Powerseat and aircon intermittent

[MacNoob]

The power seat module also contains the temperature sensor for the A/C. I believe it's located under the seat. It may have a poor connection due to corrosion/age. I did have to have one replaced on my '07 fairly early in the car's life to fix an issue with A/C&heat not working properly.

[hoonk]

The power seat module also contains the temperature sensor for the A/C. I believe it's located under the seat.

I'm not aware of a temp sensor under the seat, there is one behind the small grill in the CCM on the dash for the inside temp, one in the evaporator for evaporator temp, and one in an outside mirror for outside temp. (there is actually a sensor in each outside mirror, but only one of them is for the climate control)

[MacNoob]

I haven't looked at the block diagram for ACC, but I know that the driver's side power seat module was replaced on mine to correct an issue with ACC. Makes sense to me that for dual zone to work, there needs to be some kind of sensor on each side of the car.

[hoonk]

I haven't looked at the block diagram for ACC, but I know that the driver's side power seat module was replaced on mine to correct an issue with ACC. Makes sense to me that for dual zone to work, there needs to be some kind of sensor on each side of the car.

I agree that makes sense and There used to be 2 temp sensors with the 850s, a left and right temp sensor that were in the ceiling near the grab handles (there were little fans in each of those, sucking air past the thermistor), then Volvo changed to the 1 interior sensor being in the CCM (with a little fan pulling air in)

[hoonk]

The power seat and aircon are intermittent. I can make them work by taking out fuse 24 and putting it back in but this only fixes the problem for a short time.

Looking at the attached wiring diagrams for the PSM and CCM - note that fuse 24 powers the relay marked 2/29 in position cmi22. That relay powers both the CCM and the seat module. (don't know what else it powers.) Perhaps you simply have a bad/erratic relay on the CEM (central electric module)

On this diagram is the position of the possible erratic relay on the CEM for the seat module and the CCM.



CMI22 is the 3rd one down from the top on the right column - try swapping that one with almost any other relay in those two columns (most of them are the same, match the part numbers) and see if your problem is fixed ( and possibly have something else stop working if the relay is bad!) Be sure to mark the relay you take out of position cmi22 so you don't forget which one was (possibly) bad.

[Astro14]

I was thinking "CEM" when I first read this...and the fact that the relay controlling both resides on the CEM makes me more confident in suggesting that you likely need a CEM.

Xemodex. $600. Not cheap, but they do quality work.

I'm about to replace the CEM in my 2001 T5 because of the odd indications that I am getting...all of which come through the CEM...

[Mr Bagshaw]

Thanks for all replies. Will have a fiddle when I get a mo and report back.

[Mr Bagshaw]

Thanks for that but sadly I still haven't got to the problem. I also have a 2004 xc70 (with working seat and aircon) and tried removing cmi22 to check that it powered the seat but it appears not.
I also tried removing the relay either side of cmi22 to see if perhaps I had it wrong but still the seat worked.