Not much heat — 2001 Tahoe

[deaconblues]

Since it started getting cold up here in Maine, I noticed that my Tahoe ( 5.3 ) wasn’t putting out much heat (it gets warm, but only when directed through the a/c vents). After talking with several people who own Tahoes, I was told “heater core flush”. This is something I can do myself, but given the outside temps, I decided to take it to Meineke. They flushed it and replaced the thermostat, too. Still no freakin’ heat. The guy at Meineke says, “Your dash control unit must be bad”. He ordered one but never called me so I said screw them. I found a used one at the salvage yard and replaced it. Still no heat. No, I’m pissed because today I started it, let it come up to temp, and felt the lines going into the core. Inlet is too hot to hang onto, but the outlet is nearly cold. Could this mean that Meineke never back-flushed the core? Or, could I have a blend door problem? I’m thinking no on the blend door. I think Meineke screwed me out of $175 and that I wasted $70 on the replacement control unit. Opinions?

Thanks in advance. 🙂

Topic

[Matt]

The blend door won’t control heat into the heater core. There is a valve that controls the coolant flow. I’m not sure if it’s located inside the firewall on that truck or what, but if you can find a way to get an eye on it and see if the valve moves when you change the temp from cold to hot, that’s where I would start. If not, and since you already have replaced the head unit, then I would check for power and ground on what I’m guessing is an electrically controlled valve on a newer Tahoe. I’m assuming (terrible idea, I know) that the unit is electrically controlled if you just swapped out a head unit with a connector or two vs. disconnecting cables/vacuum lines.

What year is the truck by the way? Nvm, just saw it in the title.

[Matt]

I’ve been trying to find a heater control valve on parts sites to get an idea what it looks like/how it’s controlled etc, and I can’t seem to find one. So, my original post might be a wash. Here was my thinking though. You are getting hot coolant to the core, and apparently no flow through it. So I’m surmising that the valve isn’t opening, or Meinecke managed to clog it. On the other hand, you said you are getting some heat, so you may just have air in the cooling system, which is the most common cause of low heat (if it is the same on every vent setting, like defrost vs. heater vs. vents). Here is Eric’s video on bleeding a cooling system:

http://www.youtube.com/watch?v=zUpXgAJ1gjU

[johnzcarz]

+ 1 on Beefy’s reply and I’ll add that some vehicles don

[deaconblues]

Thanks, guys. I watched Eric’s video before I registered here. It doesn’t look tough to do at all, but if Meineke didn’t do what they said, or did it poorly, then IMHO, they owe me a real flush at the very least.

I’ll also try the bleed approach to check for an airbound system. 🙂

Now, I’ll have to see if it has a valve, and where the bleeder is located.

[college man]

I’m curious to ask.you say that you only get some heat from a/c vents. Does the air transfer to the bottom when selected? If not then you have a blend
problem or control problem.can you verify that when you move the selector switch to top or bottom air does come out? this way that will eliminate
the door selector. next Pull off the two heater hoses and flush through the heater core with a garden hose to see what comes out. (note when you
pull off the two heater hoses from the engine.see if theres a pipe coming from the engine to one of the heater hoses that you removed.these pipes
were notorious for clogging.while the heater hose is off stick a coat hanger or long screw driver down there to be sure its clear. If no pipe is there
then disregard this step and just flush the heater core.you will need to top off engine coolant and burp any system air.good luck and keep us posted.

[EricTheCarGuy]

The fact that one hose is hot and the other is cold means that there is no flow through the heater core. It could be a heater control valve issue as suggested but mostly those are found outside the HVAC assembly in my experience and are located in one of the hoses going into the heater core itself and are easy to check, I don’t know what set up you have on that vehicle however. It’s not to say that they didn’t perform the flush but perhaps they didn’t check their work when done as they should have. If there isn’t a problem with the heater control valve it’s likely to be an issue with debris in the heater core. You may try flushing it again according to the video I made you mentioned as it sometimes takes more than once to flush it out but I’ve run into some heater cores that were just too clogged to do anything about so you may end up having to replace it in the end.

[redfury]

Not entirely sure on the Tahoe, but my Chevy Astro has a control valve located on the outside of the heater core attached to the A/C condensor housing. You’ll know if you have a control, simply follow the heater core lines. One will go straight into the engine, the other one will go into a small assembly and then into the engine. That assembly is both vacuum operated and electrically actuated. The solenoid that opens and allows vacuum to open the valve goes bad. You can simply bypass the hose going from the valve to the solenoid.

That being said, there is also an electrically operated blend door actuator under the dash. It’s covered by a simple to remove plastic housing. It’s located under the dash, right above the transmission tunnel. It’s semi triangular in shape and has a metal circle with a slot in it. Take the cover off, and turn the key on. Operate your heat level control and watch the actuator. If it turns clockwise and counter clockwise, it’s good and you don’t have a problem allowing heat into the cabin from the core. If it doesn’t, then you may have a bad blend door actuator or control head. You can take it apart and figure it out pretty easily if you are somewhat familiar with how servo’s operate, it only takes 3 screws to remove it and one electrical connection. You can then take it apart and “reset” it if it’s bound up the gears. My MIL’s truck was doing that and for whatever reason if you turned it to full hot, it would bind. 7/8ths and it would be find. I think there was a problem with the limit switch or something else I never did figure out.

She also still had no heat after fixing that after a while and it ended up being a thorough flush of the core that did the trick. I’d do it yourself ( backflush ) and see the flow for yourself. You can bypass the heater core and drive the van if you need to do it someplace like a car wash, etc.

[Author]

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