Hey everyone,

I'm a new subscriber but have lurked this site for years. You all are an amazing resource and I want to thank you all for the wealth of knowledge I've gleaned from you all over the years on my 2 Blazers (started with a 96 LS and now have a 00 LT).

I've owned my 2000 Blazer LT 4wd 4.3l for about 8 months. I thought I purchased a pretty straight vehicle but I'm realizing it is a shop queen. The drive train is solid (155k miles and appears to run without issues, no engine codes on the scanner...only real issue was a dead spot on acceleration but I think that was vacuum related and pretty much went away once I located the vacuum reservoir in the drivers fender...I removed the golf tee plug from the hose (and replaced the hose) and got it connected to the resevoir). Afterwards I could still hear intermittent vacuum from around my left knee when driving. I scavanged the vacuum actuators from the local junkyard (I went through all the blazers I could find and now have 1-2 spares for all 4 vacuum actuators). Replaced the 2 on the drivers side and this fixed the leak (the upper one going to defrost had a torn diaphragm). Once I replaced this, my dead spot seemed non-existant (maybe I'm just dreaming this part...I'm not sure vacuum adjusts timing like in my 67-72 Chevy's...but it sure feels like it). Everything was great for about a week. Then the HVAC temperature stopped getting hot. It would get warmer but not above lukewarm. I purchased an Electric or Temperature Actuator (AC Delco 15-72971 or GM 89018365) for the blend door then I removed the entire dash because I found an almost new interior in a 2001 GMC Jimmy Diamond edition at the junk yard...but it was graphite color and my interior was pewter. With the dash out and the wiring harness still in, I went about replacing the electric actuator. At this point I still wasn't 100% sure this was my problem. So, I took the old and new actuators and hooked them up one at a time to the electrical connection. Then I plugged in the Electronic Climate Control (I have an automatic system) and cycled both units through the temperature selector while holding the actuator in my hand. No movement whatsoever on the old unit, but I thought I felt a faint click from inside. Plugged in the new unit and watched it move as I adjusted the temp control. I thought all was good. BUT, then I couldn't get the unit on the shaft of the blend door. Fought it for 2-3 hours then went searching on YouTube. Found the AC Delco video on using jumpers to move the actuator (mine was out of the zone all the way right). I moved the alignment back into the zone (I didn't know about centering it so I simply put it in an area where I could get the unit back on the blend door). Now that it fit, I thought my problems were solved again. Went to work on the dash (the new dash came from a unit that didn't have automatic controls so I had to install the wiring harness from the old dash). Put the whole thing back together and...HVAC just cycles from hot to cold over and over again. So, I did more YouTube and forum searching. Found a post from a Silverado forum explaining the actuator has to be centered (DO NOT RUN THE ACTUATOR PRIOR TO CALIBRATION ON THE UNIT...I'm beginning to see this was my major issue I wish this was written somewhere obvious). So, I pulled the dash again and removed the actuator. I cycled it to the center position of the unit with two pieces of electrical wire and a 9volt battery and replaced it. Same problem as before. Everything seems to work except the blend door. Just cycles constantly from hot to cold and back. Went back to the junkyard today. Got 2 Electronic Climate Control units, 2 ambient temperature sensors and one HVAC Control. Replaced each one separately. Same problem after each. Temperature cycles hot to cold continuously. I believe I fubar'd the brand spanking new electric actuator with my testing (guess I didn't need that $125). Luckily, I kind of assumed that before today's junkyard trip and had a second on order. It arrived just as I wound up my testing of the new junkyard items. So, I'm about to pull the dash for the 3rd time and put the new electric actuator in. What I'm asking your help with is: Are there other things I'm missing like don't apply power to the actuator before it's in place and calibrated? and is there another controller I haven't checked that could be my problem? Although I'm getting pretty good at it, I would prefer not pulling the dash again once I'm done this go round. I think I've touched everything it could be, am I missing anything? And, the blend door is fine....I can rotate the shaft fully with my fingers when the actuator is removed. Heater core appears fine (obviously since it does blow hot and cold...just does it constantly). Is there a relay with the AC that could do this? or could it be the sensor in the middle of the center vents? or the outside temp (it is the auto version so I know it uses sensors the manual doesn't).

Appreciate any advice you all have. And, if you need interior pieces for your Blazer (including seats and a sunroof), I've got quite the collection in both graphite and pewter.

Thanks!

Chad

 

Wow! I'm impressed with you taking off the dash not once, but several times! That is a job I've long hoped to avoid although I've suspected a leak in one of my actuators too.

Regarding the blend door actuator on the computer controlled HVAC systems, if I remember correctly there is an automatic relearn of its position that it must go through when replaced. Have you let it cycle back and forth, shut it off and put it back to on? I'm guessing you have but I thought it best to ask. It might just do it on its own. I'd have to look at my service manual to find the details.

BTW, on my 99 I was able to replace my actuator by going through the glove compartment. It was not easy.

 

Hi Christine!

Thanks for the reply. I used to live in Moscow. Been in Spokane for the last few decades I have now removed the dash 5 times for this little operation. Only twice completely, now I can get it back far enough to reach the actuator in about 20 minutes (I haven't been fully reinstalling it, just putting the gauge cluster in (I removed the headlight, 4wd and wiper controls from the bezel and they are just sitting in the dash for now...and I don't have any of the main bolts in...its sitting on the support pins and the 5 screws into the dash by the defrost and speaker openings)). I've seen the video on going through the glovebox for the actuator and I bought the 2 foot long swivel ratchet from harbor freight, but decided I would rather go the dash route as those screws looked like a major pain to remove. Plus, my pewter dash had a crack in it and I found a graphite one with no cracks at Pull and Save here in Spokane so I figured I'd get 2 birds.

