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  #1  
Old 11-06-2011, 12:33 PM
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GM style climate control question

I'm investigating Suburbans, the 92 to 99 body style. I test drove on the other day that seemed in good shape but was puzzled by sounds coming from the firewall area under the passenger side of the dash, down by the black contraption that I assume is the blower motor/evaporator box. Although the AC worked fine every now and then varying between several times a minute and every couple of minutes there was some kind of noise like a flap that would open or close with a substantial hissing and banging sound. Sorry, no other way to describe it. Not very loud just enough to be noticable over the sound of the vehicle at speed. I'm guessing that might have something to do with vacum actuation of the air flow in these things. Does anyone have any idea if that might be right or if it could be something else? I assume this is essentially the same system used in all full size GM pickups of that era? If so would replacement of this unit be a problem?

- Peter.

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81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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  #2  
Old 11-06-2011, 12:50 PM
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I don't think it's normal because our 97 'burb makes no such noise. Certainly not to the degree that it sounds abnormal. There's a rather long hiss when you turn off the engine with the AC compressor engaged. It can go on for half a minute. I'm told that's normal.

I have to wonder if it's a vacuum system, though. Our 6.5TD engine vacuum pump serves only the wastegate actuator. Brakes have hydraulic assist. Maybe there's an electric vacuum pump for climate control.

Sixto
87 300D
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  #3  
Old 11-06-2011, 07:03 PM
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yes 88 up chevy pickups us an all electric hvac system.
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  #4  
Old 11-06-2011, 07:54 PM
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So if that's the case then it's likely and electrical issue.?

- Peter.
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81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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  #5  
Old 11-06-2011, 09:36 PM
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Or the flap isn't moving freely.

Sixto
87 300D
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  #6  
Old 11-07-2011, 07:46 PM
Pooka
 
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This sounds like a well known problem with GM and Ford HAVC systems. Where they used to use vac servos to move the blend doors they now use stepper motors. They are easy to install (once you get to them, that is) and take up a lot less room than a servo.

Normally they will make a clicking or thunking sound and on GM's will do it even if the key is off.

There is no repair; the one that is bad just has to be replaced. I think they run about $70 each for parts.

The good news is that it will not get any worse. The bad news is that some of them are very difficult to get to.
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  #7  
Old 11-07-2011, 09:05 PM
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IIRC........ the recirc door is probably the one misbehaving. R/R the glovebox, actuator is on top of the case behind it...........done!
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  #8  
Old 11-07-2011, 10:35 PM
Pooka
 
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Actuator. That was the word i was trying to think of earlier.

You might be able to go to Rock Auto's web site and get a picture of the one you need. The ones I have seen look like big electrical breakers without a switch.
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  #9  
Old 11-08-2011, 09:05 AM
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Very interesting and useful info as usual folks, thanks. I have not bought the vehicle, I'm merely starting to look around at them as there are a plethora of them going dirt cheap in this part of the wolrd. I've never owned one nor driven one so I figured I'd start testing as many as I could to find out what's what. Might be able to pick one up for a few thousand.

- Peter.
__________________
81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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  #10  
Old 11-08-2011, 08:51 PM
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Quote:
Originally Posted by pj67coll View Post
Very interesting and useful info as usual folks, thanks. I have not bought the vehicle, I'm merely starting to look around at them as there are a plethora of them going dirt cheap in this part of the wolrd. I've never owned one nor driven one so I figured I'd start testing as many as I could to find out what's what. Might be able to pick one up for a few thousand.

