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2000 Z71
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39 Posts
Discussion Starter · #1 ·
Ive read several of the current posts and some random google searches and not sure if this is linked to the other issues Ive read. 2000 silverado SL package. In short....when the rotary temp knob is set to hot, cold air comes out or for A/C ops, and when it set to cold, the air is hot or the heater works. A Vac line reversed somewhere maybe?
Thanks in advance.
 

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Electric air blend motors are used to direct the air through the HVAC system. They are mounted on the driver and passenger side of the HVAC plenum. (you'll need a manual to verify which is what)

One of these motor assembly's was probable changed out and the incorrect P/N was used to control the main internal door that directs the heat/AC.

I have had this happen to a Buick I owned. The motor was bad, the shop ordered the incorrect p/n and installed it. It fit but operated in reverse of what it should have done. They corrected the problem. But on that car there were, IIRC, 6 different units installed on the plenum.
 

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2000 Z71
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Discussion Starter · #5 ·
Sounds like the culprit. But geezzz..I looked up on a on line supplier and there are like 10 or more different motors from each of several suppliers. Guess I need to yank it and see if it has any GM numbers on it. Thank You RivGuy.
 

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2000 Z71
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Discussion Starter · #8 ·
Sorry for the delayed response. The answer is NO. Several months ago the heater core went out. After seeing what a PITA is is to R&R I took it to a shop recently now that its in the single digits where they replaced the heater core and the 3 control motors with GM parts. Now I have only hot air all the time coming from the defrost and if the blower is on 5 the air output is probably half what it should be.
We then suspected the control module which was swapped with a used unit. It seemed it functioned somewhat for a minute then crapped out back to the same. I question the used junk yard module anyhow. After doing some more digging I found a U tube vid on silverado defroster stuck on. Its some 30+ mins long but has some good info. In short the mechanic tested the system and wiring best as possible considering GM's lack of tech data to trouble shoot and found the drive motor for the floor/dash/ defrost not moving. The system is run off 0 to 5V., 2.5 is the dash IIRC, 5 the defrost and 0 the floor.
For lack of a better explanation the motor drove past its 5v limit voltage to where the feedback to the module basically didn't know what to do and no longer responded to inputs. I saw this personally on the electronic equipment used to test. The way the HVAC box is made the foam on the blend doors stops the drivers below or at the max 5V output voltage. With the foam gone the flap or door and motor traveled past that point, the feedback exceeded 5V and the module went out of bounds. Instead of the drive motor having a stop, the blend door is used to stop the drive motor.
The mech removed the bottom left side drive motor and put a screw in the slot to stop the motor from exceeding the previous travel point. This kept the feed back signal to the module below 5V, and everything then worked as it should. Bottom line...more garbage engineering from GM and China made OEM drivers and parts. I know everyone here is pro GM, thats what we have GM's which is all I've ever owned more less for 45 years. Never again after this piece crap of an excuse for American made or "like a rock" yes, straight to the bottom of the sea is where todays Chevies should be.
For the how are chevies these days here is what failed between mine and a friends.
Transmissions, Oil pump O ring, heater controls, dash/speedo/gauge cluster, Transfer case rub issue, Intake gaskets, power seat motors, window motors, ebrake system self destructing, broken exterior door handles, leaking windshield gasket. Then we still have the piston slap and failing lifters that will never get fixed by me at least. I sold my square body years ago to "upgrade", Im still kicking myself in the ass. :mad:
 

· SilveradoSierra Guru
2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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Sorry, I can't say for sure about the actuators for your '00, as they might be different, but the ones for my '04, they have mechanical stops on them, and I've watched them go from stop to stop to make sure they work properly.

Actuators, power seat motors, window motors, door handles, these are all things normal people aren't surprised if they fail over the course of 25 years.

What lifter problem with your '00? The engine is almost 25 years old, and I haven't heard of any kind significant issue with them.

And the full-service manual for my '04 has pretty good details of how the hvac system works, and how to diagnose problems.
 

