Heater not working?

Easy solution, swap the truck with someone from Alaska. :-)

Actually the problem is likely a failed sensor. It is telling the HVAC controller that the interior temperature of your truck is already over 86 degrees.
One of the common ones that fail and cause this is the internal cabin temperature sensor, it is the thing that looks like a speaker in the headliner over the drivers door.
It has a tiny fan and a thermister inside. They suck in crud and it makes them fail.

You replace it by removing the interior windshield trim on the left side, the center pillar trim and handle and then the left side sunshade. Then you gently pull the headliner down. You will see the sensor. Disconnect the wiring connector and then the interior grill comes off.

ACDELCO # 22834330

On my 2006 GMC Sierra the a/c heater mode stays on vent even when changing the control to the floor or defrost positions. Also the highest fan speed does not work, all other speeds are ok.

its your control unit i belive. same thing happened to one of my friends 2008 chevy tahoe. you should try that.

I need you to check a couple things. This guide will help

https://www.2carpros.com/articles/car-heater-not-working

Let me know what you find.
Joe

Joe,
Thank you for your quick reply.
Where would I look for the vacuum lines under the dash? When I look under the dash no vacuum lines are visable. If it was a vacuum leak wouldent the the engine be running rough? There's no roughness that I notice.
Also a few monthe ago I was running the a/c heater blower on high speed when I started noticing a (electrical) burning smell, then it quit. The blower works on all other ranges but just not on the high speed. Could this be the resistor? where would I find the resistor.
Bill

I have attached schematics for you to review. The GMC model uses electric and not vacuum for some reason. Review the schematics to see if you can identify where to check under the dash. Also, as far as the high speed, it believe it is a relay rather than the resister. See schematic.

No heat on the drivers side of the truck

You need to open it up and investigate why-could be a door or an actuator problem-

2005 GMC Serria 1500: Interior heating not working on any setting, defoster not working too. flucuating water temp indicator jumping from normal to 30 degrees higher then back down to normal. Electric raditor fan is working.

Have you replaced the thermostat? Is the coolant full? As far as the heater, with the engine running, hot, and the heater on high, do both heater core hoses get hot?

One last question, is the blower motor working for the heater or is that the issue?

the heater will stop and start blowing warm air randomly. If you excellerate heavy it will start to blow warm air again and then randomly go off and blow cold air. The fan continues to run on what ever level you have it set on.

thanks for your help

check to see if your actuators are getting power or not. you may have a control head going bad. Also cleant eh battery cable ends as it may be making poor contact until you get more revs going to put a better charge int ehbattery. You might also check your battery , most auto parts stores can do this for free. i've included a generic pic of actuators.

A/C blows fine. Directional blend (defrost, floor, mid) works without clicks or hangup, record/fresh air works correctly, heater core is functional per readings on inlet/outlet lines, dual zone module has been replaced. Full console, AWD, Denali. What am I overlooking?
Or, how many blend doors need I chase on this model besides the two mentioned? Operating temperatures on radiator hose is 174-176. Operating temperatures appear to be reached.

Good evening.

What are the temperatures of the heater hoses under the hood?

Can you hear the blend doors moving when you command heat and cold?

Roy

https://www.2carpros.com/articles/replace-blend-door-motor

171/164 temperatures very close to firewall.
Yes on vent/acutator movement. With engine off, key on. Dialing full range limit to limit. I can hear several actuators in movement. One left side, one near center, one upper right of dash.

Okay, thanks.

It sounds like you have a clogged heater core. The temperatures are too close. There is usually a bigger difference it temperatures.

Try removing the hoses and flushing the core with a garden hose. flow it back and forth several times and see if get debris out of the system.

Roy

Thank you! I will get to it.

Keep us updated. Feel free to ask any follow up questions.

Roy

Much appreciated. Again, thank you

I realize this is quite late from last reply, although I finally did disconnect heater hoses at firewall and used garden hose and nozzle initially to flush heater core. Quite a few clumps emerged, particularly from return side. Continued back and forth several times until run clear. Used low pressure pressure washer with same effect. Reconnected hoses, topped off glycol, ran truck to temperature. Checked all vent options and sure enough heat! I was stoked, am stoked. Winter comes fast some years. I appreciate all the thought put into helping.
Again, many thanks.

You are welcome.

I have no heat and no blowing from the vents at all in my truck. changed the blower motor, still nothing. checked all the fuses and stuff, still nothing. got a brand new control module still nothing. got a new blower motor resistor still nothing, thought maybe the new resistor was faulty exchanged it for another, still nothing. There is power at the plug that plugs into the resistor, but it doesn't seem to be traveling through the resistor to the blower motor. like when i would test the resister plug there is no power, but the plug that plugs into the resistor has 11.8 volts power. anyone have some idea of what could be happening?

Good morning,

I attached a wiring diagram for you. Check the second fuse for power to the fan switch.

Then go to the resistor and see if you have power when commanding fan speeds. You should have power in each fan speed selection. If you have it, then check the ground for the resistor. I attached the location of the ground.

If you do not have power, then the fan switch is bad.

Roy

Thank you. i will check that out and see if it works.

You are welcome.

Always glad to help.

Roy

Heater works fine while driving quits blowing hot air when i stop. Truck has 5.3 vortec motor two wheel drive half ton. Ac works well just heater problem..


Thanks for any help you might be able to give me i checked the vaccume hoses seem to be connected

Is the coolant full? Does the air coming out get cold? Have you checked the blend air door?

Yes coolant is full ac works good and i dont know where blend air door is if something wasnt right with the door would it work ok when driving?

I am trying to remember if the blend air door was vacuum operated on the 04. It is located near the heater core and determines if you get heat or ac. If it is vacuum operated, yes it could work okay when driving. However, to me it sounds like you may have a partially plugged heater core. That would make more sense with the symptoms.