no rear heat 05 trailblazer ext 5.3l 4wd

oh05ext

Original poster
Member
Dec 7, 2011
166
on our truck we have no rear heat.i can hear the blower pushing air but dont know which control to check first.the front switch by the shifter or the one in the back of the console.is there a valve on one of the heater hoses in the engine bay to let the hot coolant flow to the rear that might be non functioning.ive searched and see alot of different problems with actuators etc..any help is apprecieated.
joe
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Check the Owner's Manual for details on the controls, but you're right. There is an aux valve (vacuum powered, electrically triggered IIRC) on the firewall where the hoses go through.

View attachment 19525

There is also a fix-it kit GM put out that adds a little electric pump to boost the measly hot coolant flow to the way back. Some owners got that retrofitted for free under some special extended service program. Probably long expired by now.

So see if your rear heater core has hot water going through the plumbing (you can also go underneath and feel the pipes.),

View attachment 19527

then confirm the hot/cold actuator is moving as expected when you turn the control. Take the rear right side interior panels off to look at this. The heat actuator is item 33.

rearactuators-orig.jpg
 

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oh05ext

Original poster
Member
Dec 7, 2011
166
thanks,ill check around while im doing the oil change today.looks like ill be tearing the rear apart.(insert sarcasim here) yay.
 
Oct 13, 2012
24
I have a related question on this topic. I have the same problem with the rear heat where I hear the rear blower running but no air comes out the roof vents, both with rear controls and front controls. sometimes when I first start the vehicle it will blow air then after a few minutes it stops. Same thing when I reset the fuse. When it does blow I have heat. I also have the GM aux pump installed by the dealer when I was under warranty. Does this sound like part #3 actuator?
 

wcrosthw

Member
Oct 1, 2013
6
I had the clicking sound & the 3 minute delay before the rear blower would kick on - replaced both actuators and did the fuse reset multiple times. I've listened & watched the actuators but they don't seem to be working. I'm getting cold air only when the heat is on? Any ideas? Could it be the blower control mod?
 

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