High Heat From Rear A/C Ducts w/ A/C On
 

Does anybody have the definitive cure for High Heat coming From Rear A/C Ducts when the A/C is on in the front? The heat from the rear absolutely overpowers the A/C, and you have to shut the system off to survive.

This ocurrs intermittantly in my car and my dealer really has no experience with the problem occuring in other cars since they work properly when the techs look at the cars.

Is there a positive cure for this ??? ... a TSB? ... a part number? :wall:

Do you have the answer MbenzNL Steve?

No part number, but...
 

it is most likely the heat exchanger for the a/c which is defective. It is located under the wiper linkage assembly.

Barry45RPM... the problem with your car is a faulty heat exchanger shut off valve. It is an electronically controlled valve attached to the heater core beneath the wiper linkage. There is a DTB regarding the issue with the rear vents blowing warm air. A few pin tests have to be done with the Front SAM prior to replacing the valve itself. In my exp. though, the valve has been the problem 100% of the time. I'll see if I cant find some part/bulletin numbers for you tomorrow.

Here’s the thing Barry mentioned this on several occasions and of course I understand you cannot answer for others however, why couldn’t someone at his dealership figure this out most especially since it was a repeat complaint? At least replace the part for precaution even if it is not actually witnessed. A bulletin exists that relates directly to the complaint, no grey area. Anyway, curious about the bulletin release date, I’m usually current with these things. Thanks.

Barry, if you had gone the route suggested (PM) can you imagine how embarrassed the service dept. would have been? Nevertheless still an ace in the hole that’s readily available if, and when needed. The way I see it you’re covered at least till year’s end with the gratuities, no? :D Good luck.

Cost estimates for part and repair labor?

EDJ

Thanks guys for all the help !!

Will watch the thread for part numbers/ bulletin... then its off to the svc dept for the repair. The heat is incredible and completely overpowers the A/C.

I don't want to embarass the Svc department since they are SO GOOD to me... and yeah, I am covered at least till New Years with gratuities. But I don't mind taking care of those that take really good care of me.

Barry, if you're worried about embarrassing the service guys, you are working with the wrong dealer. They ought to be grateful that you can provide the information needed for a fix and embarrassed by their failure rather than your calling it to their attention. If you simply politely point out the information and ask them to look at it, they won't think less of you for it -- they'll like that you have such an interest that you found the answer. There have been several times I have done this with my dealer. The tack to take is not to get angry at them which will make them defensive, but put yourself in the position of helping them think through the problem. Maybe its because I've dealt with my dealer since 1986 and keep returning to buy cars from them, but notwithstanding my explicit use of stuff from this forum (which is just terrific), they treat me very well, which keeps me coming back. In fact I probably "overpay" on each car by $1,000 but it is worth it to me to have responsive and responsible service.

+1. Had mine recently replaced. Allong with half the AC system since it was leaking refrigerant...

Any luck finding the DTB on this problem?

Same sh*t happened to me this morning on my way to work :smash: :smash:

DTB P-B-83.20/72 SEPT04
Rear A/C Intermittently Blows Warm Air in Cooling Mode or No Warm Air in Heating Mode.

Check the heat exchanger shut off valve, M16/32. DTCs 9026 (M16/32 open) and/or 9027 (M16/32 short circuited) may or may not be stored. A test via “actuations” in DAS may indicate that the driver side SAM is malfunctioning. In any case, perform the following test. Prior to replacing the driver side SAM, perform the following test.
1. Remove connector M4 from the driver’s side SAM.
2. With a multimeter, check the resistance between pin 9 and pin 12 on the connector just removed.
3. If the resistance for M16/32 is less than 10 ohms, replace the heat exchanger shut off valve. Do not replace the driver’s side SAM.
4. If the resistance for M16/32 is 10 ohms of more, the heat exchange shut off valve is OK. Continue to diagnose the system as needed.

Heat exchanger shut off valve part # A211 832 00 84

OK. GREAT WORK! Now I'm done roasting. Thanks for all your help. Amazing Job.

Thanks @konigstiger for the test instructions above.

However, I have a stupid question, I'm having a hard time figuring out which one is connector M4 on the SAM. I have searched, and I suspect it is something obvious that I'm missing, or I'm just too inexperienced to figure out? Can someone help?

Using SDS, Dr-Side SAM has a fault: 9026 "Component M16/32 (Heat exchanger shutoff motor) or the lead has a short circuit". My AC and heat seems to be fine, but I would like to determine if the problem is the SAM or the heat exchanger shut off valve.

Would appreciate some help on where connector M4 is on the SAM: do I need to remove anything else on the SAM to get to connector M4? Looking at the nest of wires with my old eyes, I couldn't easily find M4, and I didn't want to moving wires around without having some idea of what I was looking for...

https://cimg1.ibsrv.net/gimg/www.mbw...592773df76.jpg
https://cimg2.ibsrv.net/gimg/www.mbw...7f5c99dcc1.jpg

@konigstiger Once again, THANK YOU!!!!

I think my problem is solved... Again, I wasn't experiencing any problems with heat or AC, I just had a current fault from SDS of "9026 Component M16/32 (Heat exchanger shutoff motor) or the lead has a short circuit"...

I pulled the driver side SAM with the help of the pictures above, and checked resistance on pins 9 and 12 on connector M4 per the instructions above, and got 90 ohms (hope I was doing it correctly)... So I assume my valve is fine, and the problem was elsewhere (maybe the SAM...).

I was taking the car to the dealer for SBC replacement under warranty, so I thought I would simply have them diagnose and possibly fix this fault depending on the issue. However, the Dealer said when they scanned it there were no other issues?

Is it possible there was (or is) a bad connection somewhere, and when I messed with the SAM, the connection is now properly seated?

I plan to keep an eye on it, but for now my 9026 fault is gone...

Lee