Air Conditioning problem
2001 Ford Taurus 6 cyl Front Wheel Drive Automatic 152800 miles
In 2007, I had a local shop replace my A/C compressor and clutch. Ever since then, I have been experiening problems with my A/C system. It operates well during operations in which the rpms are constantly changing, however, after 30-45 minutes of freeway driving or idling, when rpms are constant, the a/c system will act as if it is blocked. The blower is operational and air is trying to move through the air vents. There is a clear sound of something blocking and it is coming from the dashbord on the passenger side. I've disassembled the blower motor and fan inside the dash and it works finde and checked the vent door inside the dashboard and it appears to function as it should
I've taken to the shop several times only to hear they cannot find a problem. I've had them test the vaccum system and no leaks were detected. This happens on all settings, A/C, vent and defroster. The only thing that temporarily solves the problem is to turn the entire system off for a period of time, usually 15 minutes or so before it will work again. I am not sure it this is normal, but the A/C lines inside the engine compartment will be covered in ice when I am experiencing this problem. I read somewhere on the internet that another Ford had a similar problem and I believe the solution in that case was either the high pressure or low pressure sensor needed replacement. Its driving me nuts because its starting to get hot and I want to fix my A/C know what to change or direct the shop to change.
Your problem is definitely related to the evaporator icing up and blocking the air flow. This is caused by the compressor not cycling as it should, and allowing the system to get too cold. The low pressure switch should cut out at about 25 psi, and cut in at about 45 psi. When the low side pressure goes below 25, it allows the system to cool to a point of forming ice from the humidity in the air. The high pressure switch is to prevent excessive loading on the compressor, engine, and hoses - if the pressure gets too high, it can cause a hose or compressor failure, and can overtax the engine causing overheating or loss of power.
An undercharged system can also cause icing, but normally, the low pressure switch will prevent icing.
My first suggestion is to check the system with gauges. Check the low pressure cutout switch for proper operation. Also check to make sure that the compressor cycles as it should. Could also be that the compressor clutch is not releasing.
Also check the air temp at the center dash outlets with an accurate thermometer. If the temperature is falling below 32 degrees F. It is too cold.
My feeling is that your low pressure switch is the most likely cause of the problem, but I always recommend doing some diagnostic work before you start throwing parts at the problem.