Problem with rear A/C controls - aware of relay issue.

I have experienced the rear fan running on after the engine is shut off issue and have ordered the two replacement relays mentioned in other threads.

But, I'm having a different problem with my rear A/C heat controls and am looking for some tech advice.

When the rear control is active, the fan control doesn't work at all. Adjusting the fan speed has no effect and setting it to off does nothing - the fan keeps running. The air flow will change if I adjust the temp control and the fan will slow down if I set the temp control anywhere around the middle position to full hot. It doesn't matter if the main control is set to auto or manual. Only the temperature control appears to have any effect.

The front controls appear to be working fine as far as I can tell from running the front A/C and heat through the various modes. I can feel air under both seats when I have the control set to floor. But the front controls don't seem to have any control over the rear unit in the way the manual shows. The air comes from the lower vent at a single speed and that's it, regardless of how the main controls are set.

I'm thinking I have a bad rear control head or could this be caused by the bad relays?

Start with replacing BOTH front and rear a/c relays and then update the post at that point. My bet would be put on the relays.

I received the new relays today and installed them.

There was some change in operation. Now, the front control panel seems to have control over the rear console vent's direction of air flow. But varying the fan speed on the front control doesn't regulate the rear fan speed - it runs at just one speed. The rear fan control still does nothing when the rear control is active. It won't shut the rear fan off and it has no effect on fan speed at all. The only time the fan slows down is if I adjust the temperature control from mid point to full hot, same as before.

So, I'm still thinking that I have a bad rear control head. But, I'm going to let the dealer figure that out. I have a MEPP agreement on the vehicle and this should be covered less the deductible.

The relays weren't a waste of money, they definitely did solve part of the problem.

Very strange. Yes it sounds like the fan speed control knob may be to blame in the rear...but this is very strange because usually that knob is hardly ever used, so you would think it would last to infinity and beyond.

Hey it's a part and parts can fail. Sounds like youre past your warranty though. What year CX 9?

I know all about failed parts (on my vw's) motor mounts, a/c, valve cover gasket, head gasket, piston rings, water neck, water pump, alternator, starter, compressor, thermostat, window regulator, cat converter, just to name a few. Had to ditch VW (B4 Passat GLX and MKII Jetta GLi) It was like a house payment just keeping them on the road.
The CX-9 is off to a good start so far, comparatively.

My 9 is a 2007. I did some reliability data mining and both the 07 and 08 have a history of A/C rear control failures along with the relay problem.

For all I know it might have gotten whacked when I had the 9 in for a recall to modify the power points in the console and rear area to prevent a blown fuse and false airbag warning light. I have the factory manual and am going to run the diagnostics on the system and see if there are any failure codes present. I'll also run the function test cycle and see how everything works.

Thanks for the input!

[edit]

I put the AC controls into diagnostic mode and there was a code 74 displayed - failure of communication between the front control and the rear fan switch which is consistent with what was happening. I then ran the test cycle routine to check the system function and it fully passed testing. Everything worked the way it was supposed including the front and rear fans running in perfect sync to each other. At that point I concluded the rear control was the problem. I removed the switch assembly from the console and popped off the fan control knob to check it out. Out falls this little electronic rheostat that's supposed to be soldered to the circuit board. There was the problem. So, I got out the soldering iron and made a temporary repair by re-soldering the 4 connections back to the circuit board. All is working perfectly now.

I don't know what happened for sure, but somehow that little component got broken loose from the circuit board. I will say that although the control looks sturdy from the outside it's pretty fragile inside. I don't think it would take much of a whack on the knob to break that rheostat circuit off the board.

Anyway, mystery solved and a temporary fix applied. I'm going to order a new control because my fix won't last forever.

[edit 2]

Received the replacement switch assembly on Friday and replace the original one I had repaired. There's a definite difference in the feel of the new switch. The original had a smooth, infinite sweep to both controls with no clicks. The new switch has distinct clicks you can feel as it's rotated. It seems to have a more solid feel to the controls too. If I'm reading the part number correctly, the switch I received is the 6th engineering revision of the control. They must have had a fair number of problems with them to have had that many changes.

Hey, I am having this same problem, can you tell me what the part number was that you ordered? Also are you saying it was the front console control panel, or the panel for the back (the one on the back of the center console)? Thanks.

Rear control was the problem. PN TD11-61-325E. Shop around for it to get the best price. It can get spendy if you aren't careful about where you buy it.

Also replaced the HVAC system relays under the hood. PN G115-67-730. 2 are required.

Ill give that part number a try, already replaced the relays a few years ago.

Dealer replaced (at no cost to me - still under warranty) both relays and the rear blower component causing the problem with "run-on" after vehicle was shut off. No problems since then.

I have a 2007 CX9 with the rear blower "run-on" after shut off. Last week the fan stopped working completely. Could the blower motor relays be causing this problem also?

I replaced the relays last night and the fan came back to life. Seems to work fine again.

I am having similar problems. Replaced the relays which seemingly fixed the issue with it coming on after shut-off. However, the fan speed issue is still there. It's on full blast whether it's off, on, high, low. Is the only solution to but a new $250 control assembly?

Hi jb1239,

I'm having the same problem with my 2007 CX-9 rear air vents, mine don't blow at all. Could you tell me what yo uneeded to do to fix yours?

Tom