Hi all,
So a long, long time ago, I posted a thread with a strange problem I couldn't find anywhere else on the internet:
My A/C would work perfectly for 45 minutes or so, then suddenly, air would stop coming out of the vents. It would just stop. The blower would be fine, you could still hear it, no change - but air wouldn't make it out of the vents. Bizarre, and frustrating. I tried everything, I asked dealers, I asked the forums. I got some pointers, some good, some bad, and got to researching, slowly learning about the A/C system.
The thing is, not as much info as you'd think is available about the DIGITAL (CJ2) climate control system for GTPs. It's been a long road, but now I'd like to share what I've learned in general as well as how I FINALLY, a year later, FIXED my original problem.
Let's get started!
This digital climate control unit is the CJ2:
It controls two SEPARATE systems of actuators that accomplish different tasks.
The FIRST of these is a set of TWO electric actuators (no vacuum involved, just electricity), one for the driver's side, one for the passenger's side. The driver and passenger actuators are actually identical and look like this:
These actuators have a single, simple function: they rotate that white piece at the top to select temperature, anywhere from full cold to full hot. This is accomplished because the white piece moves a "blend door" which selects what percentage of outflowing air comes from the "cold" source (cooled by the A/C system) and the "hot" source (heated by the heater core), anywhere from full cold to half and half to full hot.
There are two so that the driver and passenger can set different temperatures in the CJ2 ("dual mode") and each get different temperature air.
These were not my problem, though I replaced them with Dorman 604-106 as the internal gears were cracking and causing them to fail - a common problem. Easy to replace.
Now the fun part: a SECOND system of actuators. These are VACUUM driven. They control VENT SELECTION, i.e. which vent(s) the air flows out of. There are 5 modes: panel, panel/floor, floor, defrost, floor/defrost... and there are FIVE actuators as a result.
Here's how it works: a rigid vacuum line (black) comes of the middle line of the vacuum 'T' atop the supercharger. It travels back toward the firewall, to the left, over the passenger front strut tower, down and forward below the windshield washer fluid tank, and joins a bundle of cables which all travel together through the firewall into the passenger side footwell behind the glove-box.
The vac line splits off from the rest of the cables at this point and enters a "vacuum tank", which looks like this:
This tank contains an internal one-way check valve so that the engine can pull vacuum on it, but it will not release vacuum pressure back toward the engine. The tank thus stores vacuum pressure so that the system continues to function even if vacuum pressure from the engine is momentarily lost - for example, by flooring it or otherwise cruising at high engine load such that vac pressure drops to zero or below (negative vacuum == positive pressure == boost).
Another (purple) vac line connects this tank to the "vacuum-electric heater control module", which looks like this:
The CJ2 sends electric signals to this unit based on what modes you or the automatic system have commanded. The unit contains a series of solenoids which open and close valves to allow the incoming vacuum pressure to continue to any one of 10 outgoing vac lines - 2 for each vacuum actuator. One line opens it, the other closes it.
And that's how it all works! Or should... don't know why GM didn't just go with electric actuators for the vents too. Later models do.
Some of the vac actuators are incredibly difficult to get to. Fortunately, they seem to rarely, if ever, fail. They look like this, in case you're curious:
Now: how I fixed my problem. Well, it turns out what was happening, I think, is that the rigid vac line from the S/C to the vac tank was partially cracked. It does run near the battery and could have gotten ruined that way. BUT it wasn't broken completely - if it were, vent mode selection would not work at all.
It simply provided very little vac pressure - enough to work at idle, where vac is around 20 inHg, but at highway speeds, where vac can be closer to 10 inHg or less, over time the vac tank would deplete its reserve of vac pressure and vac actuators would get stuck in the middle of a mode shift, unable to finish due to insufficient vacuum pressure. This would prevent ANY air from getting out.
Strange, but apparently what happened. I cut away the old vac line, drilled a new hole through the firewall, and ran a new, silicone vac line from the S/C, through the hole, to the vac tank. I also replaced the vac tank and vac-electric module for good measure - brand new ACDelco components are still available for them. Amazon links and part numbers below:
---Blend Door Electric Actuator
Aftermarket replacement recommended as the GM ones have plastic gears that break.
Dorman 604-106
http://www.amazon.com/Dorman-604-106.../dp/B001C6Q7US
---Vacuum Tank
ACDelco 10403762
http://www.amazon.com/ACDelco-104037...dp/B0016IRGE8/
--Vac-Elec Module
ACDelco 15-72182
GM 16171742
http://www.amazon.com/ACDelco-15-721...dp/B000C9CBG0/
Thank you all for reading, for the prior help I received while troubleshooting this issue, and in general for being awesome. Comments, corrections, and suggestions welcome.
-Komrad36