Here is the follow up from my earlier post:

Open up the dash and removed the actuator. Replaced it with the new one I received in the mail today. Went through the calibration and whoopeee!! It stopped cycling. But, when I moved the thermostat through the temp settings, no temp change except for max heat. Recalibrated 3 times with the same issue. Pulled the dash back so I could get my hand on the actuator while the car was running. When the key is turned on, I could feel the actuator move through initial startup calibration, then it goes back to the cold setting. Felt like room temperature (which according to my console was 85 degrees...this is another issue because I put a compressor and had the ac recharged 6 months ago and its not kicking on even though the light is on the ECC...will have to head back to take it back to my ac guys to find out what's up). When I cycle the thermostat hotter one indent at a time (or fast for that matter), the actuator doesn't move off the coldest setting until I hit max heat. Then it cycles up in stages (feels like it moves a quarter of the way hot, pauses for a second and moves another quarter until it reaches max hot temp on the actuator). When I click it back 1 indent (to 82 on the ECC) it goes all the way to the cold side and doesn't move at any setting until I turn it back to max heat. This is in the auto and manual fan settings. All the other buttons for (fresh/recirculate and all the defrost/vent/heat doors) work as they should. I switched out the ECC with a spare and same issue. Also switched out the HVAC controller (the unit that has all the vacuum lines attached under the ECC) and it was also the same. Same with the ambient temperature sensor. So, I'm beginning to think that the HVAC unit is set up to read ambient temp and correlate that to the thermostat. Since my temperature was around 85 degrees, anything except the max setting sends it to the lowest blend door setting until it reads a temperature lower than ambient (max heat overrides the ambient temp so you can defrost windows etc). This is just a guess since all my spares did the same thing. Or, I've got another bad actuator. I simply don't know what the unit's design is...I have all the service manuals and I've read the Auto HVAC section a dozen times, but I don't have the scan tools to run the diagnostics the manual calls for so I can only plug and play. I'll run it to my HVAC guys on Monday and see if they can tell me what's up while they are fixing the ac.

If you want some help changing that actuator, I've got a pretty good handle on all 5. Could probably get your dash out and replace the electric actuator, recirc and vent/heat actuators in a couple hours, the defrost and vent actuators on the drivers side you can do without the dash off (and you would likely have to completely remove it to get to the upper one for defrost anyway. I knew I had a bad one because I could periodically hear a vacuum hiss by my right knee. Sure enough, the upper actuator for the defrost had a tear in the diaphragm. I've got a box full of vacuum actuators (I'm pretty sure I have 1-2 of each of the 4 vacuum actuators...went to Spalding and spent two hours in the yard with one of their guys pulling every one we could find that didn;'t break the tab getting them out). I also have a full set of pewter seats and some interior trim pieces (I pulled them off my truck). Also have a bunch of graphite interior trim pieces. Found 2 close to immaculate interiors in graphite and pulled almost all of it from both. I have a set of leather back seats (I have a leather passenger seat too, but that's going in my truck for the wife...if the heated seat part works) and a complete set of graphite cloth seats. I also purchased a new front carpet and when I get this HVAC stuff solved, I'm going to install the carpet (the rear carpet is already in, I found one that was 99% perfect in one of the Pull and Save cars) and a set of graphite interior and one set of graphite seats (I replaced my sunroof too...the one in my truck had a stripped drive mechanism. I bought one sunroof from Spalding when I was getting actuators and pulled one from Pull and Save when I was getting a graphite headliner. So, I have an extra sunroof too

I'm currently building a shop so this is all happening on the dirt floor or my driveway, but in 3-4 months I should have a workspace that makes this all much easier.

I just read your signature...I think I'm going to need to get some suspension advice from you. Mine needs redone like the HVAC.

Chad

 

Chad,

Wow, small world. I too have spent time at Spaldings and Pull n'Save! I found a pristine rear carpet, also graphite, for my 99 at Pull n'Save. Because they post the VINs I was able to identify before I got there the ones with the correct interior.

Sounds like you have done everything I could suggest for diagnosing the HVAC heater control system. However, what you wrote about how the heater only seemed to put out heat when on the highest setting matches up with what I recently experienced over the last few days after installing a new Champion 4-row radiator. As an additional check to feeling the temperature of the heater hoses to confirm that coolant was flowing through both of them, I thought to turn on the heater while the engine was running and check the temperature. When I did, it felt like I didn't have much heat coming out just like you described. And just like you described, I was in my hot garage where it was at lest 85 degrees. Thus I think you are likely correct about the role of the ambient temperature sensor and that the temperature of the hot air would not feel especially hot when it is already hot in our trucks.

Have you tried testing the heater system very early in the morning when it is cooler? In Moscow, it has been getting down into the high 50's in the early am.

As for suspension work, yes, please ask. However, know that at the moment my suspension has since collapsed. Both the rear leaf springs and front torsion bars have sagged so that the truck now rides pretty close to the stock height. I'm hoping to get them replaced later this summer. I already have the springs and I found NOS torsion bars for my ZW7 suspension on eBay. Before I do that I need to get my little 82 Prelude back on the road.