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Discussion Starter · #1 ·
Hi everyone, well I finally own another GM truck. It's a '95 Suburban K2500 LT with a 454/4L80E, and it appears to have 3.42 gears. Not sure if it's got limited slip yet or not. I literally just took delivery on the thing last night, and drove it 1200 miles home from Mississippi to Pennsylvania. Gotta love these trucks! Was a comfortable ride the whole way back. I got a great deal on the truck. Of course, it does have a few issues to take care of. Most of these are minor things that I've figured out, however there's one issue that I could use some help on.

I'm noticing that the heater doesn't appear to work especially well. At first, I figured this is probably related to the thermostat being stuck open (the coolant gauge was stuck just a bit above the bottom for the whole drive back), however while driving up today, it was actually warm enough to try to turn the heat down from max, and I noticed that the air coming out of the vents didn't change at all! It was still the warm (not hot) temperature. I then checked the rear vents, and those were blowing out cool, and also not changing when I adjusted the temperature control for it.

My guess on this is that, on top of whatever else may be wrong, there's a problem with the blend door. However, I have no idea where this door is or how to access it. Alternately, if this sounds like a different (preferably easier to fix) problem, then I'm certainly open to that. :)

Any help appreciated... thanks!
 

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Commissioner Gordon
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First, make sure the t-stat is working, you should be at 198*. If you are not getting the coolant hot enough, the heater(s) will not work properly. Once the engine temp is normal, then we can go on to the doors, control heat, etc...
 

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Discussion Starter · #3 ·
Believe it or not today on the way to work the thermostat started working right for a bit! The truck got up to operating temp and it was very comfy in the cabin! Didn't check to confirm whether or not the doors were operating.

Then I got onto the highway and the temp started dropping again. :(

I'll do a coolant flush (needs it anyways) and change the thermostat first to get it working properly. I would much rather have the heater stuck in the on position right now! High today is 15F here in PA.

On another note, I've got a '00 VMax. Great bike. :)
 

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Commissioner Gordon
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The almighty V-Max:ro) Too much fun.:D Chackout my garage for some pictures.

Make sure and go back with a stock t-stat (198* I think) and get the engine to normal operating temp, then we can chack the doors. I'm trying to remember if the actuator for the temp door is on top of the airbox, or on the side. I'll look after while and get back to you.
 

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Discussion Starter · #5 ·
A coworker of mine has a '95 K1500 pickup with a 350, and he said he thinks the system operates on vacuum. I think I may have some vacuum leaks anyways, so I'll take a quick poke at that tonight while I'm playing around under the hood.

Also, does anyone know if this uses DexCool or standard green anti-freeze? Don't want to throw in the wrong stuff.
 

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Commissioner Gordon
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There is no vacuum to the doors, it's all electric actuators. The temp door actuator is near the center of the dash on the front side of the case. Kind of behind and down from the ac control head.

Dex-cool
 

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Discussion Starter · #7 ·
Ok, here's the update.

I got the truck back together. New thermostat, a whole ton of Dex-Cool and water (did about a 70/30 combo, especially if there was any water left in the system - I believe the previous owner may have used mostly water). Got the system I believe bled. The rear heat still blows out cold, but the front heat blows out hot. On the drive up from Mississippi, both blew out warm, so I believe there may still be air in the rear system. Is there a way to bleed this?

The temperature control still does not function. All the other functions do work. The fan control works for both, the vent control works for both, and the AC/recirc buttons both work fine, but there is no temperature control - it always blows out full hot. This is the desirable failure mode seeing as it's 5F out here right now, but I'd rather have control. :)

Any places to look?
 

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Commissioner Gordon
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To bleed the cooling system, run the truck with the rad cap off until the thermostat is open and no more bubbles coming from the rad. May need to run it a while because of the long lines for the rear air.

Here is the fun part, the temp door actuator is in a tight place. Pull your glovebox out and look towards the center of the dash you will see something with a UPC code and bunch of numbers (probably even an 'N' on the end), black box kind of thing, that's the actuator you want to check. The best way I can tell you to check it is to put you hand on it and turn your temp knob from hot to cold and see if you can feel it try to move. If it does, then the door is stuck and will either need repairs or if you can take the actuator off and manualy move the door, once you free it, it will probably work fine for a long while. If you don't feel any attempt of movement, the actuator is dead or the ac controlhead is not sending the signal for it to move. '95 did have it's issues with the controlhead, I've replaced very many of them. On the same hand it's not uncommon for an actuator to die and I have seen doors stick, although that's not that common.

Your going to cry when you see where the actuator is.:(
 

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Discussion Starter · #9 ·
My old '97 GMC Sierra C2500 6.5TD/4L80E had a control head failure, but when that happened only the fan speed worked, nothing else did. The annoying part was this was on a very hot day when I was sitting in traffic, so that meant no more AC. :(

Is there a way to test to see if the signal is being sent? Also, if both the front and rear temp controls are not working (which is what I observed when driving back up from Mississippi), is there some common link here? i.e. do both front and rear electronics go through the front control head? If that's the case, that would make me lean towards a failure of the front control head. Another thing is that the AC compressor is not kicking on. I talked to the PO, and he said he didn't observe any of these problems when he last drove the truck (it sat for a month or two before I bought it).

