2002 S10 HVAC stuck in vent mode.

Boomer

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2002 S10 ZR2 pickup. 4.3 4WD. 123,000 miles. Manual HVAC controls. No CEL and no driveability issues.

I just bought this truck. PO told me "everything works'. I guess technically it works just not correctly. Water pump was leaking. I replaced that. ABS and brake light on. Replaced ABS controller with a salvage yard part and I think that fixed that. HVAC system blows almost all air out of the dash vents only. There is a little at the floor and defrost. This is in all positions. I've searched around and found this thread. http://www.john-stichnoth.com/SonomaT-caseSwitch.html

4WD does seem to work so I'm guessing I don't have all the problems that link showed. What I have done so far. I replaced the 5/32 vacuum line going from the T up by the ABS module to the vacuum reservoir in the drivers side fender. I made sure with a lighted mirror that it was securely plugged in. I replaced the approximately 2 inch 5/32 line on that same T. I replaced the 7/32 line going from the T to the intake. I replaced the transfer case vacuum switch with the upgraded switch. GM part number 89059420. When replacing that, there was only minor evidence of fluid in the lines. I blew the line from the engine compartment going down to the transfer case out with compressed air. I pulled the fill bolt out of the transfer case and nothing came out so, it wasn't overfull. ( I suppose the OP or his mechanic could have drained that down before selling it but, from what I've seen so far, I don't think so)

There is a slight hiss from behind the HVAC controls. I pulled that out and it's coming from the switch that has the multi colored vacuum lines going to it. Absolutely no hint of fluid there anywhere. When I separate the multicolored lines from the black rotating switch, I can take my hand and cover up the holes in the multicolored piece and stop the hiss. This leads me to believe it's the seal inside the rotating switch. That part is not sold separately. I went to the salvage yard and picked up two switches. They both give the same result. I realize they are salvage yard parts so they could be bad too but, 3 switches all bad?? GM wants about $160 for the HVAC controller but, Amazon seems to have them for $60. Before I just shell that out throwing parts at it, Is there a way I can tell?

If I reach up under the dash to the right of the gas pedal to the actuator with the brown and yellow lines going to it and pull the silver arm back with my fingers, the air then goes down to the floor like it should. That's with the switch in floor mode. To me, that rules out a broken door. It must be a vacuum issue. I have to pull pretty firmly on that actuator arm though. Is the vacuum in these systems that powerful?

What would you guys do next? I'm not a mechanic, just a DIY'er. Thanks as always for your time.
 
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#2
Been able to repair several different kinds of these vacuum switches myself for this same $$$ reason. Typical they snap together and can be unsnapped, or use rivets. These I drill out with the proper numbered drill to either tap a hole for a machine screw or use a nut, depending.

Most common scenario is dried up lubricant with that rubber gasket, clean this with denatured alcohol, lubricate with silicone grease and good to go, test these with a hand held vacuum pump. With others, can see small cracks that can be repaired with silicone glue, but this becomes an overnight project as that glue has to dry. Figure I don't have anything to lose as the switch is no good anyway. Especially if the dealer wants you to purchase an entire climate control just for one switch.

Typically can be done quicker than the drive to my dealer and at the end of the month, my CC account is much lower. But you don't know until you try. Same with copper contacts blower motor switches, but have to catch these before the plastic melts. Polished these to a mirror finish with fresh Lubriplate, good for many more years of service.
 

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NickD said:
Been able to repair several different kinds of these vacuum switches myself for this same $$$ reason. Typical they snap together and can be unsnapped, or use rivets. These I drill out with the proper numbered drill to either tap a hole for a machine screw or use a nut, depending.

Most common scenario is dried up lubricant with that rubber gasket, clean this with denatured alcohol, lubricate with silicone grease and good to go, test these with a hand held vacuum pump. With others, can see small cracks that can be repaired with silicone glue, but this becomes an overnight project as that glue has to dry. Figure I don't have anything to lose as the switch is no good anyway. Especially if the dealer wants you to purchase an entire climate control just for one switch.

Typically can be done quicker than the drive to my dealer and at the end of the month, my CC account is much lower. But you don't know until you try. Same with copper contacts blower motor switches, but have to catch these before the plastic melts. Polished these to a mirror finish with fresh Lubriplate, good for many more years of service.
Hey great idea Nick. I will look at one today and see if it looks like it comes apart. I just assumed it wasn't serviceable. I have nothing to lose. Like you said, the switch is no good anyway. I really need to buy me a handheld vacuum pump.
 
