ok have 05 ford freestar 3.9… the air works perfect until you put on max, then just slows down and sort of drops in temp, on a hot day feels almost humid. any ideas what i have going on here… one guy said change cabin air filter i did and no change.
I have little experience with air conditioning systems, but it sounds to me as though your evaporator core is icing up. When you set the dial to “max”, the blend doors set to recirculate, and the air pushing through the evaporator is cooler since it is coming from inside the car. This may be enough of a temperature difference to allow the evaporator to ice up. I’m not sure what exactly would cause that or even if it’s plausible, so perhaps someone with more experience will drop by and weigh in.
I believe mark has it right.
I like the icing evaporator theory.
On other thing I’d put on the table is the possibility of a switch problem. Some cars don’t have a separate switch for A/C on or off. Rather whether the A/C is on or off is tied to the switch position. (My Ford is like this. I hate it, but that’s how it was designed). On max A/C the compressor should be turned on - but maybe a switch problem is actually leaving it off.
I too belive that mark is right, this is usually caused by a low freeon charge. Have you system check out, but I think you need to be topped off… If you want to do it on the cheap go to walmart or any auto supply store and pick up a can of R134 with a gauge. FOLLOW the directions on the can, and fill the system to its proper level.
I’m not an AC specialist, but I too like the evaporator icing theory.
The flow of the compressed, cooled refrigerant through the evaporator is controlled by either an expansion valve or a cntrolled orafice, depending on the design. I’ve posted a link to give you an idea how the system is constructed.
I really think your best bet is to bring this to an automotive AC specialist (radiator shops often do AC work) and get it diagnosed and fixed by an expert.
thank you all so much, i feel much more informed