Thanks for the advice, Rttoys, this is very useful for me. :)

Also, I used to be a Jaguar mechanic. I am used to crying when I see where certain components are located. :( I'm used to crying MORE when I know where they're located, but I can't see them!
 

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Commissioner Gordon
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AC not coming on could be the low pressure switch sticking, since it sat for so long. Turn on ac go to the low pressure switch on the acumulator and tap the switch with a screwdriver or some else hard and see if the compressor turns on. If not, then you'll have to look for things like a dead freon charge on the system or other electrical problems.

As far as I can remember, the front and rear controls and systems realy have nothing to do with each other. The temp door not working on the front and rear is just a very odd coinsidence. That one being a '95, it was the first year of that dash style and of course they had their share of problem with the new control head. It could be anything under the sun too, not just a normal failure, but usually if one thing went bad, many things went bad at the same time on those controlheads.

The actuator is pulse width modulated, so to hook up a test light should get you a flicker when moveing the controls. There are many wires going to it though, I can't remember if it needs feedback to keep pulsing (I'll look it up in a little bit). To tell you the truth, I rarely properly diag an actuator. They don't go bad that often, but if I suspect a bad one, I plug in a good one and see if it moves. Not the right way to properly diag it, but it's faster.:eek::
 

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There are three (3) electrically controlled (motorized) doors inside the HVAC box under the dash. One is for the temp control. One is a blend door for the recirculate feature, and the defroster/heater/vent diverter door. GM probably calls them something else in the shop manual so don't hold my terminology as gospel!
A few weeks ago I replaced the temperature blend door actuator on my Dad's 1995 K1500 Suburban. His initial problem was low heat. I replaced the thermostat, which cured that problem but then we discovered that control of the temp was usually resulting in full HOT all the time. I first removed the black plastic duct (diverter manifold) at the front of the transmission hump, where the carpet meets the firewall. It's the plastic piece with square holes to divert heat to your legs. One screw holds it in place. Remove this piece and reach up inside. With the ignition in 'RUN' (engine off), turn the hot/cold selector both ways and see if this door moves. Also try to move it (don't force it too hard) by hand. If it is easy to force by hand or stop it while it's moving, then the electric motor actuator is bad. A good actuator will be difficult if not impossible to move the door by hand. My dads' would move with ease. Just the airflow from the heater was forcing the door closed so FULL HOT air was coming out all the time. The actuator is tough to replace but you won't have to remove the dash. I removed the glove box, ash tray (whole thing, hinges and all) and was able to get to the diverter door. Took me about 2 hours, and now that I've done it I could do it again in half that time.

Also is a cover under the passenger side interior side of the HVAC box, held in place by 6-8 (can't recall the number, but one of them is up against the firewall behind the box and a pain to get at). Remove this cover and you will have access to the heater core. One screw his holding one end of the heater core in place. Remove that, and pull down on the core carefully so you can feel the other doors if need be.

Bought the new part at a NAPA store. All three doors use the same part number motorized actuators.
 

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Discussion Starter · #12 ·
Thanks for the tips everyone. Here's what I've determined.

I removed the glove box as suggested by Rttoys, and when I moved the temp dial the motor tried to move, but couldn't. So, I removed the stepper motor, and then had it move back and forth several times with it removed. Reinstalled, and it now seems to work properly.

The recirc and the flow diverters both appear to be functioning properly.

Chris, this is almost the exact same problem on my K2500 as on your dad's K1500. I first had to replace the thermostat and then it was stuck on full high heat.

The front now appears to be functioning properly. I also determined that there is no freon in the AC system, so it all leaked out. I will have to diagnose this myself first.

The rear HVAC is still blowing out cold all the time, but this may go back to a bleeding issue or something else. I believe the system is completely bled, but I may be incorrect here. Since the front heater is working properly, that is my primary concern - it's cold out here! :)
 

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Commissioner Gordon
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On your rear ac/heat, after the trucks been running a while, go back to the back passenger side where the lines run, and touch the heater lines to see if they are hot. If they are, then it will be in the case (like the front), if not, then it's a coolant issue.
 

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On my Dad's Suburban, the hose that feeds hot coolant to the rear heat exhanger had a fitting that was corroded internally to the point that almost no flow was coming through. This fitting is at the top of the water pump. It threads into the pump housing. There is a quick disconnect at this fitting. We had to replace both the fitting and the formed aluminum line due to a leak at the quick disconnect. That's how we discovered the internal blockage there. Before tearing into it, run the engine up to normal operating temp and see if that line gets hot with coolant. It runs down to the right side under the airbox and down under the firewall, towards the right frame rail, and back to the rear heat exchanger.

Rttoys, are you a Two Wheeled Texans member?
 

