OT? Chevy question

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Asked this 2 or 3 times in the Chevy 4x4 group with no replies, so thought I'd try it here:
95 small blazer, 4 door, v-6, auto, 4x4... most available factory upgrades..
The heating/AC often decides the temperature settings for us... Can go to cool to hot randomly, or cold to hot, if the AC is on... I'm thinking some kind of vacuum thing or something, but have no real idea what it might be.. Gotta get it fixed before summer or it's going to lose it's place as our daily driver..
Suggestions? (besides getting a dodge, we already have 2)
mac
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On Apr 5, 8:40�pm, mac davis> The heating/AC often decides the temperature settings for us... Can go to cool

Mac
I had this trouble on a Chevy RV chassis. Turned out to be a leaky vacuum hose where it went through the firewall. Real skinny hose and an even smaller hole in the firewall. Reamed out the hole. put in a thick wall gromet and put in a larger hose. Everything was then OK. Determined the leak location using a vacuum gauge. Initially bypassed the suspect hose with a hose patched around the leak site. Took vacuum readings at the vacuum reservoir. A plastic ball about 4" in diameter. Under the hood.
Bob AZ
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Bob... what was the hose connected to?
mac
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A plastic ball about 4" in diameter.

Mac
Hose was connected between the control head and the reservoir. The real problem was started by the hose going through the firewall and chafing on the restricted opening. Tee in a vacuum gauge on a hose to the reservoir.
Bob AZ
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Does this have automatic climate control or do you have manual settings??
Denny
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I'd bet manual. Reads like a door is free to flop back and forth. Wouldn't think he needs heat there. Were it me, I'd be keeping the thing set for cool all the time.
Roy
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I'd almost promise it is 'manual' in that it is not computer controlled, but uses vacuum to activate the various functions including the water valve and the blend door.
In fact, it is probably similar to the one used by Chrysler! <bg>
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It doesn't matter what it's set on, bro.. just seems to randomly change..
You can be going down the road with it set all the way to cold and it will blow warm air all of the sudden, then go to cool.. almost constantly changing..
mac
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Warm but not hot? Maybe the evaporator is freezing up.
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wrote:

'Cuda has a good point. Bro is it hot or is it warm??
Roy
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Maybe, but it does it even with the AC off.... We were in the States last week and just had it on vent, no AC and it would be cool, then pretty warm, then cool again...
mac
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no, it's manual and a pretty standard kind of twist thing, very much like the dodge controller..
mac
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Denny.. the diagram didn't make it, can you email it to me, please?

mac
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On Sat, 05 Apr 2008 19:40:56 -0800, mac davis

Check all the vacuum hoses in the HVAC unit. Does it swtich to defrost from time to time too? If so that may indicate low vacuum.
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Not that I know of, Peter.. just from cool to warm...
if you set it on vent, floor, both, etc., it seems to stay there, just changes temperature a lot..
mac
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On Sun, 06 Apr 2008 15:19:19 -0700, mac davis wrote:

get rid of the junk and drive the Dodge........
OOOOOOOOOOOOOOOOOOOOppppppppppppppppppppppppppssssssssssssssssssssssssssssss
did i say that out loud? <GBMFG>
--
Chris

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On Mon, 07 Apr 2008 01:28:03 +0000, "Christopher D. Thompson"

Oh, but we have to convert them one at a time, carefully. he'll realize that Dodge is better eentually.
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Ah, but the Dodges were before the Blazer... the Dak in 01 and the Ram in 03..
Now, if I could find one of those Ram Chargers or Power Wagons, maybe..
mac
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On Mon, 07 Apr 2008 01:28:03 +0000, "Christopher D. Thompson"

Can't.. we got the Blazer to limit the abuse to the Ram and Dakota on the roads down here... It's the only 4x4 and only the highway is paved..
OTOH, the Dak sure is fun on the runs to the states and back.. *g*
mac
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On Sun, 06 Apr 2008 15:19:19 -0700, mac davis

That case, look at the water valve and control lines.
If it switched to defrost then that signals a total vacuum failure (defrost is the default mode, for safety).
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