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2000 Z71
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Discussion Starter · #10 ·
There is quite a bit of info regarding the piston slap and lifter failures on silverados. In my case lifter bleed down is the issue when it sits a few days. Fire it up and it runs on 5 or 6 until the lifters pump back up. My BIL also bought a new 2500 in 02 and right off the get go it had lifter issues. Ive owned 200 different vehicles in my 48 years of driving/wrenching and all of them have been pre 2000 except for the new 07 2500 I bought. 25 years old means nothing as far as stuff failing because most of my vehicles are old and do NOT have piles of cheap made blingy pointless china electronics on them.
In August of 2021, a class-action lawsuit was filed against General Motors (GM). The allegations discuss problems with the engine valve-lifter in the Buick, Corvette, Chevrolet as well as the GMC vehicles equipped with Small Block V8 engines. granted this was specifically for the AFM vehicles. Another GM failure Ive seen first hand unless replacing a engine around 100K is considered "good service" by some. A new GM crate engine was about $1700 a few years ago. 100K was good back then from a engine. Today we can get 300K from an engine, but you'll spend 10K+ in repairs as the rest of the damn things disintegrates around the engine.
 

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Discussion Starter · #11 ·
Still trying to get things going here with regard to the HVAC on our 2000 Z71 with manual HVAC controls. BTW, it sorts worked pre heater core R&R. New core, 3 new drive motors, new module. Blower works fine but still no control of where the air comes out and its stuck on hot air out of the defroster. Ive read endless pages of others saying you have to set the door motors in the middle of their travel of they will go off the end of their voltage travel and become non operative. Im stumped and cant throw any more $$ at the mechanic who did the core and motors.
Been reset several times and I see 0 movement at the door driver up above the gas pedal nor do I hear any "door movement" on the system when changing from defrost to floor etc. Please any ideas Id be grateful for. My wife is freezing when we have to go anywhere in the thing.
 

· SilveradoSierra Guru
2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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3,172 Posts
If you've done the obvious, made sure the hvac fuses are good, and replaced the actuator, and hvac head unit, then the problem is more work to solve:
-remove the actuator and make sure the two flaps it controls can move easily, and that the cam also rotates easily and moves both flaps. If they don't move easily or stick, that may be a tear apart the dash problem.
-w the actuator removed look at it (plugged in) while you change the mode between defrost, floor and vents. For my '04, it will rotate appropriately. If yours doesn't rotate, you have to diagnose why, could be you got a bad actuator, or HVAC head unit, or a wiring problem. Most likely, this is what is happening, and there is no magic, easy fix.
 

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Discussion Starter · #13 ·
Frankly I lost faith in the shop who did the repairs to make it right, so I decided to have a closer look. Problem #1. I pulled the passenger side lower motor that controls the hot air door and found they installed a 3 pin motor, on the trucks factory 5 wire plug. I assume that is why I could not shut off the heat. Any thoughts on that one? I realize the core replacement is a PITA, but I'm pretty pissed I wasted $1500 and now I'm controlling things by hand after I yanked the motors. Not to mention I was invoiced about 3 times what their worth.
 

· SilveradoSierra Guru
2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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buy the right parts? rockauto has them for decent prices, and if you buy from there, don't forget to use their 5% off discount code.

The other things I would suggest are subscription to the full service manual and a tech ii code reader or mdi obd-usb adapter and tech2win for figuring out what's going on with your truck.
 

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Discussion Starter · #15 ·
I was curious about the code reader bit. As far as obdII codes I have nothing and I have a code reader for that but is it possible to tap into another place for hvac codes or??
 

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Discussion Starter · #16 ·
The shop that did the work replaced 3 motors with GM or AC delco parts. When I looked it was pretty unclear as to which one goes where by description. Is it a case of 3 wire or 5 wire only?
 

· SilveradoSierra Guru
2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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3,172 Posts
IDK the specifics of your model, as I've only worked on an '04, and the electric setups are different between the two trucks. I haven't delved into the wiring details, as I haven't needed to, as just swapping the actuators made the system work again.

If the hvac system does have codes (I'm not 100% sure of which parts of it does), you need a pretty advanced code reader to get them, as basic, cheap ones, just read engine codes. The code readers I mentioned are units that would be used at a GM dealership to help diagnose problems with your truck.
 
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