I used an inspection mirror and a flashlight to locate the nipple. Only then could I then use my fingers to try to get the hose on the nipple.
A pair of forceps might come in handy. I then had to use the mirror and flash-light to confirm it was on.

Here is an image I found that shows how the vacuum canister is mounted into the fender.


This view is looking towards the rear, drivers side corner of the engine compartment.

 

Might have to look into an inspection mirror or something similar to help out making sure its completely removed before replacement.

 

Update on my Blazer. I got a new GM front axle actuator and n stalled it and it seems to be working in 4-hi. 4-lo is still not working but I think that is a t-case issue.

 

Hey Christine (or anyone else that can help), I got a question for you.

On my 98 Blazer, 2WD 4DR, I have an issue where if I accelerate hard or it drops down a gear to climb a hill, I temporarily lose air flow to the face vents. Now, it's never been a problem for me cause it goes away quickly, but I think today I stumbled upon the answer to the issue: the blend door.

Now, I think people say it's usually a lose vacuum line going into some resevoir near the ABS pump, but I have no idea where that is. (Stupid question, I know...) Where exactly would this be so I can check it?

 

Just to get our terminology correct, the blend door actuator is the thing that adjusts the temperature of the air by blending the amount of air that goes through or by-passes the heater core. The Blend Door Actuator is electronically controlled and consists of a small electric motor that drives a gear. When this fails (often because the large gear splits), it leaves the blend door stuck in one position or another.

However, there is also a "slave door actuator" that is vacuum actuated that controls how much air leaves the heater core path. Check out the diagram for the vacuum hose routing below to see both the slave-door actuator and the blend-door actuator. (The later is labeled "Air Mix Door Sensor and Motor.")

The up-shot is that although the blend door actuator is electronically controlled, I would argue that there still can be problems with the air changing temperature that has its origin with a vacuum leak.

When there is a leak in the underhood hoses, the one-way vacuum valve in the vacuum circuit is not working or if the vacuum reservoir is disconnected or is leaking, then a lack of vacuum supplied by the engine when it is under load, such as accelerating or climbing a hill, the vacuum actuators can start acting funny as some move back to their default, no-vacuum positions.

Regarding the location of the vacuum reservoir, for at least my 1999 and I think later models, the reservoir is tucked into and under the fender above the left front wheel well, aft of the ABS controller,. and between the rear end of the ABS controller and the firewall. (Post #61 from Oct 23 has that picture.) To see the nipple for the hose will require an inspection mirror and a flashlight. It is not uncommon for the hose that goes to it to rot leaving you with little in the way of extra vacuum to actuate the HVAC actuators when the truck is under load.


Auto-climate control HVAC vacuum schematic. The manual climate control is similar in its routing.

 

Some great information regarding the transfer case vacuum switch that can fail and allow excess transmission fluid into the vacuum system. Included is the revised GM switch info -

GMC Sonoma & Chevy S-10 Transfer Case Vacuum Switch

More info on the revised transfer case switch and replacement -

Revised Transfercase Switch

I'll be changing this switch on my Son's 2002 Blazer with the 3 button system...there is some oil in the lines so all vacuum lines will also be replaced.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

GM Tech Bulliten #1350749 - LINK

Document ID# 1350749 2002 Chevrolet S10 Pickup -4WD

HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components) #03-01-38-009 -(Jun 25, 2003)

HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components)
2001-2003 Chevrolet Blazer, S10 2001-2003 GMC Sonoma 2001 GMC Envoy, Jimmy 2001-2003 GMC Jimmy (Export Canada Only) with 4WD and Two-Speed Electric Shift Transfer Case (RPO NP1)

Condition

Some customers may comment that the HVAC mode switch may be inoperative or stuck in the vent mode. After some diagnosis, oil in the HVAC control head and/or vacuum lines may be found.

Cause

When the transmission or transfer case heat up, the oil may expand and find its way into the transfer case vacuum switch. This oil expulsion may cause the vacuum switch seal tofail and allow transfer case oil to be drawn into the HVAC vacuum lines.

Correction

Replace the transfer case vacuum switch. Refer to the Transfer Case Vacuum Switch Replacement procedure in the Transfer Case sub-section of the Service Manual. Also, replace all contaminated parts in the HVAC system.

Parts Information

Part Number Description 15664811 Switch -Transfer Case Vacuum Parts are currently available from GMSPO. (OLD PART NUMBER - USE NEW PART NUMBER BELOW)

Warranty Information

For vehicles repaired under warranty, use: Labor Operation Description Labor Time K4120 Switch, Vacuum Control Transfer Case -Replace 0.6 hr Add Diagnosis Time 0-0.3 hr Add With Skid Plate 0.2 hr Any additional time for replacement of HVAC components must be submitted as Other Labor Hours and requires appropriate authorization.

Since that document was released, the part has been redesigned. The old part was 15664811 and had a green stripe on it. The new part is 89059420 and has a blue stripe on it.

 

did the vacuum line that was rotten a couple not all.. But DO NOT take out the 4 bolts on Driver Side Fender near top, that holds the bracket that holds the vacuum canister tank.. and that lil Bugger took me 5 hrs middle of night, to figure out what and how? I knew the when it happened..lolo..and the vacuum tank NEW is N/A , Any Where.. break it and be a trip to junk yard, then taking out fender liner or fender to get to it.. after taking the ABS Brake Brain Box loose moving it and close by Junk, as I couldn't see the nipple good. and wanted to make dang sure I didn't break it off.. for the short vacuum line replacement..which was $1.00 for that short piece.. that Curiosity cost me a lot of aggravating hours

 

So where do those lines supposed to connect too? A pic would be great cause I have another pump or something close to that area that is missing a bad line as well.

 

Christine, Do you know where we can get this Vacuum canister? Thanks!

 

Junkyard will be your only source.