2nd Gen Non-Engine/Transmission Questions about vacuum readings

[4570]

I bought my truck when it was about three years old used . Almost from the start after a run down the freeway and then parking it in my driveway ,then turning the engine off ,I could hear a hissing noise from under the hood .By the time I got the hood open it would stop so I never did find what it was but it wasn't the radiator .Now these last 6 months or so my cruise control has been acting up and you had to baby it to get it to set and hold speed on flat roads and any up hill at all would cause it to loose speed when set .I did a vacuum test on the brake booster and it holds vacuum just fine and the vacuum pump at idle is very strong at about 70 inches .I then put vacuum to the cruise control and it leaked as I suspected .I pulled the battery and the unit and the vacuum line was hard and cracked and one spot under the battery looked like it was melted but nothing is hot under there .I replaced the line and now the cruise works as new .There is a vacuum line going into the dash on the side right where the air conditioner lines go in and that line wont hold any vacuum at all .My question is ,is it supposed to? The air and registers seem to still work ok and the lines running into the dash on the drivers side all hold vacuum ok. So what is that line running into the dash with the air conditioning lines and is it supposed to hold vacuum ? Arnie

 

[JR]

I just went out and looked at my truck because I was not sure which line you were talking about. There is indeed a line going into the firewall between the a/c lines. I don't know what it goes to but the only vacuum controlled parts in the dash I'm aware of is the vent controls. When you switch from defrost to vent and the lower vents switch as they should? That line comes off the main header that runs along the firewall so you are losing vacuum, I would at least plug it and see what all works/doesn't work.

 

[4570]

JR ,yes I am going to plug it off Saturday morning when I go out to the shooting range and see what doesn't work. Its about a 40 miles one way trip so I have plenty of time to check operation of the defroster and floor vents and also the air to see whats going on .Im thinking of removing the glove box and see if I can get to that line and see where it goes .Hate the thought of having to remove the whole unit under there just for a vacuum line .