Hey all,
I figure I need at least one actuator for the center outlet, and at least a new line and maybe a new actuator for the "heat/defrost".
"Center outlet duck actuator" and "heat/defrost actuator" is what alldatadiy calls them.

The black/brown serves the Center Outlet and it leaks through the actuator, but the lines are good. As a unit, the actuator and the black/brown lines don't leak.. The blue line serves the Heat/Defrost actuator, and it/they do leak.

What happens if I disable and plug both of these? Looking at parts...junkyard only (and just as old as mine) and what a pain in the butt to get them out...and I'm thinking I'll just give up some comfort to get it back on the road. 240K, and starting to dissolve as these rigs do up here, but it's a good workhorse. Pulls my trailer and boat, and is pretty unstoppable in the snow.
So...what do I do to get floor and defrost heat? That would make me happy enough.

 

Have you isolated it to either the hose or the actuator itself? If not, you may want to do that as you may be able to get away with just replacing a line and having everything work.

As far as just blocking off the port on the HVAC control module, that would work to get around the leaking component(s). It would simply place the heat/defrost door in the defrost position. Everything else in the system would function normally. You would not be able to get air out of the dash vents without the actuator though.

 

Thanks swartlkk,

The #1 (brown) and #4 (black) don't hold a vacuum alone, but are leaking through the diaphragm in the actuator. When I plug either line at the climate control connector, they hold vacuum. That actuator is relatively easy to get at, if I could find a replacement. But what would that get me?

The #2 (blue) line doesn't hold a vacuum at the connector. Could be the line or the actuator. I still don't know exactly where that is and how hard it is to get to. I see some actuators on Ebay for $30 that "might" work there.

I'm thinking that I'd plug the leakers, including the black/brown lines and I'd have floor/defrost left?

 

There are two actuators just to the right of the accelerator pedal. Check that the arm on the upper one is not broken. This one controls the diverter door within the air box for defrost and floor heat; defaults to defrost position.
Have you checked all the small vacuum lines under the hood? Very common for these to split/break and causes all kinds of HVAC problems. Very easy and cheap fix to replace all of these lines. Also check to make sure the vacuum line going to the reservoir within the right front fender is attached. Very difficult to actually see the fitting....done by feel.

 

It looks like the 98' is a little different than the 97'. My 97' doesn't have two actuators near the gas pedal. The "upper mode" actuator is on top of the heater box. The parts houses, and Mitchell diy all showed the 98' layout, but I finally went to AllData and found a diagram that matches my truck.
Maybe someone realized that putting it up there was a big pita if it ever broke, and moved it to a better spot?

Here's how I diagnosed the problem so far.
I checked for engine vacuum at the line going into the firewall and it was good and strong.
I used a vacuum pump to pull a vacuum on the line going into the firewall and it didn't hold.
I took out the climate control panel, took the mode control switch apart so I could test at the connector for all the vacuum lines. That's #6 in the diagram.
The black, brown and blue lines would not hold vacuum, but grey and orange did. Grey is the vacuum source, so it was getting vacuum to the mode switch ok.

I blew smoke into the black port, and it came out the brown port at the connector. When I plugged one of those lines, it would hold a vacuum. That is the actuator near the gas pedal, and it's double acting so the black and brown lines serve either side of it. There is almost certainly a leak in the diaphragm in the actuator.

I don't know if it is the blue line or the actuator on that line that is leaking. I haven't got any view of it yet! Hope to do that today.
I don't have A/C (bad compressor) and just defrost and floor heat would make it useable in the winter...but it would be nice to have the center vents blow warm air sometimes, too.

I've really got a lot of help from people on here when I was first digging into it. Saved me from going down the wrong road several times.

 

Ahhh....yes the '95-'97 models are different than the '98 - '04 years. I had a '95 as my first S10 Blazer and actuator #1 failed, needed replaced. I got to remove the entire dash to do so. What was more surprising at the time was my local Chevy dealer had the actuator in stock and it was only about $20! This was around 2000.

Good luck.

 

Yes indeed. Took me some time to understand the differences...most of the info is for later models, and even those who should "know better", like Mitchells, didn't show the differences.

I really don't want to take off the dash. I can see it when I take the relay cover off the back on the glovebox, and it's only maybe 6-8" away. I'm thinking of cutting an access there.

I hope I'm understanding this right: If I plug black/brown and repair the leak in the blue line and/or the actuator...would I have center vent heat then?
I can get by with defrost and floor heat...but heat out of the center vents would be great.

Thanks for all the help, folks!

 

It looks like even if I do get that actuator out, the only place I might find a "new" one is a junkyard.
If that actuator doesn't cross-reference to anything newer...a junk yard one would be at least 26 years old and I'd expect a high failure rate.
I've set the Blazer aside till I know I can get a new one.
Does anyone have a GM part # for that "upper mode door vacuum actuator" (defroster door) for a 1997 4wd manual climate control system?

Hold the door...the part # is 52470773
Every parts site I visit says it's discontinued.

 

Do a saved search on ebay. A NOS one sold on ebay in Nov. It mat take a while but I have found many an obscure part this way


George

 

The dash has pivots so that it can rotate towards the seats as it does require two people to actually remove it out of the vehicle. Not that it weighs all that much, just awkward due to the length.
The most difficult part is remembering what screw goes where!
Yes it takes time to get all the trim panels out, but not all that bad. I did it all myself until time to lift the dash out...then my wife helped.

It was sure nice to have heat and AC blowing out where it was supposed to!

Of course you have to find that actuator before doing anything.....good luck with that.