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97-99 vacuum systems

2K views 14 replies 2 participants last post by  punisher1130 
#1 ·
Ok I am really getting annoyed with this vacuum system for the a/c. Any time I drive on the turnpike ( 65-70mph) my blend doors shut and blow everything out through the defrost vents. I have replaced the vacuum box under the wiper shroud and I don't seem to be able to find any leaks under the hood. Has anyone dealt with and fixed this problem?
 
#6 ·
Ok I found it, it was wrapped in felt tap so it blended in with the hose, not sure if the was from the dealer or one of the many hack fixes the original owner did to the truck. I got it unwrapped, pulled it out and found a small hole in the side of the housing, bet that would be the problem, I am gonna go get a new one and throw it in, fingers crossed this damn thing has been bothering me the whole time I have had this truck.
 
#9 ·
Haven't tried a hand vacuum pump yet but I have gone through the whole system short of the control box under the dash. I took the controls out from the dash and inspected the vacuum hub behind it and it looks to be in good shape, am I missing any components other than the lines to check?
 
#13 ·
That's what I'm going to do, I plan on going to AutoZone and renting one with a gauge since the vacuum pump I have is air driven and does not have a gauge. Not looking forward to getting under the dash though, I always hated working under the dash of any vehicle.
 
#14 ·
Ok I know its been over a month since I last commented on this, life got in the way, but I was finally able to test the system and come to find out that there is actually 2 of those check valves, the other one is a bit hidden. Once I removed the 2nd valve from the line I used my finger to plug the hole then used the manual vacuum pump to draw vacuum and everything held even when I moved my finger around on the hold the needle never moved, I swapped the newly found valve with the one I already replaced and notice a much faster response on the blend doors so I left everything in place, I may loose my cruse control but at least I'll have my a/c.
 
#15 ·
Update: I got the new check valve in and it did help but I'm still having issues, I still need to play with the switch to get it right, but this time when it happened the motor was under load going over a bridge. I am starting to wonder if the plenum gasket it shot again and that is causing issue as well.
 
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