A question about the rear HVAC unit

Kirkz28

Original poster
Member
Aug 28, 2012
20
I should know the answer to this, but I just want to confirm. In a Trailblazer EXT does the rear HVAC unit actually produce heat and a/c, or just a/c (assuming it's working correctly, of course :wink:)?
 

CaptainXL

Member
Dec 4, 2011
2,445
Kirkz28 said:
I should know the answer to this, but I just want to confirm. In a Trailblazer EXT does the rear HVAC unit actually produce heat and a/c, or just a/c (assuming it's working correctly, of course :wink:)?


The rear unit doesn't produce heat or A/C. The engine produces the heat and the A/C is produced by the A/C compressor which is mounted to the engine. The rear has a heater core and a evaporator coil for the A/C. It's not a separate mechanical system.
 

Kirkz28

Original poster
Member
Aug 28, 2012
20
CaptainXL said:
The rear unit doesn't produce heat or A/C. The engine produces the heat and the A/C is produced by the A/C compressor which is mounted to the engine. The rear has a heater core and a evaporator coil for the A/C. It's not a separate mechanical system.

Sorry should have been more clear in my description. But at least you confirmed that I should be getting hot and cold air out of the rear unit! Thanks!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The temp actuator back there can go out the same as the front. A recalibration sometimes helps - often not. Assume you've seen the picture I've posted a hundred times about what it looks like behind the panel?
 

CaptainXL

Member
Dec 4, 2011
2,445
the roadie said:
The temp actuator back there can go out the same as the front. A recalibration sometimes helps - often not. Assume you've seen the picture I've posted a hundred times about what it looks like behind the panel?

Why are you assuming he has a problem? He never asked for advice. Just a question about operation. Aren't you supposed to be policing the many threads we have on this forum? lol Good advice anyways.
 

Kirkz28

Original poster
Member
Aug 28, 2012
20
the roadie said:
The temp actuator back there can go out the same as the front. A recalibration sometimes helps - often not. Assume you've seen the picture I've posted a hundred times about what it looks like behind the panel?

I have now. :biggrin: Thanks.

I'm pretty sure the problem is a lot simpler than that. When I bought the vehicle we plugged the a/c line as it was leaking, and we were in no hurry to replace it (summer over). I'm guessing the heat line has also been plugged, cause there is no heat from the roof vents and third row vent. Time to go investigate!
 

CaptainXL

Member
Dec 4, 2011
2,445
Kirkz28 said:
I have now. :biggrin: Thanks.

I'm pretty sure the problem is a lot simpler than that. When I bought the vehicle we plugged the a/c line as it was leaking, and we were in no hurry to replace it (summer over). I'm guessing the heat line has also been plugged, cause there is no heat from the roof vents and third row vent. Time to go investigate!

Im sorry. is this a continuation from another thread? I am just lost here. You never said what type of problem you have.
 

Kirkz28

Original poster
Member
Aug 28, 2012
20
CaptainXL said:
Im sorry. is this a continuation from another thread? I am just lost here. You never said what type of problem you have.

Sorry - thought it was clear from my last post. No heat from the rear unit. I just wasn't sure if the rear unit actually had heat capabilities or not. Now that I know I should have heat, I can work on why I don't have heat.
 

CaptainXL

Member
Dec 4, 2011
2,445
Kirkz28 said:
Sorry - thought it was clear from my last post.

Nope definitely was not. You should have said "I don't have rear heat...HELP!!" Would have been much clearer. lol. It's ok. I guess Bill just has a xray vision for these things.
 

Mooseman

Moderator
Dec 4, 2011
25,184
Ottawa, ON
Could be one of two things. An actuator in the unit, as explained by Roadie, could be toast or the heater control valve is stuck. It turns off the coolant flow to the rear heater core when heat is not called for. Run the engine until hot and turn on the heat front and back. Feel the hoses going into the rear heater core located just above the exhaust resonator. If it's not that warm, then that valve likely needs to be replaced. Not too expensive, about $20 at RockAuto.
 

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C-ya

Member
Aug 24, 2012
1,098
Is the control valve for the rear heat vacuum actuated? If so, it could be a vacuum leak. Given their penchant for electronic controls, I would doubt it, but I thought I came across that somewhere.
 

Kirkz28

Original poster
Member
Aug 28, 2012
20
Thanks for all the help folks! I won't get a chance to dive into this until the weekend, but at least now I can troubleshoot several things. :thumbsup:
 

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