PAJeepGuy2004

I have a 2004 Jeep Grand Cherokee Special Edition model. Recently my damper control selector switch/**** that controls the heat/AC air flow direction (i.e. dash, recirc, defroster, etc) has stopped working. When turning the control **** to any position the air flow only comes out at the vents in the defroster position.

Hoping that someone can please tell me what is possible failure and how to repair. Before I remove the dash to investigate the blower dampers, I wanted to be sure that it wasn't a failure on A/C & Heater Climate Control (part 55115904).

Thanks for your answer

dave1123

Welcome to CF!

That function is known as the "mode selector" and is vacuum controlled. Look for a leak in the vacuum source, usually the "T" fitting on the firewall of the engine compartment. It comes off the intake manifold and goes to the heater control, the cruise control actuator, and the vacuum reservoir. You probably won't see the reservoir because it's under the right front headlight and the supply hose disappears underneath the battery. There is also a check valve on or near the manifold to hold vacuum when you shut off the engine. It could also be the valve in the heater control console itself. The "hose" is a hard plastic tubing.

PAJeepGuy2004

Dave,

I will check my vacuum hoses and hopefully find where the leak is located. If no leak is found, then it's likely that the reservoir or check valve have gone bad. I'm glad to know that I don't have to remove the dash for this repair.

Thank you for your help!

dave1123

You MAY have to remove the heater control from the dash, but that's easy to do. Check wjjeeps.com for that procedure. A lot of the cover panels on the dash are just mounted with spring clips and the heater, radio, etc are just phillips screws. BTW, I had to replace some dash lighting bulbs in my instrument cluster and I freaked out about it! WJjeeps showed me it's just one spring mounted panel and 4 phillips screws! Couldn't be easier. If yours have the white gauges, they are electroluminesent. No bulbs.

The mode switch has a large rubber plug on the back with plastic tubes coming out of it. You can check your vacuum supply there with the engine running. All the reservoir does is hold vacuum to close the heater doors when you shut off the engine. It also smooths out the vacuum pulses and makes for a more constant supply.

Just to show you how important a reservoir is, my first car was a 1937 Dodge which had vacuum windshield wipers. When you hit the gas, the wipers would stop! I took an empty Hawaiian Punch can and soldered a brass pipe into one end for a hose. It worked perfectly! Later models had a vacuum boost pump as part of the fuel pump, but a reservoir still helped.

Sorry this post is so long. Can you tell I'm bored?

PAJeepGuy2004

Dave,

Thanks for the additional information regarding removing the heater control. Actually I have been replacing some of the bulbs on the instrument cluster and the bulbs behind the AC button and the seat heater control switch. A very easy task!

Didn't have time today, but will be tracing out the vacuum lines tomorrow, hoping to find the leak. I may have to replace the entire vacuum line assembly to ensure all check valves are functional. Thanks for the tip on checking for leaks at the rubber plug located behind the mode selector. Good place to begin.

Btw, the juice can was a innovative idea. Sometimes we have to improvise when the required part is not available.

Thanks again

PAJeepGuy2004

Dave,

Your advice that a vacuum line was most likely my problem with AC/Heater air flow and cruise control was perfect. I found one vacuum line going to the intake manifold barely attached. After reconnecting all is working great again! You saved me over $600! Thank you very much!

dave1123

Diagnosing mechanical stuff like that is easy. It gets difficult when it comes to electronics, especially low voltage analog circuits, like sensors. Voltage levels are critical because most of them operate on 5 volts with their outputs at millivolts. What really makes me cringe is when I see 02 sensors with twisted pigtail connections!