99 ram A/C vent problem traced to vacuum leak...

[mahicks3322]

I have a 1999 dodge ram 1500 4x4 5.2l.
I have the "wild vents" syndrome where my vents at throttle switch to defrost.

I have done the following to locate/fix the problem but have some questions to get me further....

1. checked ALL vacuum lines with a vacuum pump. ALL lines hold vacuum except for the very thin vacuum line that goes through the firewall behind the glove box into the heater core housing area. This line holds vacuum for no appreciable time. Line does not seem to be damaged going into the firewall.

2. Installed the ram TSB fix for "wild vents" A 35mm cannister looking check valve/vacuum reservoir at the line before it enters into the firewall.....This helped the problem and allowed me to accelerate mildly before I lost enough vacuum to switch to defrost. It also recovered a little quicker but did not fix the problem anywhere close to acceptable.

3. disconnected the GREEN vacuum line that goes to fresh air door vacuum controlled pump behind the glove box. (it was the only easily accessible vacuum line I could get to. while I can see/feel the vacuum line coming into the firewall from the engine compartment, I cannot get to it easily to trouble shoot it.) I observed the following..
-While my vacuum tester is connected to the green tube with the ignition switch to on but engine not running, AND the defrost/vent switch on max a/c; I get a quick vacuum loss until about 4" of vacuum, then a pretty good hold for about 30 seconds. Then I lose all vacuum and it switches to defrost.
- With the engine running, I get normal vacuum at idle on the green vacuum line under max a/c, but a loss of vacuum on this line on every other switch setting and it goes to defrost.
-switching the defrost/vent switch while the engine is running to different settings seems sluggish but it does switch.



My question are (sorry for so many):
A. should I expect vacuum hold on the line going into the firewall to the climate control system?
B. How can I test the defrost/vent vacuum switch? I tried to pull off one of the colored connectors, but it seemed like I was going to rip the tubing in half so I stopped. Can I unscrew the two nuts on the back of the switch to disconnect the connector and isolate/test each port? If so, what am I looking for? This step is VERY important to me because it keeps me from ripping my dash apart further if necessary.
C. If my testing of the defrost/vent switch turns out that the vacuum problem is somewhere else, where/how do you recommend I look/test?
D. could my problem be corrected by installing another check valve/vacuum reservoir inline or make-shifting my own much larger vacuum reservoir?

Thank you for your help with this issue. I hope my trouble shooting makes it easier for you to give me an accurate diagnosis.

[ocpaul]

I believe that the green line should be under vacuum with the selector switch in the "off" and "recirc" positions. In all other positions it is vented - i.e. NOT under vacuum.