My a/c seems to be stuck in defrost mode. No matter which setting I turn the dial to, the air only blows out of defrost vents. The a/c does work, the air coming out is very cold, I just can't get it to come out of any other vents. Help! I don't even know where to begin.

Thanks! Jennifer

My a/c seems to be stuck in defrost mode. No matter which setting I turn the dial to, the air only blows out of defrost vents. The a/c does work, the air coming out is very cold, I just can't get it to come out of any other vents. Help! I don't even know where to begin.

Thanks! Jennifer

Check the vacuum hoses coming from the blower going into the dash. There should be two hoses: One for the forward vents and another for the defrost and floor vents. The hose for the forward vents themselves may have come out and thats why you only have air coming out of the defrost vents. I made this mistake before when i replaced the blower on an older car I had forgotten to plug the vacuum hose back in. So try that first and see what happens.

Sean,

Thanks so much for your quick reply! How do I check those hoses? What do I have to remove to find them?

Jennifer

Does the 01 not have electrically motivated mode doors? Do you have a digital temp readout on the AC controller (ATC)? If so, you can pull the codes and find out if you have a bad sensor or servo. If it is vacuum controled, likely the issue is under the hood. Look for small (1/4") lines going into the firewall from the engine compartment. Follow those back toward the engine and look for breaks.

Does the 01 not have electrically motivated mode doors?
For the blend/temperature door yes. The mode doors are operated by vacuum, UNLESS it has the Automatic Dual Zone Controls, then it's electrically controlled.

Is the cruise control working? If not, it has lost vacuum and the vent has moved to its default position - defrost. Both use the same vacuum source.

How do I check those hoses? What do I have to remove to find them?
Nothing to remove, just look for a disconnected vacuum hose in the engine compartment - plug it back into the intake manifold nipple. If I recall, on a 4.0L six it's on the drivers side.
The manifold vacuum hose disconnecting is a common occurrence on '99 - '04 Grands.

You all are being so much help and I really appreciate it!

Ok, I took it for a drive and the cruise control does not seem to be working. So that's a vacuum problem, right? What am I looking for in the engine? Will a disconnected hose be really obvious? Because I didn't see anything that looked like it was disconnected.

What else would cause me to lose vacuum? I'm sorry to ask so many questions, I'm really not familiar with all of this, but I don't have the money to put it in the shop, but I'm supposed to be driving to visit family in south Florida next week. (insert smiley for sweating to death here!)

Jennifer

Most of the vacuum lines will be hard plastic lines, with rubber ends. Check for any fittings (tubes) with nothing attached and see if there is anything in the vicinity. Also, follow the lines to see if they are broken anywhere.

For the blend/temperature door yes. The mode doors are operated by vacuum.

Is the cruise control working? If not, it has lost vacuum and the vent has moved to its default position - defrost. Both use the same vacuum source.


Nothing to remove, just look for a disconnected vacuum hose in the engine compartment - plug it back into the intake manifold nipple. If I recall, on a 4.0L six it's on the drivers side.
The manifold vacuum hose disconnecting is a common occurrence on '99 - '04 Grands.
This is exactly the problem I am having. My cruise control stopped working about the same time my vents stopped switching, and I didn't make the connection until reading this... thanks in advance for the help ;)

Just thought I would come back and let you know that, I found the break in the line, fixed it, and my A/C is fully functional again. I haven't tested the cruise control yet, but I feel confident it will once again work. Thanks again. It took me about 3 hours of online searching, but this forum is were I finally found the correct prognosis ;)

You all are being so much help and I really appreciate it!

Ok, I took it for a drive and the cruise control does not seem to be working. So that's a vacuum problem, right? What am I looking for in the engine? Will a disconnected hose be really obvious? Because I didn't see anything that looked like it was disconnected.

What else would cause me to lose vacuum? I'm sorry to ask so many questions, I'm really not familiar with all of this, but I don't have the money to put it in the shop, but I'm supposed to be driving to visit family in south Florida next week. (insert smiley for sweating to death here!)

Jennifer

As it turned out, this was the exact problem I had with my 2000 Jeep Cherokee Sport, and after some serious inspection with no discovery of a problem, I finally followed every vacuum hose from start to finish, and found what looked like a melted line right next to the battery as if some battery acid had dripped on it some how? Maybe start there?

I just cut the mangled piece of line out and found some break bleeder hose I had laying around the garage, and cut off a large enough piece to span the gap. I used some contact cement on the smaller hose ends, inserted the smaller hose ends into the larger hose, waited for the contact cement to dry, and I had a close to no cost fix.