QuestionMY 2003 JEEP GRAND CHEROKEE BLOWS COLD AIR ,BUT ONLY OUT OF THE DEFROST. NOT OUT OF THE VENTS. WHAT IS THE MOST COST EFFICIENT WAY TO REPAIR THIS? THANX.......
AnswerRoman,
The most cost efficient way to repair anything is to do the labor yourself. Providing that you have a little bit of mechanical knowledge, and a couple tools to include a handheld vaccuum pump and multimeter, you should be able to do this ok. It may end up being somewhat lengthy in order to get to the faulty part, dependant on what you find, sometimes this involves removing a good bit of the dash.
OK, now I am going under the assumption that you are talking about a Grand Cherokee Laredo with the manual A/C system. If you have a different version of this vehicle or the automatic A/C system, it may vary a little, but the majority should be the same.
Your door actuators are operated on a vaccuum system. Dpendent upon where you set the control head, this sends an electronic signal to a vaccuum harness module. This signal tells individual valves within the harness connector to either open or close a particular port and allow either a vaccuum to be pulled or allos the port to vent. This valve in the connector is connected to different actuators opening or closing the particular doors needed. Looking at your vaccuum diagram, in order for all of the air to be directed to the defrost vents, all of the lines are vented right now. No vaccuum is being pulled on any of the lines. That leads me to 3 possible conclusions.
1. Your vaccuum source. Perhaps it has become disconnected from the vaccuum harness connector, it has developed a leak that does not allow enough vaccuum to be pulled on any line, or there is a problem with your vaccuum source, and it is not providing a vaccuum in the first place. Easiest way to check this... locate your vaccuum connector harness. It will look somewhat like a wiring harness connector, but larger. It will have 6 vaccuum lines attached to it. The colors are... Red, Blue Green, Yellow, Brown, and black. The black line is your vaccuum source input line. Disconnect it and put your finger over the opening. Does it try to pull in a bit of your skin? If so... the source vaccuum is good. If not, then it is not receiving the vaccuum to this line in the first place. This gets its source from your vaccuum reservoir located behind your right headlight assembly. You will have to remove the headlight assembly to check as to whether the black line is connected to the reservoir valve itself.
2. Your vaccuum harness connector is faulty. If it is receiving the right signal from your control head, and refusing to switch the valves in the lines, it would cause your description of your fault. There really is no easy way to check this from a typical home garage, other than process of elimination. You can ensure that your door actuators are working properly by using your handheld vaccuum pump. If you pull a vaccuum on the individual lines, you should see some difference as to where the air flow begins coming from. If you need the complete diagram broke down, let me know, and I will work you through each mode and which lines are vented and vaccuumed.
3. Your control switch in the control head may not be sending the signals necessary for the vaccuum control harness to switch the routings. This is the most common fault, when it comes to a vehicle as new as yours. If it was an older vehicle then I would head to the vaccuum lines leaking. To have this checked, I would recommend you take it to a reputable shop and have them do it. They have the proper diagnostic equipment to do it correctly.
If I was working on the replace parts to find the fix method, I would start with the head unit. This is typically an easy replacement and returnable if it doesn't get beat up inthe event it doesnt fix your problem. It also is relatively cheap. GENERALLY. You have to keep in mind that you are working with a jeep. Through my experiences, Jeep parts are often up there in price with the BMWs and Benz' But I would expect about 100-150 dollars for the control head.
I hope that this response helps you a bit. If so, please remember to rate this answer. Thank you for the question and good luck in everything. If I can do anything further now or in the future, do not hesitate to ask.