- Peter.
If I were on the hunt; I would hold out for a low mileage 1995 model. Those were the last year of the TBI set-up, an absolutely bullet-proof engine management system. Very easy to work on and diagnose. Parts for them are cheap as well. The Vortec's from 96 to old body 99 had fuel pump issues, leaking intake gaskets, reaction shell (trans) problems, a/c compressors leaked, pinion brgs failed, also had a healthy appetite for brake linings. Don't get me wrong, they weren't bad trucks, just more problematic than their predecessors.
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  #11  
Old 11-08-2011, 09:11 PM
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Originally Posted by p7fan View Post
If I were on the hunt; I would hold out for a low mileage 1995 model. Those were the last year of the TBI set-up, an absolutely bullet-proof engine management system. Very easy to work on and diagnose. Parts for them are cheap as well. The Vortec's from 96 to old body 99 had fuel pump issues, leaking intake gaskets, reaction shell (trans) problems, a/c compressors leaked, pinion brgs failed, also had a healthy appetite for brake linings. Don't get me wrong, they weren't bad trucks, just more problematic than their predecessors.
I'm aware of the Vortec's gasket issues but I'd not heard of the others you mention. Thanks for the heads up. Reality though is that in my position price and condition are more relevant than specific model year. I do rather like the relative simplicity of the earlier ones compared to the later but I've read that the later engines were the most powerful and marginally more economical, possibly as a result of a better power to weight ratio. Time will tell. As I said there are lots available so I'm going to try and take my time to investigate as many as possible and try to find one that works best.

My reason for wanting one is really only as a secondary vehicle, intended for weekend and family vacation use. So I'm thinking a 2 wheel drive might be preferable as well, both for simplicity and better mpg's. I really can't see any use for a four wheel drive one.

- Peter.
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81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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  #12  
Old 11-08-2011, 09:35 PM
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Quote:
Originally Posted by p7fan View Post
If I were on the hunt; I would hold out for a low mileage 1995 model. Those were the last year of the TBI set-up, an absolutely bullet-proof engine management system. Very easy to work on and diagnose. Parts for them are cheap as well. The Vortec's from 96 to old body 99 had fuel pump issues, leaking intake gaskets, reaction shell (trans) problems, a/c compressors leaked, pinion brgs failed, also had a healthy appetite for brake linings. Don't get me wrong, they weren't bad trucks, just more problematic than their predecessors.
The hissing is most likely the air trying to push past a closed or stuck flapper. I have to go through all the setting a time or two when mine does this.

I have two of this body style beyond 1995. A 96 and a 99. THe 96 has 210k on it still clicking along. THe 99 has 150k. The only problems out of either were intake gaskets every 100k. The 96 was at 86k and 192k. I have replace a fuel pump once on the 96. THe brake about every other year. Brake parts for front run about $150 total. pads and rotors, I can change them in a about an hour. Other than that I have no complaints out of either of them. These are big heavy vehicle that also drink gas at a fair clip but not bad considering the size and wight. I run about 12-13 mpg in town and 17-20mpg on the highway. Both 350ci 4X4 models with a 3.42 rear. If you get a 2wd add about 2-4mpg to those figures.
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  #13  
Old 11-08-2011, 10:11 PM
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My 05's has been flawless. I have 2 zones, the heat will cook you out on the coldest days and the AC will freeze you to death on 100 degree days. The 2 zones are a must IMHO since most women like it somewhat warm so they can adjust their side and not kill you with heat.

GM seems to do this very well.
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  #14  
Old 11-08-2011, 10:35 PM
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Quote:
Originally Posted by Hatterasguy View Post
My 05's has been flawless. I have 2 zones, the heat will cook you out on the coldest days and the AC will freeze you to death on 100 degree days. The 2 zones are a must IMHO since most women like it somewhat warm so they can adjust their side and not kill you with heat.

GM seems to do this very well.
Better would be to move the controls to the driver's side, so the chick of the day can't reach them!
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  #15  
Old 11-09-2011, 09:07 AM
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Quote:
Originally Posted by Hatterasguy View Post
My 05's has been flawless. I have 2 zones, the heat will cook you out on the coldest days and the AC will freeze you to death on 100 degree days. The 2 zones are a must IMHO since most women like it somewhat warm so they can adjust their side and not kill you with heat.

GM seems to do this very well.
How do you find the seats on the 05? I test drove an 01 which I believe is the same body style as the 05 and found it difficult to get comfortable. The seat seemed too "deep" if that makes any sense. Sort of like sinking into a soft wheelbarrow and it took a devil of a long time for me to find a position that I found acceptable. Strangely enough I found the simple 60/40 split bench on the 92 I also tested that day to be the most comfortable of all the seats I tried. One 92, two 99's and an 01.

As for the split climate, that's not really an issue here. It's always on max cold all the time. This is Phoenix after all. You either need maximum cold or nothing at all.

- Peter.

__________________
81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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