HVAC Stepper Repair Tutorial
Alfa 164 (series 1)
first published 10/27/2014
Steven Immel
n.b. A tutorial for replacing the
heat valve stepper via center vent
can be found at this link. Although
that tutorial is still valid the
current write-up takes an easier
approach and addresses both
steppers at the same time, also
without dash removal.
This is a collaborative effort that
wouldn’t have been possible
without the assistance of
numerous posters on the subject
on the Alfa Bulletin Board. THANK YOU!
I had to chuckle when Roadtrip recently called stepper repair “the Holy Grail of Alfa
Romeo 164 repair”. How right he is, 23 years after the introduction of the 164 on
American shores we are still searching! Stepper failure and leaky oil-fed timing belt
detensioners were two of the most critical failings of the 164, and no doubt a contributing
factor to the pullout of Alfa from the US market. Symptoms of failed steppers include a
ticking noise coming from the dash, the lack of control of the air flow through the various
vent positions, or loss of temperature control. AlexGS nicely described the sound as
shunch, schunch, schunch, deteriorating to kerlick, kerlick, kerlick, eventually becoming a
rapid clackclack clackclack clackclack. The picture above shows the two stepper
assemblies mounted on a single bracket responsible for the following functions.
heat valve stepper (HVS) — controlling the hot-cold air blending flap
and
air distribution stepper (ADS) — controlling the distribution drum with its five settings for
air venting: front only, front+floor, foor only, floor+windshield, windshield only (defrost).
(A third stepper, controlling the recirculation flap, is seldom a problem on this car and is
not addressed here).
The usual procedure for stepper R/R is a full dash removal (18+ hours) or a partial dash
removal (8+ hours). It’s not a pretty sight, documented by Alfisto Steve and AlexGS on the
Alfa BB. Both procedures have always scared me, too messy, complicated and with many
hidden pitfalls. One of them is accidental damage to the dash and delicate plastic parts
and the possibility that the dash may never be the same again, little creaks that will be
there forever. AlexGS maintains that a full procedure is the only way that you can fully
address the associated issues of HVAC repair, for example, repairing the “sweepers” on the
flaps and drum. I am willing to accept less than perfect sweeper sealing as long as I get
100% stepper functionality. As a few BBers have pointed out, installing a heater core
shutoff is one workaround for a poorly sealing blending flap, this fix also stops a good
amount of “heat soak”.
Many have attempted abbreviated versions of stepper R/R, either by enlarging the access
hole under the glovebox cover (Del), by shifting the evaporator (MCL), or by cutting off the
front portion of the stepper frame (Ries van Kersbergen). It’s the third screw holding the
stepper bracket, deep inside the dash, that is, in Del’s words, “the main bugaboo” in the
rebuild procedure. The two screws closer to the access hole—we’ll call the lower one #1
and the upper one #2— are not the problem. Roadtrip and Steve Alfisto have explored, as
have I, trying to snap out the ADS from the stepper frame by reaching in there. No go, that
puts the stepper at too much an angle and the shaft binds on the white nose cone on the
opposite side of the frame. The forward “foot” of the ADS transmission is too deeply
engaged to allow the unit to come out laterally.
This tutorial follows Ries van Kersbergen’s basic approach—all the work being done from
the inspection hole—but improves on it in several areas and uses no special fabricated
tools. Once the steppers are out a small modification to the frame will allow the
reinstallation of the frame separately, giving us the possibility of tightening screw #3
unobstructed; then comes the reinstallation of the steppers, one at a time, snapping each
in place. For subsequent repairs the steppers can be removed simply by snapping them
out of the frame; removal of the frame will never be required again for stepper R/R.
Ries understood well the need to remove the end of the stepper bracket as it clears a major
obstacle right off the bat, making it possible to insert a medium-sized human hand into
that cramped area, work with screwdrivers, and have enough space to maneuver the entire
stepper bracket out and back in again. Importantly Ries’ procedure can be divided into
sessions without incapacitating the car. Ries developed this procedure over many hours of
trial and error; I am fortunate to have at my disposal, since March of 2009, an intact 164
dash assembly, remains of my retired 1991 164B; it has provided me countless hours for
planning and practicing; reams of Alfa BB posts on the subject were also very valuable.
Brief overview of procedure
- unplugging top half of Q30 connector & pushing lower half out of bracket
- cutting off of flange of Q30 bracket with help of rotary grinder
- removal of cable from HVS
- unclipping HVS from frame, but leaving it loose in the cavity
- removal of hidden screw #3 with off-the-counter 90° carburetor screwdriver
- removal of screws #1 &#2 with same
- pulling out of stepper frame complete with both steppers
- transplant of stepper gears from donor BMW stepper unit
- modification of stepper frame to allow easy reinstallation of ADS
- checking for condition of ADS drum drive key and repairing if necessary
- reassembly; do resistor fix to reduce motor torque
Special Tools / Parts (beyond common mechanic’s tools) :
- Morton 08-0229 90° carburetor screwdriver + 1” phillips #1 bit
- BMV steppers replacements: the gears you need are from the Bosch 0 132 800 001
stepper motor assy (from BMW 1988 - 1994 735i, 735iL, 740i & 750i). BMW Bosch part
ending 005 may also work for us. You can source these on ebay.com (sometimes) but
ebay.de always has plenty of units at very reasonable prices. On the German site the key
word search is: “stellmotor bmw heizung”.
