air vent

cobram at cobram at
Tue Jul 10 21:55:44 EDT 2007

Archives are fried, so here's a copy of a good post on the subject.  When
the CC system defaults to AC it's almost always the programmer, or more
specifically 2 bad solenoids in the programmer.

From: Paul Meyers <paul.meyers at>
To: quattro at
Date: Tue, 22 Feb 2000 11:12:41 -0500
Subject: Inside the AC programmer solenoid (long)

This post is designed to supplement the excellent Jan '97 post by Igor
Kessel "re:5000 ac programmer solenoids". If you have been wondering how
solenoids actually switch and what are the leakage modes, this is the
for you. You might just as well stop reading now unless you need to read
this to troubleshoot your ac programmer. You can always find this post in
the searchable archives when you need it. That's how I found Igor's. 
The problem: My pearl 88 5KTQ failed to switch the heat from the
outlets to the footwell, leaving my feet cold in the Utah winter. Gary
Lewis, the PO, had the car in Southern California and never noticed the
problem. Following is my journey to solenoid (and programmer) truth. 
Process: Eliminate all the obvious stuff:
1) Replace the hose going to the recirculation door actuator. On an 88
almost always bad. See sjmautotechnik for the instructions. 
2) Replace the connection hose from the main vacuum system check valve in
front of the firewall. This hose is usually hard as a rock. Take care not
break off the plastic stem coming from the valve. While not overly
at about $25, it's a real pain to replace since the tubing going to the
vacuum reservoir is heat-shrunk onto the valve body. Use the good,
OEM hose. It's not cheap, but you don't need much. Put aside some for a
rainy day.
3) Remove the programmer. I like to take out the glove compartment and
associated underdash panels. Extract the programmer per Igor's post. 
4) Test each of the vacuum lines and motor functions for integrity. If
is like mine, your heat modulator motor works fine, controlling the heat
output in response to temperature. If not, use one of the excellent posts
replacing it. Since mine worked fine, we won't discuss it here. 
4a) Replace the interconnecting hoses in the programmer. Remove the soft
plastic piece that mounts the ends of the colored hoses from the
(you use a 10 mm socket for this). Disconnect the hoses leading to the
solenoids (white things with wire wound around them) from the soft
piece's stems.Replace all the hoses. The hose is cheap, using the small,
American size hose available at your local auto zone. It's cheap and easy
do, so why wonder if that's where the leak is? 
4b) Test each of the lines for function. The black hose supplies vacuum
the engine. You can either use engine vacuum or a Mighty Vac (vacuum
pump/gauge combination, about $40 at your local tool store) to create
vacuum. I attached a Might Vac to each line in turn, verifying that each
vacuum motor/line combination held vacuum when isolated from the others.
this point you know that all the vacuum motors work and that none of the
lines leak. The Bently has a detailed description of what each line
and its normal position.
4c) Test the control head and programmer for properfunction. The Bentley
supplies a chart detailing which solenoids are supposed to be open or
during which control situations. By selecting appropriate high or low
temperatures and using the other buttons to direct air flow to the
etc., you can discover that the solenoids are actuating at the right
For this test, I fired up the engine and jumpered the black (vacuum) line
each of the solenoids in turn, verifying that each was indeed working
(supplying vacuum to the motor) at the right time. Thus, I knew that both
the control head and the programmer electricals were working correctly. 
Now the fun begins. I went through this process several times, each time
fixing a potential leak covered in the previous instructions. Each time I
attached the hoses to the 1 (actually 2, but one is covered with a red
doohickey) to 4 manifold/check valve (yes, Virginia, that little disk
actually has a one-way valve built into it), the flap failed to switch
defroster to footwell.
At this point I took Igor's advice and rounded up a spare (suspect, it
hanging down, after all) programmer from my parts car to see if that
the problem. After swapping, I had the same result. I even swapped out
control head for a known good one, with the same result.
At this point, a fundamental question arose. Just how are those solenoids
supposed to work? DO they vent to atmosphere when not switched in? If so,
how could the system work, since there is a single vacuum line connected
several switched-out solenoids at the same time one is switched in? How
could such a system ever develop a vacuum? I concluded that each solenoid
had to have a built-in check valve, so that the switched-in solenoid
develop a vacuum. But every solenoid valve I tested seemed to leak at low
vacuum, only holding a vacuum when large vacuum was applied. What was I
Here comes the good part. This is why you tuned in. I decided to dissect
of the solenoids to see just how it worked. The rectangular piece held in
metal tabs is designed to leak and filter at the same time. Thus, when
valve is switched out, the back does leak. The filter is just a plate
covered with some sort of porous rubber stuff that filters the air. 
The secret, however, is in the front, where the two plastic stems
The center one connects to vacuum, the top connects to the circuit -- the
vacuum motor. To understand what was inside, I carefully cut through the
glue holding the face plate (with the stems) from the body. While cutting
carefully but forcefully pried the two pieces apart. When separated, they
revealed a single moving part inside. The part is a plated steel disk
the size of a dime, with a rubber pip protruding from the center on both
front and back. This was the secret!
Instead of relying on a spring, the good Delco (now Delphi) engineers
on GRAVITY to bring the pip into close enough proximity to the orifice to
not switched in (functioning as a check valve). When pointed in any other
direction, they will leak, especially at low flow rates. 
When switched in, the electromagnet pulls the disk UP, sealing the rear
and opening the path between the inlet and outlet stems. When switched
gravity pulls it back down. Since there's no spring, the disk must move
absolutely freely inside its enclosure.
So, when you test a solenoid for proper functionality, do the following:
1) unsolder the solenoid from the pc card (you don't necessarily have to
this, it's just more definitive). Shake the solenoid briskly up and down.
You should hear a distinct click, moving the disk from one extreme of its
travel to the other (only about a millimeter).
2) Use a small length of hose to suck from the center stem. Of course the
stems must be pointing down. If the solenoid seals on the slightest
you've got yourself a good solenoid (provinding it actually switches -
need to apply voltage to test that).
If you're testing the programmer after working on it or after replacing
solenoids, the only way to test it is to remount it on the firewall so
it hangs vertically again. Any other orientation (such as hanging down by
the multicolored hoses) will yield unreliable results.

With the offending solenoid replaced with a tested good one from the
programmer, the Pearl 88 is happily pumping out heat to my feet. Of
winter is almost over. 

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