Yukon 2004 Rear Heater blows cold air only
I have a Yukon 2004, just recently purchased... rear heater blows only cold air. I bought the Hayne's DIY repair manual - $27 - but after I tore off the plastic shrink wrap and read the section for Rear Heater/Air Conditioning - Automatic controls, I was real disappointed to read that these systems are beyond the scope of the of a DIY'er sort of person, apparently. You can totally tear apart the entire engine though, right down to the bare block, bore it out it, reassemble it, all with painstakingly detailed steps and photographs... but a rear AUTOMATIC heater? Whoa, that's going to be way too complicated, dude! Maybe I should have bought the Chilton's manual instead.
72 Ranger - thanks for your teardown info, your remedy, and the photos you posted. I still managed to make a few errors though. First I thought I'd just pull off the heater actuator and have a look at it. It seemed to be stuck in the cold air position. So I used a large flathead screwdriver to rotate the socket to the hot air position. If you listen while forcing it to turn you can hear the gears and motor spinning. I went too far though and ended up seizing the gears way past the hot position (the actuator therefore has more range than the flap it controls. Up to that point I was not sure at all whether or not the actuator was previously functional, but I tend to think it was functional. Anyway, the next thing I noticed was the other actuator had all the same part numbers on it; so I used that one in place of the one I just broke. The heater controls now worked! Yeah, I could get hot air or cold air and any temperature in between. So I ordered a new actuator the next day (today) and installed that in the airflow control actuator location. Everything worked great. I ran the truck for 15 minutes while trying all the settings from the rear controls. Everything was fine. Then I drove around a bit, running a few errands, and parked, and thought - I'll just check the heat again. I wrested control from the rear by switching the fan control off AUX on the front overhead console, adjusted the front heat control to maximum heat and the airflow to above and held my hand over one of the rear vents and waited for hot air... only to feel cold air blowing constantly, again. I switched it to cold then hot... nothing, cold/hot/cold/hot... nothing. Then I can't remember all the other useless things I did in hopes of stumbling on some magic combination. Nothing. Unbelievable! Incidentally, these actuators cost $131 apiece. And I'm thinking I either wasted that cash because the problem is somewhere else, or something is frying the actuators after a bit of use and I've only just begun to throw cash at this problem. I felt like just giving up. I went inside and gave the bad news to my wife - she was not impressed at all. Berated (but motivated again), I went back out and tore it all apart again, but no new ideas came to mind - I stared at it all quite blankly. For a long time. It shouldn't need recalibration because it was working fine. But then I thought maybe the way I reverted control to the front had something to do with it and the cold position is a default position or something of the sort. I thought just disconnecting the control module (in between the 2 actuators) should be the same as removing fuses, so I gave it a try. Waited 10 or 15 seconds before reconnected them (like I read somewhere). Started the vehicle and waited while watching the actuators. The airflow immediately went to the full on floor position, stayed there for 5 or so seconds, then went back to the mid-point that that knob was set to - all by itself. Then the Temp actuator went to full heat for the same 5 or so seconds, then it returned to full cold, all by itself. I checked the temp knob and that was what it was set to. I turned the knob to hot and this time the actuator moved - hot air! Next, I switched the controls to the rear (AUX) and operated the actuators - all fine. Then I turned off the rear controls with the off button before turning the front fan control off aux. This time it operated from the front with no problems at all. I think my actuators were fine to begin with (I wish I hadn't broke that one) and just needed recalibration. Further, I think if the rear controls are on and set differently then the front, and you take the AUX off, that forces whatever settings are on the front control to immediately interrupt/change everything in the rear. Maybe that's confusing the system? If this is indeed a possibility then I think the system is at least a little bit flakey. I'll just have to take care that the rear controls are off before switching to the front controls. This could be a control module issue I suppose - but its working now even though it remains a bit on the fussy side.
A couple of notes - the GM dealer where I got the actuator was kind enough to print off an exploded view of the heater/air conditioner assembly along with all the part numbers. That was very helpful in understanding how the air flows and what the flaps do; didn't explain any of the weirdness of course. And imagine, that print-out only cost $131! Also, two of the parts had service bulletins associated with them - the heater control module(operates both actuators) was one - but the actual bulletins were not part of that print off. It just noted that a bulletin was issued at some point in the past. Would be nice to read those bulletins I think. The parts counter couldn't retrieve the bulletins.
