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How to Diagnose Your Car’s AC Problems
1. Is Your AC Cool but Not Cold?
If the air conditioning is set to max cool and fans on high, but is only blowing moderately cool air:
Check to see that the cooling fans on the condenser or radiator are running when the air –conditioning is on.
Look for any restrictions like leaves, bugs or dirt that would keep air from passing over the condenser.
Check the cabin air filter to ensure that it is not clogged.
Beyond this, the next step is to always check the pressures in the system using a manifold gauge set. The recommended high-side and low-side pressures can be found in your vehicle’s repair manual, or online. Once you have your gauges hooked up, move on to observing the AC compressor itself.
2. Start with the AC Compressor
When diagnosing an air conditioning issue, it’s easiest to begin at the compressor:
With the engine running turn the A/C on max cool, set fans high, and make sure that the clutch is engaging on the compressor. Note: this is not the pulley, but the center piece that engages the pulley to the compressor shaft. If the clutch is engaging and disengaging once every few seconds, this is a sign of low refrigerant. You will also see the low-side pressure on your gauge drop rapidly when the clutch engages, hit a point of too-low pressure, then disengage and the pressure will rise. As you add more refrigerant, the gauge will hold steady, with the compressor running, and should hold at the recommended pressure.
3. Most Problems are Caused by Leaks
Leaks are the most common problem associated with the air conditioning system. If pressure is low, then there may be a leak: Check where the evaporator drains condensation with UV light. Sometimes oil or dye can be seen.
Note: The dye check will not work if the system is too low and the compressor is not cycling.
Still Not Sure? Check These Components
AC Compressor and Clutch
The AC compressor is a rotating pump that circulates refrigerant (Freon) throughout the system.
Common Problems: Leaks in one or more seals or the compressor itself can occur. Particle contamination from worn parts inside the compressor are a frequent culprit. The engagement clutch, called an AC clutch, can also fail rendering the compressor inoperative.
What to Look For: If the refrigerant is low, check for visible system leaks that appear green and oily. Failing internal components caused by normal wear or low AC Oil levels caused by leaks. Failed AC clutch. Failed power supply to the AC clutch caused by a blown fuse, bad pressure control switch, dash control module or a broken circuit wire. Inspect and test before replacing!
AC Accumulator / Drier
The Accumulator/Drier collects and absorbs moisture. Moisture is like poison to the internal system components and can damage the AC Compressor as well. Depending on your vehicle, you may have an accumulator or a receiver/drier.
Common Problems: Internal failure allowing desiccant material to enter the AC system. Like sugar in the gas tank, this stuff in the wrong places can cause major problems. Leaks can result in over-saturation of the desiccant material that can lead to compressor damage.
AC Orifice Tube / Expansion Valve
The AC orifice tube / expansion device filters and regulates the flow of refrigerant through your air conditioning system. Depending on your vehicle, you may have an orifice tube or an expansion valve.
Common Problems: Contamination is the main cause of failure. If the system pressures are too high and/or too low, the expansion device could possibly be the issue. But first, ensure the refrigerant levels are correct and the radiator/A/C Condenser fan(s) are working properly. Remember, inspect and test before replacing!
AC Condenser
The AC condenser looks similar to a radiator and works in conjunction with the radiator fan(s). Air flowing across the AC condenser tubes cool the hot (gaseous) refrigerant that absorbed heat from inside the vehicle. This returns the refrigerant back to a liquid state where it will once again enter the evaporator core and absorb more heat from the interior.
Common Problems: Refrigerant leaks. Contaminant particles from the AC Compressor or AC Accumulator/Drier restricting the flow of refrigerant can lead to poor cooling. While checking the AC Condenser, inspect the Radiator / AC cooling fan motor(s).
AC Evaporator Core
The AC evaporator acts like a huge ice cube with holes in it. It allows the hot, cabin air to flow through the core, rapidly cools this air, and blows it out into the cabin again. The cool air felt from the dash vents is provided by the AC heater blower motor assembly.
Common Problems: The number one cause of failure is a leak due to age and wear. An electronic leak detector is the best way to check for leaks. Give attention to the AC evaporator box water drain tube. Use the tester to search for a leak. A green and oily substance may appear in the drain tube if larger leaks are present.
