DON TX

I have a 1996 Laredo GC. The vent duct door won't change to the dash vents. It's stuck in the defrost vent position. The hose from the engine compartment to the heater core entry thru the firewall is broken and brittle. I tried tying in there but no go. It must be broken on the other side of the f/w. I removed the glove box & trim but can't get to the vacuum pump that opens to the dash position. Where is the pump I need to get to? How far do I have to get into? Thanks for any responses.

Killabrew

Check your vacuum lines from the vacuum canister located behind the bumper on the right front. Trace your line back to where it enters the firewall. Chances are you will find your line breach.

DON TX

I found the main hose going under the battery tray and can't see anything under the wheel well. I'll dig further tomorrow. When I tied into the hose thru the f/w it felt real loose. That's why I think the prob is there. Thanks.
Don

jnicewan

The hose you cant see goes to a vacuum canster directly under the battery tray, it dead ends at that canister and its purpose is a to store vacuum to maintain speed control and a/c controls during heavy throttle. If you suspected a problem here just pinch the line off for testing. The line going through the firewall goes directly to the control head, so it might be easy to start there and check for vacuum and work your way back.

Just check the line under the hood first, its all easy to get to. It starts at the intake manifold, and it goes across the back to a tee for the A/C controls and then over to the speed control servo and tee's to the vacuum canister under the battery. The line is almost all hard plastic and could have a break or crack anywhere. Mine had a couple cracks over by the speed control servo and one right where the tee is for the line going through the firewall.

Auto parts stores sell vac line that you can use to splice the hard plastic line, its basically the smallest vac line they sell. This line should fit pretty tight and little shot of wd-40 will help slide the rubber line on. I have splice mine in 3 different spots and add a missing check valve too. All of the line under the hood should have vacuum on it with the engine running, including the black line going through the firewall and all the way to the control head.

DON TX

I closed off the hose and didn't get any reaction at the dash vents. Does the hose thru the firewall go to another vacuum reservoir or t off to the other vac motors under the dash? Can I route another hose to t off to the other vac motors? TIA
Don

jnicewan

The hose going through the firewall goes to the A/C control head selector switch. The selector switch then directs vacuum to other lines and then vacuum motors depending on what selection you have selected. You might have a broken, disconnected or pinched line somewhere behind the dash.

Just try to verify that the black vacuum line under the hood is not cracked or broken anywhere else, with the engines heat and vibration and stuff, this line is the most common to fail. You should always have vacuum on the black line when the engine is running.

DON TX

There is vacuum on the supply side in the engine compartment. I've tried sucking on the line into the f/w and can't keep a vacuum there so I'm pretty sure it's where the prob is. How many vacuum motors are in the dash? I've found 2. Lower heater vent and fresh air/recirculation door vent. Could I slide a hose over the hose into the f/w to the next connection to maybe patch the f/w hose? I know my chances are slim, but I really don't want to take any more of the dash out than I have already. I'm down to the support frame and ducting. Thanks for the replies.
Don

jnicewan

If I can remember correctly, there are 2 vacuum motors on the drivers side of the case, or near the accel pedal. One down low and one above that. Sounds like you found the lower one on the left and the recirc one on the right. The upper one on the left might be a little tough to locate, I just cant remember.

I dont understand where you are with finding the vacuum problem. Have you checked the black line at the selector switch for vacuum yet. This could be a simple problem like a broken selector switch. Do you have a vacuum pump for testing? Anyway if you had a vacuum pump you could just unplug the selector switch and check vacuum there, and apply vacuum to the vacuum motors and test for leaks.

Below: If this helps, here are the vac lines, colors and which line has vac on which pos.

Black line = always has vacuum from engine
Recirculation mode = red line has vac (also in off pos)
Panel/Vent mode = green line has vac
Floor mode = brown and yellow has vac
Panel/Floor = green and brown
Def/Floor = brown
Def = none

DON TX

The line I found cracked and broken is the line that come off the vacuum supply from engine and Ts off to the f/w where the a/c lines go in to the f/w. The old hard plastic line they used thru the f/w broke off @ 2 in from the f/w. I patched in there to the T with no luck. There is vac at that T which continues on to the reservoir, cruise control and some where else, I think. Cruise control works and I can feel vac at the broken T to the engine. It must be the main vac supply because nothing moves or changes when I turn the control ****.
I removed the vent control panel today and found there is many vac hoses hooked there. I appreciate the color code. All the hoses are the soft so I'm thinking there must be a junction where the hard line connects. Maybe I can find a trick there. I do appreciate the conversation.
Don
PS...After routing a temp hose from engine vacuum line to back of selector switch and got all positions to work, slow but they work. So all I have to do is reroute a line thru the f/w to the back of the switch. Yehaa!! I'll let ya'll know how it turns out. Now, to look for a weak spot in the f/w. It may not seem like it but you've been a great help. Thanks again.
Don

jnicewan

Sometimes it could be easier or more economical at least to "overlay" a vacuum line for a repair. I have done this before for not only a vacuum line but for electrical circuits. Sounds like it may be easier to splice a new vacuum line to the A/C control head rather than find and fix the old one.

DON TX

I drilled a hole near the accelerator cable where it comes thru the f/w. It should speed up the transition since the temp hose wasn't sealed well. Now, if I can get the rear main seal fixed. Got a guy that says he'll replace it for 125$. Sounds cheap but my Dad says he works on cars all the time. We'll see.
Don

DON TX

I got it all back together today and it works great. Ran another line from the engine vacuum supply line thru the f/w to the supply side of the switch and got all positions. The glove box had been removed when I bought it. The latch had the pivot arm broken and I fashioned a piece of aluminum to replace it and it works like a charm. So far so good. Thanks for all the help. I'm sure I'll be back.
Don