the outside temperature, the cooling capability can be very erratic.

Gauge Diagnosis

With an AC gauge hooked up to the low and high side of the manifold lines, a pressure reading can evaluate the condition of the system. With the engine and AC off, a normal reading for an 80-degree day should indicate 56 pounds per square inch on the low side gauge or 70 psi on a 90-degree day. If the low and high side gauge readings show below normal with the AC on and engine running, a restriction exists in the orifice tube, expansion valve, compressor or high side pressure lines

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