ac fan switch problems

I have a 99 passport w/ac that has worked fine for the 2 years I've had it. Now when I move the fan switch from off to 1, 2, or 3 I have no problems. Blue "ac" light is on and car is blowing cold. When I switch to position 4 on the fan selector, the fan kicks up a notch like it should, but the blue light goes out and the air that comes out isn't nearly as cold as with any other fan switch position. any ideas?

i can't live in AZ without my ac's "4th gear" blowing cold. any ideas at all?

That is really weird, 'cause the blower speeds and a/c switch are totally seperate. The only thing I can figure is, on speed 4, so many amps are being drawn that the a/c is tripping off (relay cant hold-in). The blower motor is a HIGH electrical draw item. A (new) higher capacity battery or maybe a new alternator *could* be the fix. I'd start by swapping relays around just to rule that out.
G/luck
Joel

thanx for the idea '02. My battery is old and I was going to replace it before this summer anyway. I also have a 500w fosgate amp and aftermarket fog lights that are always running as well, drawing extra electricity. so all that may be contributing to my issue.

I have the exact same situation with my 99' rodeo. Everything works great in speeds 1,2,3 but no go with 4. The A/C compressor shuts down. It will come back on if I put the fan switch back to 3. I do have a new battery so that rules that our for me.

99zhfkaf - Did you get yours fixed?

Thanks,
Troy