Having issues with my 05 TL w/o navi 172k miles. Issues are located in the fuse box under the hood. My problem is that the relays for the a/c comp clutch, condenser fan, and radiator fan are not receiving their ground to turn on. I have checked the relays and terminals/sockets for the relay box and I am not receiving a ground for the relay trigger circuit. There is 12v on the load side and 12v on one side of the trigger switched side. I tried replacing the relay box/tray and still having the same problem. Does anyone know where the relay tray gets its ground from? Or does anyone have wiring schematics/diagrams. Any insight would be greatly appreciated! Thanks!

 

Load fan grounds are located at left front fender weld area in engine compartment.

AC clutch load ground is at right front fender weld area in the engine compartment.

Trigger grounds are by the pcm. Connectors A6 Low (condenser), A7 high (radiator), A27 AC clutch.

 

thanks for the quick reply ALCS.
so since all 3 (compressor+both fans) are not coming on, would you think that this is a PCM malfunction?? Does the pcm send the ground to the relay to complete the circuit? In the relay module/box I have a good ground and hot (+12v) on the load circuit and just a hot terminal on the triggered circuit, no ground.

 

Can't tell, not enough information to confirm that because the pcm receives input from various sensors and the climate control module.

Your assuming the pcm is not grounding. Which is correct but why is it not grounding is the question you need to answer?

Is it not grounding because of a defective pcm or because the pcm is not getting a signal from the climate control module, a sensor, and/or something else?

You have not given any information other than those three items are not working even though there are 2 hots and a ground. Are relays good, does the machinery work if you complete the power circuit, etc?

 

Ok, so I have tested the three items in question by jumping the load circuit, and they do work. I have also tested the relays that control them, individually, and they check out. When turning on the a/c, nothing happens as if I did not even hit the button. There is no idle change, no click in the relay, nothing happens at all but it does show the "a/c on" light in the dash panel. Additionally, both fans are a similar story, I have not heard either one come on.
Is there somewhere I could do voltage checks or resistance checks to verify the PCM is bad?
Thanks again!

 

Yes you can but too many variables to test because there are 3 modules. Gauge control unit, climate control unit, and ECM.

You would need a manual to test all of those items. And obviously way to much information for me to cover in a thread.

The most likely culprit is the guage control unit or the wiring between that and the climate control unit.

The ECM would be the least likely culprit since your TL is operational.

 

Do you think the gauge control unit would also cause the fans not to work? It just seems odd that all 3 items are doing the same thing, I feel like it would be a central malfunction that they are all 3 related to.

Also, if you had locations or pictures of where i could check it would help ot a ton.

 

Correction, I meant Display Panel Control Unit (DPCU ) not guage control unit.

Apparently the DPCU is a cpu that can control those 3 circuits and communicates with the ECM.

DPCU is your climate control display/infotaiment distpay. Ahh... $1800 OEM.

At that price I would suggest you obtain a manual and follow the diagnostic flow chats.

 

I'll look into it and post what I find. What a headache!! Thanks for the direction.

 

Update**************

Ended up having a broken wire to that goes from the relay control module to the a/c pressure switch (blue/red wire). Repaired the wire and everything works as bit should, finally!

 

 

Thanks for updating!

I was going to mention that the car won't send signal to those relays unless there is high enough pressure in your line.
Having a broken wire from the sensor would definitely make sense!

 

Just happy it's fixed, and a bonus it didnt break the bank, just took some elbow grease and digging!