Rear heat sketchy in 2003 Z71 Sub...

CPT Furious · December 12, 2006

To all,

I hope someone can help me a little here. I'm not at home right now, but my wife has been telling me that the rear heat in the 'Sub is not all it used to be. It is a 2003 Z71 Suburban and with the truck fully warmed up, the front will be as hot as you want, but the rear will blow cold air. Sometimes it might get luke warm, but it's not always consistent.

It looks like there is only one tap off of the coolant system in the engine bay, but is there a separate circuit for the rear system? Is there a way to bypass it so it gets hot coolant? It's 20 F outside and with young kids, I want to keep them warm!

Any advice on where to look/troubleshoot?

Thanks!

GM-Tech · December 12, 2006

Go underneath in back and first see if both hoses leading into and out of the heater core are hot.

CPT Furious · December 17, 2006

Just got back home...I'm going to check tomorrow. I also picked up a Haynes manual, but is there any kind of manual that is more detailed? Like a factory approved repair manual?

CPT Furious · December 20, 2006

Okay, finally got some time to troubleshoot today. First of all, when I turned the rear heat on today to check it...it worked! Figures. Anyway, there are four lines under the truck running to the back (2 for heat, 2 for the A/C I assume) and the two heater ones were hot! So I think the core is good. I also pulled all the interior panels out of the back to get to the blower/heater core/evap unit and have some questions.

While adjusting the temp, the rearmost one would move, so I assume this is the temperature control valve and that hot water is always flowing back there since I didn't see any kind of water valve.

While adjusting the floor/foot, the forward most valve would move, so this seems to be the flapper for that, but it looks like the exact same one and the bar codes on the two are the same so are they the same part number? Are they interchangeable in a pinch?

Also, if I get desperate, can I manually set the heater flow one for full air flow through the core and disconnect the electrical connector so I can have heat and it won't move?

Thanks!!!