Freon consists of a pressurized gas and lubricant used to provide cooled air to a vehicle passenger cabin. Most vehicles today, and all with a production date post-1994, use R-134a refrigerant -- some manufacturers switched to R-134a as early as 1992. R-12 refrigerant was used in most vehicles with a production date of 1994 or earlier and has been phased out of production, though recycled R-12 is available to licensed professionals. The basic components of an automotive air-conditioning system includes the compressor, evaporator, expansion valve, condenser and accumulator, along with hoses and fittings. When the air-conditioning system has lost all refrigerant, sometimes incorrectly referred to as "Freon," there are a number of symptoms to look for.
Refrigerant Loss While Driving
If you notice a sudden loss of cooling temperature in the air-conditioning vents during normal driving, chances are the compressor or clutch has stopped, or your system has experienced a catastrophic hose or seal leak. The sudden burst of a high-pressure line at the fitting or hose will cause a white, steamy-like cloud to eject from the damaged area, sometimes accompanied by a hiss or a rattling sound coming from the compressor. Although sudden refrigerant loss during driving happens infrequently, it is still one of the most obvious signs that pressurized refrigerant has blown from a damaged hose, fitting or seal.
Clutch Function and Protective Switches
With the car running and the air-conditioning switch turned to high, for the fan setting, and the temperature control set for the coolest mode, the air-conditioning compressor clutch should activate and engage the compressor. If the clutch does not come on, and the air-conditioning relay and fuse are good, it could indicate that the low-pressure switch has activated, disconnecting the circuit between the clutch and the compressor. The low-pressure switch acts as a safety device, or backup relay, disallowing the compressor to run when low or no refrigerant exists. To verify that your vehicle has a lower-pressure switch, read your owner's repair manual, which will identify it.
Visual Refrigerant Leaks
The air-conditioning system should be checked for visible refrigerant leaks if a total evacuation of refrigerant is suspected. Refrigerant contains an oily lubricant that shows up as a film, splatter or liquid stream on a damaged component. Areas to inspect include the front shaft seal of the compressor, the high- and low-pressure lines, the fittings connected to the compressor, service ports, condenser, evaporator and accumulator. The condenser, which resembles a small radiator, should be checked for cracked fin tubes and seams. The discharge residue of refrigerant from a slow leak will often be covered with patches of dark-colored dust, easily discerned from the cleaner areas.
If the clutch activates when the air-conditioning unit is turned on but will not engage and rotate compressor, it indicates frozen or jammed compressor components. If no refrigerant exists in the system, it robs the compressor piston, valves and bearings of needed lubricant. This worst-case scenario can happen while the engine runs and sometimes be accompanied by a loud rattling noise, clunk or metal-to-metal screech. A slow leak, which eventually leads to total refrigerant loss, will begin by causing unusual compressor noises that worsen as the refrigerant escapes.
Air-Conditioning Gauge Readings
The air-conditioning system pressure can be measured by hooking up an air-conditioning manifold gauge to the high- and low-service ports. The high-side (red) gauge hose connects to the high-side service port with a quick-release fitting, while the low-side (blue) gauge hose connects to the low-side service port. With the engine and air conditioning off, and by opening the blue and red gauge knobs, the static pressure on the gauges should read 80 to 105 psi. With the air conditioning turned on to maximum and the engine running, the low-side gauge should read 25 to 35 psi, while the high side should read 200 to 350 psi. Substantially lower or near 0 readings indicate total refrigerant loss.
Some vehicles are equipped with a sight glass that provides a visual inspection of refrigerant movement through the liquid side, or high-pressure line. A fully charged system will show a rush of clear fluid moving through the line, while a low refrigerant level will show bubbles or a foggy appearance. A lack of any refrigerant movement, clear or otherwise, will indicate no refrigerant present in the system.
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