2004 Tahoe with dual climate control. For some reason I'm only getting AC (cool air) but no Heater. I adjust the temp all the way up (90degrees) and the system "switches" to under-dash vents (like it should), but there is no change in the temp of the air coming out (still ice cold). The vehicle has independent rear climate control as well, and it is remaining "cold" when I try to up the temp (set rear to 90degrees) in the back as well.

What would be causing all the system to be "cold" all the time? Engine coolant is hot (165-180) and all hot water lines (both under the hood and out back at the rear HVAC unit) are hot.

I have read about how other people have the temp-door actuator go bad (seems to be quite common) but I'm not sure how you go about replacing it. It almost looks like the entire dash would have to come out. I would guess the rear has an actuator as well?

What sounds like the problem and how do I resolve it?

 

I am stumped on this one. It could only be a few possibilities......

1) It is the blend door actuator like you said but it would be rare that all 3 would go out at the same time even though they are common problems. (You have 2 in the front for the dual climate control and one in the rear if you can change the rear temp independant of the front.)

2) It is the climate conrol it self, but usually if they go out it will default to heat not to a/c. (the unit in the dash that you control everything with.)

3) It is a broken duct where the actuator motors attach. Sometimes the duct can split so the motors just spin in the hole without actually turning the blend door. (Again I wouldnt think all 3 would break at the same time however)

These are the only 3 possibilities I can think that it would be. The fact that both sides of the front and the rear are all a/c would lead me to believe if might be number 2 and that it has just defaulted to full a/c instead of full heat as I have seen in the past. Can you play around with the controls from side to side and make it do anything else out of the ordinary??

 

The front mysteriously started working (adjusting for both hot and cold) last night. I had been driving for a while and when I got home I decided to just flip it to heat and see what happened. I did notice it took a little bit of time (min or so) for the heat to kick in. In my Reg Cab Silverado (manual adjust dual climate system), the system responds almost instantly. Perhaps the front heat was "working" but I wasn't being patient enough to give the heat exchanger time to "warm up" when I tested it yesterday morning.

The rear however is still blowing cold. I got under the vehicle and confirmed the hot water lines to the rear are indeed HOT (they are). I left the system running for a good 5 mins but the rear never did get hot. I'm going to take the rear trim panel off and see if the door actuator is bad (seems so at this point).

Side question:
IF I had to replace the front actuators (say 6 months down the road), what's the process? Does the dash have to come out?

 

I dont think it does unless they went with a totally different duct design on the dual climate control set up. On my truck (02 rcsb) the blend door motor is righ below the cupholders facing the floor. I would bet the motors would either be there or possibly behind the glove box.

I will look the job up in my dads labor manual tomorrow and that will tell us based on the number of hours if you have to pull the dash or not.

 

Well I think I might have found the problem. Today while I was driving the tahoe started running hot (215). Fans were on full and it would "cool" when idled up. Come to find out the cooling system was about half empty (required several gals of water to fill it up). How it "lost" that much water I have no idea since there are no "wet spots" under the vehicle. I can only imagine that I didn't get the system fully filled when I swapped in the radiator (perhaps it had air back in the heater lines and such). Crazy.

 

Yeah that is probably all it was. On those it is sometimes hard to get all the air out of the heater core when filling it back up with antifreeze. Several times at the shop I have let the vehicle sit over night so It would burp all the air bubbles out then I could fill it up the next morning. Glad thats all it was though.