05 Z71 with auto climate - no heat front or rear

[Dirtman65]

Hello! I'm hoping to get some help with this issue. I've had this 2005 Z71 Tahoe since 2016 and it's been a great vehicle. It's got 170K +/- on it. I recently did a bunch of work on it because my wife was talking about getting a new vehicle and I didn't want a payment book. Well now it's winter and the heat is not working in the front nor rear. As you can imagine, this does not help my argument to keep the tahoe even after just dumping $4k into it.

Here are the symptoms:
Blower motor blows cold air out of both front and rear systems.
Coolant is full.
Engine temp indicates 200 degrees on dash gauge.
Both to and from heater hoses are hot and about the same temp. (temp is 1...2...3... Ouch!)
Blend actuator was replaced about a year ago as was the blower motor control module and it has worked fine until recently.
When I push the recirculate button it blinks 2-3 times and then turns off. (will not stay lit)
Note: the temp sensor in the headliner has been making noise for a while now. I have a new one but did not install as everything was working up to a week or so ago.

What I've tried so far:
Re-calibrated the actuators by starting the truck, shut off the ac/heat system, turned off the truck, disconnected the battery, waited 10 minutes, grounded the positive cable to the negative, reconnected the positive terminal, started the truck, waited 5 minutes and turned on the ac/heat.
RESULT - still no heat.

Removed the blend door actuator(the one accessed from the passengers foot well that is on top of the transmission hump) and manipulated the door manually. RESULT - No change in air temperature.

That is where I'm at with it as of today. Still no heat. Any help is greatly appreciated!

Thanks!

 

[MassHoe04]

What was the recent work?
Anything involving radiator, thermostat, hoses, water pump?

If coolant level is where it should be in the reservoir, maybe you the heater cores are air bound (or the lines to them).
Big pocket or bubble of air can prevent the hot coolant to flow through the core.
You may need to burp the system.

 

[corvette744]

Do you have automatic climate control or manual.

 

[Fless]

It would be best to use a Tech 2 or other capable body code reader to see if there are any codes being set.

 

[Dirtman65]

I have auto climate control. I tried resetting it as described above but no luck. If it weren’t for heated seats I would be having to take out a small loan to get it fixed. It’s been cold here! The real problem is no defrost. I’ve had no check engine lights showing. Any help is greatly appreciated!

 

[Dirtman65]

MassHoe - I will look into burping the system as that sounds like an inexpensive fix. I haven’t done anything to the truck that involves cooling system. Both the in and out hoses on the heater core are hot. Both the front and rear systems do not produce heat.

Work I’ve done so far; rebuilt the ac system, the front suspension, fixed a few electronic “gremlins” (PRNDL indicator, door latch switches, drivers door control module, etc) New battery, alternator, belt tensioner. Nothing that involved draining the cooling system though.

 

[MassHoe04]

Blowers all working OK in the range from off-low-med-high?

If HVAC controls are controlling blowers OK, yet manual operation of the blend doors did nothing....
Can you get the covers off to feel the heater cores in the front and back to confirm they are getting heat to those points?

 

[Dirtman65]

thank you for responding masshoe. Blowers working fine but blowing cold front and back systems. I’ve have had the rear cover off and it’s not so bad to get at. I’ve read the front core is hard to get at. the aluminum in and out extending through the firewall both feel hot.

I think I was manipulating the correct door. It is the one accessed from the passengers side above the trans tunnel. I replaced that actuator a few years ago. If it was the blend door then I would think the rear system would still blow heat. It seems like it would have to either be a coolant problem or it’s getting bad info and not telling the system produce heat. It’s something effecting both the front and rear systems. That’s all based on my limited understanding of gm climate systems ;-)

would a faulty temp sensor in the headliner effect the temp outputs? It had been making noise for a year or more. Not sure if it still is or not. It was one of the things on the “honey do or I’m trading it“ list. I didn’t replace it because it was working ok and I was getting burned out from working on it so much. In fact, now that I think about it, I bought a new one and it’s still around here somewhere. Would that cause the no heat front and back?

 

[Fless]

I think that if you use the HVAC control on manual settings, the temp sensors in the ducts wouldn't be a factor. Not 100% sure, though.