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Commissioner Gordon
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Chris N5CWM;1588530; said:
Rttoys, are you a Two Wheeled Texans member?
If that is some ride'n group then, no. I don't do groups. Use to, but it is a long story why I don't anymore. I do have 3 different bikes I ride (check my garage for pictures). Now my ride'n group is me and 2 or 3 others. I am friendly to all bikers, even Harley riders sometimes.:D
 

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Discussion Starter · #16 ·
Well, whatever was wrong with the rear heat fixed itself yesterday. Oddly enough, this coincided with me removing the blend door motor for the front and loosening that up so that it works properly again. I have no idea as to why, but hey I'm not complaining! Anyways, both front and rear HVAC are fully functional now, except for the AC which has no freon in it. My guess is that there probably was some blockage (maybe frozen coolant from the previous owner) and now after running the thing for a while it finally unfroze all of it. No apparrent leaks, though, and that's something I'm very thankful for.

Thanks for the help, guys, this forum is really great! :)

On another note, I'm on my third motorcycle. First was an '84 Kawasaki KZ700 which had a genuine 100,000 miles on the original engine/transmission! Ran great. My second bike was a '97 Suzuki Bandit 1200S. I really loved that bike, but it was uncomfortable for me so I sold it. Now I have a '00 Yamaha V-Max in carbon fiber. It's a gorgeous bike, and extremely comfortable. However that will be up for sale before long. I love motorcycling, but around here it's too dangerous. Sadly, I think it's safer in New York City. :(
 

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Good to hear your heat is working again!

I've been riding since my early teens. Right now I have a 1984 Honda V65 Magna (1100cc V4). I've also owned a 1985 Yamaha FJ1100, '93 Kawasaki ZX-11 D1, and a '99 Kawasaki ZRX1100. I also have a Kawasaki dual sport KLX650 1995 vintage. There are a lot of nice back country roads to ride away from the traffic just minutes from my house, and a lot of dirt roads and trails to explore with the KLX.

Rttoys, I figured since you were in the Houston area maybe you were a TWT member. I don't post much there but it's a good way to keep in touch with the local dual-sport crowd in this area north of Houston.
 

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Commissioner Gordon
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Fordcrusher, glad to hear all is working well. Theoredicly, the front and rear systems are basicly on their own, but hey if it's working then it's all good.:)

I know what you are saying about it being dangerous to ride anymore. It's insane to ride in Houston, but I use to do it everyday a few years ago. Now my route is head out 290 and get out of town, then have fun.

Chris, I ride street only, don't have a dual sport. I do have a couple of 4-wheels to play on when I'm up on the farm or at biker rallies. I use to be involve in many riding groups until one group mostly rode from bar to bar, then getting on the bike and riding a long way home half blitzed. The other groups I rode with were Ducati and Triumph guys. Great guys, realy learned how turn my bike by watching, following and copying them. Then a couple of guys kept inviteing these other 'hot rod' sport bikers (I call them Westheimer boys) that were more into poping wheelies and straight line racing than true curvy road riding. They were dangerous to everyone in the group and we lost alot of good riders because they didn't want to ride with these a-holes. Well, the last 2 rides I did with these guys, one of those 'hot rodders' went down hard on each ride. It could have very well been me on one of them, but someone was looking out for me. That's when I had enough and didn't ride with them again. The egos were running very high with some of them and that's not my idea of a good Sunday ride.
 

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Discussion Starter · #19 ·
When I lived in Indiana, I actually felt quite safe riding my motorcycles. It was a very motorcycle-friendly environment. The KZ700 and the Suzuki Bandit I had were both great fun out there. I really did ride them anywhere, and enjoyed it a ton. I miss the Bandit.

Moving here to Pennsylvania, though, I'm not as secure, even though I live in a less densely populated road. I live on a twisty backroad where people come flying up on a regular basis. It's not busy, but you only need one person coming on the wrong side of the road, which happens. Plus there are tons of puddles and most of the corners are blind. Worse yet, we have a significant deer problem up here. Fewer deer in Indiana, even though I came close to hitting one on a friend's GoldWing 1200 (good brakes!).

The highway is currently under a major construction here, and as part of it the road has a pattern to it that will cause motorcycles to try to wobble. Plus, they don't mark it well. I was going along one day in the left lane, not going very fast, and then I came over a hill and the lane was completely closed off, with cones. I had an F-150 right next to me and the only spot was in front of him, so I had to downshift and gun it. I missed him and a cone by about 6" each. Had I hit either, I doubt I would be here writing this. Actually, I remember the cone being very close to my left toe. I always wear full gear, but not much helps you if an F-150 runs over you. After that, it scared me pretty badly, and I decided maybe I should look for a convertible instead.

Rttoys, you're absolutley right on how a lot of biker groups are frequently dangerous and annoying to ride with. I was fortunate in having a very good group to ride with, they were all good motorcyclists and taught me a good amount. But most of the groups I've seen are the ones who are just dangerous and into doing stupid things that will end up getting themselves killed. It's dangerous enough being out there on 2 wheels, why do anything to make it moreso?
 
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