I have a 2000 blazer 4x4. The switch that controls where the air/heat comes out has never worked. Stuck on default "dash" position. Last week the blend door stopped working all together THEN it started working again but goes back and forth between hot and cold about every 5 to 10 seconds. It just keeps doing this over and over. I have read so many forums about the blazer and hvacs not working but I haven't ran across this issue. If someone could point me in the right direction as to what part might be causing this I would really appreciate it. I have read over and over again how all of this works but still not clear on this issue.

 

Here are the 2 codes its throwing for this issue B0408 & B0415. About all I can pull up for those codes is its an HVAC issue. Im thinking its either a bad ECC unit or just a bad Blend door actuator. Any ideas?

 

Here is a bit more info on the problem as well. The Rec & fresh lights blink 3 times when pressed and do nothing. The switch on the right that controls where the air comes out does nothing. I have found out that I have a OPT c68 electronic temp control if that helps.

I think I have narrowed my first problem down to the Blend door actuator. So I guess I will change that since there where no comments. BUT will that fix the other things I have listed in this one? Anyone???

 

No one? I must have some kind of rare Blazer malfunction...Door actuator coming in tomorrow. See if that does it.

 

as far as your codes go one is an egr code and other is secondary air pump code. but they both state that it is "B" circuit so my guess is that you have some issue within that circuit. as far as the heat issue I don't really know maybe a thermostat but I have no clue. are you low on coolant or anything out of the ordinary? I'm no mechanic nor do i claim to be just my 2 cents on your situation.

 

Did some more research this morning and found the B codes were
B0408 Temperature control #1 (main/front) circuit malfunction
B0415 Temperature control #1 (main/front) feedback circuit low

All of my fluids are good and temps stay in the correct range. All of the forums I have read stated that it was more than likely the blend door actuator. BUT I can hear mine opening and closing. Thats the problem. It never stops. Its not stuck like a broken gear. Its like it can't find its spot. Goes cold, hot cold hot..on and on. Even does it with just the key on and not running. I will install the actuator tomorrow and see what that does. Kinda sounding like a bad ECC to me now. We will see.

 

The blend door actuator fixed the cold hot back and forth issue. The gear inside was indeed busted. Still cant control where the air comes out though.

 

There is another blend door inside the hvac housing down near the gas pedal, it is known to break often, this shoud have a vacuum actuator that controls it, first thing to do is locate the actutor and linkage down by the gas pedal, operate the direction control with the engine running (needs engine vacuum to operate) and see if the actuator is moving, if the actuator moves both directions its ok, (!!IMPORTANT!! Turn off engine before the next step, dont touch that thing while its moving, if it has enough force to snap the shaft off a blend door it can do the same to your finger!) grab the shaft sticking out of the heater box that the actuator linkage is connected to and see if it feels like its rigidly attached to something inside the box, if it wobbles around the blend door is broken and needs to be replaced. Check that and post back.

I had a 2000 4x4 that had this broken blend door and once i fixed that i also found that fluid from the transfer case had been sucked up into the direction switch because the seal between the trans and transfer case had leaked whiched filled the t-case to the top, the fluid destroyed the rubber seal inside the control ****, also wrecked my front diff vacuum actuator, trans fluid puffs the rubber up and turns it to goo.

Let me know what you find, would be glad to help.

 

Thank you very much for your help. The day after I installed the Blend door actuator I removed the 2 panels under the steering wheel and found the other 2 actuators. Vacuum lines on both were intact and don't appear to be leaking. I grabbed the metal flat rod on the door nearest the top of the dash and pulled it. Its very rigid and hard to pull with the motor running. It changed to defrost as I pulled it. I unplugged the vacuum lines and pulled it again and it was easy to pull but not sloppy. So Im assuming I have good vacuum and everything is intact inside. The electronic climate control switch I have is the C68 option which is all electric. On the back there are no vacuum lines, only a plug with a butt ton of wires hanging from it. When I turn the switch on the ECC to change from vent to defrost or floor, nothing happens. It always stays on vent. I can't hear or see anything trying to happen either. Its just NULL. It will change though if I pull it by hand. I had even thought about putting a heavy zip tie on it for now to keep it on defrost. My a/c doesnt work anyway but in the cool mornings it takes forever to defrost my my windshield. Where would I look for trans fluid? I have read that in other forums but so far after everything I have pulled and checked I haven't found any. Maybe i'm looking in the wrong places? I do appreciate your feedback as this thing has become very frustrating.

 

I forgot the (C68) was all electronic, that control unit may be at fault, but....it is still possible though that its something else, so don't buy a control unit yet, i worked on one of these In a 99 Grand Prix one time and found that the electronic unit actually controls a bank of small solenoids that send vacuum to the different actuators, i'm assuming this may have the same type of set up, the one i worked on had gotten wet and the solenoids were stuck, i was able to carefully disassemble them and get them working again but don't remember much about it.

Ok see the attached picture, I found that on Rockauto in Heat & Air Conditioning under A/C Vacuum Control Valve, chances are, one of those valves has a chunk of something sticking it open or it may be rusted or corroded inside and stuck in the open position, they are very small orifices and very light action valves. The other picture is to help with locating the part, it looks like its somewhere near the center of the dash, i would start by dropping the kick panel on the passenger side and then drop the glovebox out and look around, if you have a center console you may need to remove that too, that picture isnt real good, it will have an electrical plug and vacuum lines hooked to it, find on of your vacuum actuators and follow the lines to solenoids, take it out and if youre a cheapskate like me take it apart and inspect for stuck valves, be careful though, i seem to remember searching for a tiny spring that popped out when i took the first one apart.

Check into that and post back, good luck. If you can, take pics if you find anything interesting in there.