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#4
"actuator with the brown and yellow lines going to it" You could remove those lines and test for vacuum with a fingertip. Then rig a rubber hose between actuator and line to give you the ability to pinch the hose for actuator diaphragm diagnosis. If you have a really long hose, you could source vacuum from the engine to test actuator with full vacuum.
 

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Mobile Dan said:
"actuator with the brown and yellow lines going to it" You could remove those lines and test for vacuum with a fingertip. Then rig a rubber hose between actuator and line to give you the ability to pinch the hose for actuator diaphragm diagnosis. If you have a really long hose, you could source vacuum from the engine to test actuator with full vacuum.
Thank you mobile Dan. Do you when each line should be getting vacuum? I guess what I'm asking is, when you select floor mode the yellow line does this and, when you select dash vent, the brown line does this? Being a holiday, I can't go buy a long hose today. I wish I had a known working controller to try but, I don't.


Nick and everyone, I just took the switch apart and cleaned and greased the rubber gasket but, it didn't seem to help. I still have a hiss at the switch and no air control. Any ideas there?
 
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#6
This forum string starts off with "no heat" but then moves on to other concerns... http://www.s10forum.com/forum/f299/no-heat-506612/
 
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Hey Boomer, maybe not in the switch but in the attaching hoses. Another money saving trick is to cut off about a half inch off each hose and jam them back on for a tight fit. Generally a check valve off the intake manifold that feeds a reservoir for even more leaks.

Air should flow toward the intake manifold, can also find deformed hose connections there. Can even find a leaking canister that spot of glue would repair. Certainly not rocket science. Vacuum systems should suck.
 

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Mobile Dan said:
This forum string starts off with "no heat" but then moves on to other concerns... http://www.s10forum.com/forum/f299/no-heat-506612/
nickb2 said:
Dan, is this same op as the other s10? Probably busted something whilst trying to repair. Anyways, there is a link for AC concerns at top of page. :idea:
Not the same OP at all. No relation between those posts. My truck has great heat. I just can't really control where it comes out.
 

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NickD said:
Hey Boomer, maybe not in the switch but in the attaching hoses. Another money saving trick is to cut off about a half inch off each hose and jam them back on for a tight fit. Generally a check valve off the intake manifold that feeds a reservoir for even more leaks.

Air should flow toward the intake manifold, can also find deformed hose connections there. Can even find a leaking canister that spot of glue would repair. Certainly not rocket science. Vacuum systems should suck.
I've replaced the hose going to the intake as well as to the reservoir. Can that multicolored hose attachment be serviced? I don't mind spending a little to fix it, I just don't want to buy parts I don't need. There is a definite hiss at that multicolored hose connection. I suppose it would be there when not connected to the switch but, it's still there even when it is connected.

Would you guys at your shop, replace the whole controller at this point or, do further testing?
 
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#11
Normal default mode for no vacuum is the defrost mode. Sometimes has nothing to do with the MVAC system, found problems with other vehicle with a vacuum leak in either the cruise control or the vacuum parking brake release, all share the same reservoir. Then also can find leaks in the actuators.

I really don't care what color these lines are when I can buy black vacuum line for a round a dime a foot. For that P-30 purchased three bucks worth and replaced every line.

Trying to think of the last time I worked with those multi-color plastic vacuum lines. Poor choice, that plastic gets brittle with age, replaced those with neoprene.
 
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#13

"actuator with the brown and yellow lines going to it"
Looks like the yellow hose should have vac at the #1 position and the brown hose should have vac at the #3, 4, and 5 positions.
 

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NickD said:
Normal default mode for no vacuum is the defrost mode. Sometimes has nothing to do with the MVAC system, found problems with other vehicle with a vacuum leak in either the cruise control or the vacuum parking brake release, all share the same reservoir. Then also can find leaks in the actuators.

I really don't care what color these lines are when I can buy black vacuum line for a round a dime a foot. For that P-30 purchased three bucks worth and replaced every line.

Trying to think of the last time I worked with those multi-color plastic vacuum lines. Poor choice, that plastic gets brittle with age, replaced those with neoprene.
nickb2 said:
if you hear a hiss sound, keep looking and don't throw parts at it. Vacuum leak for sure.
I want to make sure you guys understand what I'm saying. The picture I am going to show is NOT my actual part. It's a picture I found on the net. The hiss is coming from this part.
If I take the palm of my hand and cover the whole face of what you see in the picture, the hiss goes away. I figured since it's unhooked, with the engine running it's bound to hiss. Now it mates together with this part.
Now that is my actual part. I thought maybe that rubber seal was bad but, it looks ok. I put a little silicone grease on it but, it didn't help. That switch isn't sold separately. You have to buy the whole controller. I got two from the junkyard but, same results. Hiss there and air going all over.