Heated seats and rear heat / 2004 Z71

[bsweasel]

I have a 04 Z71 with heated seats and rear HVAC. Now that I just bought it in the summer and the cold is starting to set in in Michigan I find that the heated seats don't work and the rear heat is blowing cold air.

Heated seats: Driver side: push button, all lights go on then they automatically turn right back off.
Passenger side: All lights come on, no heat on seat, push drivers button and the passenger side lights go out.

Rear heat, fan speed and front/rear control work, just not the temperature control, its cold air no matter what.

I removed what I thought are the fuses in the engine compartment and in the dash and they both look good. No user manual with it so I don't have a fuse reference.

Anyone have a service manual or any ideas of a place to start????

-Brad

[J-Ri]

The rear heater sounds like a plugged heater core. Check the temperature of the inlet and outlet hose right next to the heater core. They should be close to the same temperature. If not, The heater core needs to be flushed.

Disconnect both hoses. Using a garden hose, spray water into the cold side until it comes out the other side clear. Reverse direction several times. You will probably want to flush the entire system, because if the heater core is plugged the entire system is probably pretty dirty.

[bsweasel]

Is there a separate rear heater core? I assumed it was an electric heat in the rear? I obviously don't know rear heat is new to me. The front is blasting heat just fine so if its only a single heater core that gives heat to front and rear that that is surely not it.

[J-Ri]

I am not aware of any vehicles that use electric heat. To be comfortably warm, you would be using more amps than a single alternator could put out.

Some vehicles use one heater core, and have an air duct going to the back. Although, I'm fairly certain yours has a second heater core for the back. Crawl under the truck, and look for a set of lines going to the rear. Depending on whether or not it also has rear A/C, it will have either 2 or 4 lines.

And I forgot to mention above, when flushing the heater core, blow compressed air through every time you reverse direction. Use short bursts so as to not damage the heater core.

[bsweasel]

Update: After reading other "rear heat" threads. I removed the passenger rear panels. This is done by first removing rear pillar panel with speaker. Pry it off gently with a screwdriver. (it is entirely snap in style connections) Then remove black knob for cargo net by un-screwing it. Remove screw on forward pillar that is resessed into hole for cargo cover. And then loosen it by prying it strait out. Then pry entire side panel away from window until it is out far enough to reach behind and remove wire from 12v accessory plug. Everything else that holds it is snap in like the ones that hold the pilar cover in. Remove entire panel.

There are two motors. the forward one controlls the gate to switch between floor and overhead vents, the rear controls the gate for hot and cold. Three silver screws hold them in place. I removed the the rear one. manually moved the gate using the shaft and bingo..heat. I placed the front motor on the rear shaft and then proceded to watch it move and over extend the range of motion, never to return to the correct spot even when re-connected to the front gate. Now it appears I have two bad motors and the rear control that breaks them. Anyone have ever fix this issue??

[bsweasel]

Update 2: Further investigation of above mentioned motors/actuators. I removed cover off one of the "black box motors" to reveal the actual motor, circuit board, and 5 gears. Thinking maybe I could revive it from it over-extended state. So I plugged it in, to the front connection while the tahoe was running control set to floor position with no cover on it. It moved all the way to the opposite side and stopped. There appears to be a sensor on the circuit board to detect the position of the gate. And it will turn automatically. If you remove the large black gear that connects to the shaft, it has two copper arms that go down and touch contacts on the circuit board, these seam to have grease on them that is the same as the grease used to lube the gears. Does anyone know if the gear grease is supposed to be on the sensors and if could it be the cause of this?

[WHATDIDYOUBREAKNOW]

Dielectric Grease

[bsweasel]

Wow what an informative reply.

Update: I took apart the front actuator and got the gear in the right position, re-assembled, re-installed and it now works for changing the air from floor to ceiling. But I'm back to square one on the Hot/Cold Actuator. I found an ACDELCO part that I think is right #1572972. Can anyone confirm or deny this as the correct part? The number is not listed on the one I removed. I do have RPO code C36 listed in my glove box if that helps.

[Redonthehead]

I too have the rear heat issue. I too have removed the actuator in the back. I fooled with the old one, then bought a replacement, installed it, and voila! still the same problem. I suspect there is an issue in the sensor(?) or control(?) that tells that actuator to move the door to heat. Let us know.

[bsweasel]

I received my new actuator, part number listed above on Friday, installed it while not mounted to the truck and watched it move back and forth and beyond the limit. I then un-plugged it and mounted it, plugged it back in and it worked flawlessly. I'm thinking there is a resistance sensor or something? Anyway, with the new actuator, the hot/cold now works. I've re-assembled the interior covers and all is working well. For those who read this later I hope this helps.

FYI: The Delco part was $80 plus shipping from www.rockauto.com. My local stealership wanted $149.00

[bsweasel]

I'm really tired of this heated seat issue never got any replies and never investigated since my first post. Any newcomers who can comment on Drivers side seat heater that works every once in a great while. Most of the time I just hear a faint click that sounds like its coming from the dash when I turn it on. And it immediatly shuts off. Passenger side seams to work all the time, although its rarely used.

[Bruceman07]

might have an answer for ya on the heated seat prob, if this is still open get back to me with details, how many heater buttons, where located, leather, cloth etc.