Rear a/c not working

[macdven]

Hi all, I’ve got a 2014 D4 and it came with factory rear a/c option.

I recently noticed (only use rear a/c when kids are in the back) that the control cluster in the ceiling that activates the rear a/c no longer illuminates or functions. And yes - I’ve activated the rear option on the front dash

I’ve checked all fuses, and even LR had a look when the serviced the car - though they said they wanted to remove the headlining to haven a more detailed inspection. I opted to try myself to save $$.

I’ve bridged the relevant relay on the dash and tried for power at the rear blower wires. When I did this, if I earthed the blower power (red wire), I got 14v, but using the red/white in the connector, I got a weird (variable/decreasing voltage - <10v).
Am sure the fuses are good and the relay.

I’m not sure if the switching module in the ceiling runs any power or is driven by a canbus, but there doesn’t seem to be any power running to any if those wires that connect into the 3 socket controlling the three round dials. Does anyone know if there is power and which colour wires I could check?

I’ve heard/read that the fuse block may have poor soldering for the rear a/c fuses. Not sure how to check that.

I’d be thrilled to get any guidance … or hear if anyone has fixed a similar problem.

 

[macdven]

BTW, is there a connection behind the A-pillar trim? I think this was removed to fix hail damage. Maybe they hit something??

 

[f1racer328]

BTW, is there a connection behind the A-pillar trim? I think this was removed to fix hail damage. Maybe they hit something??

I think the connection behind there is for the heated windshield but I'm not 100% sure.

 

[macdven]

I think the connection behind there is for the heated windshield but I'm not 100% sure.

Thanks. I'll take it off and have a look.

If anyone else has any other advice as to why the rear a/c may not be working ... I would be most grateful

 

[macdven]

Thanks. I'll take it off and have a look.

If anyone else has any other advice as to why the rear a/c may not be working ... I would be most grateful

I took off the pillar trim and there’s nothing obviously wrong there - all roaring in tact.

Frankly, this issue has me stumped.

I’ve read elsewhere that it could be the fuse block, but feel this would be very unlikely … and imagine it’s also a pain in the ass to fix.

Has anyone had any experience with issues related to faulty fuse boxes?

The next thing I want to test is the switch cluster/module on the roof lining - the actual fan speed and hot/cold controls.

It takes 2 seconds to pop out. Problem is, I don’t have another to test against. If anyone lives near Warrandyte, and has a D4 with working rear a/c option - and you are happy for me to swap the control and test (would take all of 10 minutes) … lemme know. Pulling out the switch is very easy (pull panel down from the front edge facing front of car, and the slide the models forward. Bingo, it’s out.

Mark.

 

[mikem]

Howdy. I noticed a similar issue with my rear AC unit a few weeks ago. I also primarily use the rear AC when my kids are in the back, and I've also noticed that the light is out. Have you managed to resolve your issue? I started troubleshooting my problem based on recommendations from various forums. To make a long story short, I discovered that the relay controlling the rear blower isn't being activated when I press the manual button for the rear AC on the console.

I purchased a relay (RL44) from Auto Zone and took it apart to manually activate the switch - this relay isn't identical to the JLR relay as it lacks a diode. If you want to try this, you can order a relay from the dealer or buy a Bosch one from Amazon for about $12. When I manually activate the switch everything works as expected with two exceptions: the rear blower stays on at a very low speed when the engine and ignition are off, and the amber lights remains out.

I found a wiring diagram that shows two connection points which I hope to check out at some point. One is behind the fuse box under the passenger seat, and the other is under the headliner at the rear left of the vehicle. Inspecting these might be easier said than done so I'll see how ambitious I'm feeling over the next few days/weeks.
-Michael

 

[mikem]

I resolved the issue with assistance from a local shop. They pinpointed a corroded wire in the harness located under the floor trim by the front passenger door. The rear AC unit now works.

Here are some details from my experience.

Tools used: Wiring diagram, Multimeter, Lisle relay tester (Lisle 56820), Power Probe 3
I managed to access most of the connectors extending from the battery to the control unit over the rear passenger seat. There were a few components and connectors I did't feel comfortable accessing.

I verified that both the blower motor and blower control modules were working. However, the relay for the rear AC wasn't activating. I connected the rear AC relay to the relay tester and measured the voltages across its pins (while the engine was running). For comparison, I did the same measurements on the relay from the front AC unit. I observed a discrepancy in voltage on pin 85 of the rear AC relay when compared with the front AC unit's voltage changes.

For the front AC unit's relay:
Pin 85: ~14v (off) and ~0.8v (on)
Pin 87: ~2v (off) and ~14v (on)

For the rear AC unit's relay:
Pin 85: ~14v (off) and ~14v (on)
Pin 87: ~2v (off) and ~14v (on) *this is when I manually activate the relay switch as noted in the pics above.

I was able to verify the rear ac relay worked by doing a few tests. I also confirmed the persistence of the rear AC unit's issue by swapping the relay from the front and rear ac. I chose to hit up a local shop with the info to this point and they were able to quickly find the corroded wire and complete the repair.

For those facing similar problems and are comfortable diving into the trim and exploring potential issues in the wiring harness there are open circuit testing kits available to help you identify the issue.

Hope this helps.