I just had the A/C compressor replaced on my 1993 Taurus GL (3.0L). A
week later, we noticed that the A/C vents in the car would close when
the car was put under medium acceleration. At idle, or once the car
was up to speed, the vents would open up and the interior would get
cold as desired. I know that the vents are vacuum controlled, so I
suspected some kind of vacuum leak caused by a hose that was left off
or possibly cracked during the compressor job. I swore it was
something that the mechanics had screwed up (but it wasn't - read on).
Today I pulled off the engine manifold vacuum port hoses. These two
hoses are at the intake manifold vacuum port, and are about 1/2 inch
diameter hose (normal stuff so far). I plugged one on the hoses, then
did a little suck job on the open hose. After a little acrobatic
positioning, I was able to hear the vacuum leak on a little 1/8 inch
line that runs into the firewall, right where the heater core hoses
pass into the firewall. I spliced that 1/8" line and the vent problem
was solved. Nothing too exciting there. But there's more . . .
The 1/8 inch hose that I spliced, runs from the center of the firewall
(where it passes into the dash), over to the passenger side (USA car).
Just about in front of the passenger, below where the hood hinge is,
there is a little 2"X2" plastic box bolted to the firewall. That 1/8"
line connects to that box. Also, both the 1/2" manifold vacuum supply
lines also run directly to that box. There are a couple other "output"
vacuum ports coming off that box that supply vacuum to the normal
vacuum manifold that's in front of the driver (for power breaks,
pollution control, etc.).
Now what I think is odd is that this little black plastic box in front
if the passenger, also has an input port coming from the (electric)
windshield washer pump outlet. Then there's a water outlet port that
goes (as expected), to the windshield washer sprayer nozzles. Here's
what is interesting: When I spliced the little 1/8" cracked vacuum
line that feeds the A/C vacuum motors, I noticed that there was a
little wetness oozing out around the crack. I put a hose on that 1/8"
line to see if any water would be sucked out (and also to make sure
that my vacuum motors were hold a vacuum). Thankfully, I did not get a
nasty drink, and the dash side off the line held it's vacuum.
This little black box with both water and vacuum lines attached is
technically called a "Vacuum and water distribution manifold". It has
no electrical connections. I have a digram of the box and hose
assembly if anyone would care to take a look. For the life of me, I
cannot figure out why the (electric) windshield pump water should go
anywhere near the car's vacuum system. Does anyone have any thoughts
on this ???
I will greatly appreciate your comments and experience.