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HVAC Frustration

I have a 2000 Silverado that won’t adjust cabin temperature. I was initially told heater core needed replaced. After further investigation I discovered the blend door wasn’t moving when the switch on the dash was turned from hot to cold or cold to hot. I found that I had heat when I manually turned the blend door. I replaced the blend door motor but the blend door still wouldn’t adjust. So I replaced the climate control switch on the dash. The blend door still won’t move. I have resorted to manually adjusting the blend door to cold in summer and hot in winter. What else could be causing the blend door to not adjust?

Is the blend door motor the same as an actuator? If so probably the blend door itself is broken.

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Blend door actuators are a common complaint here, so you are not alone. First off all, the obvious, have you checked all the pertinent fuses? And do any of the other blend doors still work? After checking that out … hmmm … Is it possible to just connect the actuator motor to the wiring harness but leave the blend door disconnected from the actuator? Edit: See caution post by insightful below. If so, try that and see if the actuator motor is moving when the controls are switched. If the actuator won’t move even without being connected to the door, then there’s a problem in the wiring harness or connectors between the hvac controller and the motor, or perhaps a driver transistor in the hvac controller is blown.

One more thing, on some vehicles the door actuators can get confused what position they are in, and require a homing procedure be done. I’m not sure if this is something a diy’er can do, or if the dealership’s chevy scan tool is required.

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There are a few youtubes on this. Did you re-initialize the motor when you put it in?

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On some cars, this will destroy the actuator, It must be installed before actuating.

Thanks everyone for the replies. I checked all the fuses I thought were pertinent and they were all ok. I didn’t know there were more blend doors to check. How many are there and where are they located? I’m no mechanic, so I don’t know about homing or initializing the actuator. I did try the actuator without it being attached to the blend door and it did nothing. Is my vehicle one of the ones that will ruin the actuator by doing that?

It seems it’s either the actuator or the power to it. Here’s a video for a Chevy Tahoe:

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You will do no harm by doing this

You need to hook up your multimeter and see what signals the actuator is getting when you turn the temperature control knob

There aren’t. You only have 1 blend door, because you have single zone ac

However . . . there are other actuator motors controlling other hvac functions. For example, an actuator motor controls the mode door.

Please elaborate. Exactly what do you mean by switch? Is this what you’re referring to?

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Yes, that’s what I’m referring to. Are these other actuators located behind the dash? If so, I’m out. I’ve done about all I’m mechanically inclined to do. Guess it’s time to pay out the nose for someone else to fix it. I’ve owned Chevy pickups all my life and they’ve all had some kind of stupid issues. Any recommendations on a brand more reliable than chevy?

Yup

I believe you’ve got an electrical problem, as you were able to manipulate the blend door by hand, if I understood you correctly?

Your truck is actually pretty easy to work on, parts are plentiful and cheap, and you can easily locate service information for free. Not so much the case with some other brands

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I doubt there are any. The problem isn’t Chevy so much as that car buyers these days want perfection. Including a perfect hvac system. it has to keep the temperature perfect at all time and at all locations in the vehicle. That requires a complex system, and complexity breeds unreliability. For comparison the hvac system on my 46 year old Ford truck works as well now as it did on day 1. Never has needed any repair at all. All the actuators are mechanical, rods, linkages, cables, etc. The compromise; the fan makes a lot of noise, and it doesn’t hold the cabin temperature to a constant perfection anywhere, let along everywhere. But its good enough. My Corolla is more youthful, 25 years, and the hvac system has never been repaired, works fine except that blower speed number one of four doesn’t work. Again all he linkages controlling the doors are mechanical, no electrical actuators. Are you seeing a pattern? lol …

Blend door problems are a very common occurance reported here. In most cases it is a simple fix b/c the door that tends to fail is the one that’s easy to access. Just replace it and drive one. Unfortunately some of the door actuators aren’t easy to replace and may even require removing the dashboard.

Ok so here’s a follow-up. I read where the two hvac fuses (1 under the hood and 1 left side of dash) could be removed, the key turned to the on position for a few minutes, turn the key off, reinstall the fuses to “home” the blend door actuator. I did that and it worked! Unfortunately I have very little heat. On low fan speed, it is fairly warm. But as fan speed increases the air becomes cooler until almost no warmth at all. I feel some background is warranted here. 2 winters ago I took it to the mechanic for this very issue, he said heater core needed flushed, which he did and it worked. Last winter I had no heat and took it to the mechanic, he said heater core needs replaced for $1000. I declined. That’s when I discovered the blend door wasn’t moving and when I manually moved it I had heat. Now, the blend door is working but there’s very little heat. Does the heater core need replaced? An acquaintance told me he had no heat and his mechanic told him his water pump was bad. He replaced it now he has heat. Could low coolant, air bubbles in coolant, bad thermostat, or bad water pump be responsible for the lack of heat? I really don’t want to remove the dash to replace the heater core if I don’t have to. Thanks for all your help so far!

Of course any one or all of those things could lead to lack of heat. There are diagnostics you can perform to try and narrow it down.

Go get the truck fully warmed up. Put the heat on medium fan speed and full heat from floor. Lift hood and feel both heater hoses. Are they both quite hot? Is only one hot? Are neither hot?

Only one hose for the heater core is hot. The other one is cold.

Is there a valve that controls flow to/from the core? If so, it is closed. If no valve, the core is plugged. (All this assuming you have the cooling system filled to capacity and any air burped from it.)

RockAuto.com shows a heater valve, but that’s no guarantee you have one:

Picture 1

A diy’er can usually figure out a way to run a garden hose through the heater core both ways to determine if it flows ok. If that works, then hook up the inlet but leave the outlet hoe disconnected and start the engine and see if any coolant comes out at the outlet. If not, disconnect the inlet hose and see if there’s any coolant to that point. One common reason for no heat when the thermostat and water pump are working ok an air bubble in the heater core circuit. It’s often the lowest point in the heating system, and an air bubble gets into that area , if big enough, will block all flow to the heater core.

I don’t have a heater valve. Coolant is filled to capacity. Not sure if I bled air from the system the right way. I drove the front of the pickup onto ramps so it was elevated and ran the engine until it was at normal operating temp with the heater turned on to high. Didn’t change anything. Still starts out as barely warm air that gets colder as fan speed increases.

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I will try flushing the heater core as soon as i have some time. Thanks for the advice everyone. Maybe someday I’ll get this fixed.

That works on most vehicles. There are a few it doesn’t, mostly low slung sports cars, which require some extra steps. There was a poster here with a Nissan truck that required a very unusual sequence of steps to bleed the air from the coolant system. I doubt anything like that applies to your 1500 though. The radiator cap was removed when you did that ramp-based air bleed, right? If so, I doubt air in the cooling system is the problem.