HVAC Fan

I just purchased my 1998 Pontiac Trans Sport. We have owned it 6 weeks and took it on a trip from Vancouver, BC, Canada to Pheonix and back last week.

Up in the mountains (frost at night) the window slowly frosted over even thought the fan was on high?!

Long story short, sometimes the air just doesn't get out the vents. I can hear the fan blowing at all speeds, but no air comes out and then all of a sudden it works? So it's a sporatic problem.

I have tried to fin schematices of the housing to see what I can/cannot fix, but I can't find anything.

Ideas?

Love the van, but defrost has to work consistently in Canada.

Up in the mountains, you need more throttle because of lower atmospheric pressure and then there is less differential between manifold vacuum and outside pressure, which might be less than what is needed to activate vacuum actuators against spring return to "floor", or even to completely closed position depending on design. Even at standard altitudes, keeping the throttle wide open for a while empties the vacuum reserve and all vacuum actuators release to unenergized position. NOrmally, letting the throttle up for a few seconds reloads the vacuum reserve and reactivates actuators..but only for a limited time if hard throttle resumes...but at altitude, it might not be enough.
...
....but, although there is no surprise in what you said, it is possible that , in addition, a leak has developped somewhere and you do not get all the vacuum that you are entitled to...

Thanks,

It makes the trouble shooting I did in the driveway more logical. I tried to manipulate the fan direction Def, Foot, etc, but same results I discussed earlier. Fan ran, but did not seem to come out anywhere.

I gave up trouble shooting the problem and started the van to put it back in the car port. Low and behold the damper changed position. (You have to realize I come from a long history of 1970/80 FS Station wagons. We just broke into the modern era ... haha ... with a 6 year old van)

Seems odd that the damper would fail to a position that does allow any air flow?

Is there an easy way to trouble shoot a vaccuum leak like this?

Does anyone know where I can find drawings/schematics of the HVAC system and the damper controls?

Indeed you realize that the engine has to run for the actuators to operate. No vacuum, no motion, except the warm/cold diverter that has electric positionner. Diagrams I have are for 93 model which terminated with the 96 model year. I have no idea for 97 and beyond.

l8r,

There are some pretty good diagrams here:

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1b/e9/79/0900823d801be979.jsp

Take Care,

Greg A.

Pics look good. Now I need to decide if I am stupid enough to take this all apart for a sporatic problem or wait until it complete fails completely so at least I know whats broke. :)

Thanks,