* * * *
Before proceeding we might ask why the steppers wear out, and wear out faster in some
cars, also what causes the drum key of the ADS to fail. The reason for the general wear of
the gears is the torque from the motor—a constant pulsing motion—applied when the
stepper shafts meet a “stop”. It doesn’t matter if the HVAC is on or off, the pulsing of the
motors starts as soon as the ignition key is turned to “ON”. If you remove the steppers
from the bracket, power them on via the Q30 connector, and select max hot or max cold,
or “defrost” or “front vent” you will see that the steppers will actually rotate continuously
360°... in one direction (or the other), one pulse per second, .8° per pulse. But when the
steppers are mounted in the frame, this movement is restricted to a 90° sweep determined
by those “stops” just mentioned, so when the actuator lever of the shaft hits a stop,
“hammering” on the plastic gears occurs, eventually destroying a section of cogs. For the
ADS the abuse occurs in “defrost” (= total CCW) or “front vent” setting (= total CW).
You can eliminate hammering in the ADS by using the 3 vent positions that are in between
“defrost” and “front vent”, namely “front+floor”, “floor”, “floor+windshield”, these are
completely stress-free positions for the ADS stepper gears. Perhaps many people know this
factoid already but I was surprised to discover an interesting programming feature of the
Alfa HVAC that aids in the use of vent selection: pressing a button once moves the drum
to the selected position, but pressing the same button again moves the drum to the
previous setting, whatever that was, like a memory recall. Only the position “floor
+windshield” is different, where the second pressing changes the position of the drum
about 5°, back and forth, like a toggle as you press that button repeatedly. I’m not sure of
the significance of this two-position option, a slight change in floor-to-windshield air
balance? — maybe it’s just my HVAC.
Why the broken drum key on some cars? This is a little bit of a mystery to me because the
stops of the ADS are perfectly in synch with the rotational limits of the drum. The most
probably reason is a poor (weak) design of the hub; also binding may have occurred as the
sealing flaps on the drum have disintegrated. Naturally if you want to save the drum and
get the longest life from the stepper gears, 1) do Ries’ resistor fix, outlined below in STEP
12—it reduces the torque of the motors by about 30% ; 2) use predominantly the three
“inner” vent positions on the HVAC display (“front+floor”, “floor”, “floor+windshield”),
and avoid setting the temperature to MAX hot or MAX cold for extended periods, just
simply leave it to the HVAC to do the temperature blending for you. I keep my temp
setting at 68°, occasionally bumping it up or down a notch. (BTW if you are interested in
tweaking cabin temperatures by fooling the thermistor of the HVAC, investigate this link).
PROCEDURE
STEP 1 (removal of screw #3)
Let’s go directly to the “bugaboo”, screw #3, as once that’s removed you will have no
major obstacles in front of you. Ries made a lever-action screwdriver with bit, with
pulling action to undo this screw and pushing action to tighten, maneuvering with light
and mirror. I’ve experimented with a number of 90° carb screwdrivers and found the
Morton 08-0229 to be able to do the job even without a mirror. You’ll need two lengths
of phillips #1 bits, first a 1” bit to back off the screw half way, then the stock Morton
1/2” bit. (n.b. You’ll need to jam a piece of paper or tape with the standard 1” bit so it
doesn’t fall out of the Morton.
Before you use the Morton be sure to lubricate its drive bushings with oil—mine came dry!
Also I’d recommend that you remove the spring and ball in the handle to get rid of the
clicking effect. You cannot see screw #3 but it’s just behind the firewall; use the hole in
the glovebox—not the main inspection hole—as your point of entry. Position the tool like
the photo shows, near the upper right side of the motor with bit perfectly horizontal (I’ve
marked the shaft of my tool with an “up mark” (on blue handle) and one for insertion
depth (ca. 9-5/8). A light will help you get the tool in the right spot, but from then on you
do it by completely by feel. Another important orientation guide: once you hit the firewall
with the Morton just back off 1/4”, that’s where the screw is located. Be patient fishing for
it, it may take some minutes of searching, you will be able to tell when you have the bit
engaged when the knob of the Morton shows resistance. You will also know when you
have backed off the screw too far with the 1” bit as you won’t be able to get the tool out
(just tighten it a little until you can remove the tool, then continue with the 1/2” bit, until
the screw drops, that noise will be your cue that you have succeeded.
STEP 2 (getting stepper in optimal position)
With the pesky screw out now we can proceed with the whole job. It is advantageous to
to put the the ADS and HVS steppers in optimum positions before we pull them.
turn the ignition key to “ON” (not run),
press “ECON” of HVAC,
press the button “defrost” (this puts the air distribution drum in the optimum CCW position
if viewing the air drum from the open side). The reason you want “defrost” is because the
drum won’t roll accidentally in this position, whereas the opposite position “front vent”,
accidental rolling could occur due to the unbalanced nature of the drum. If your stepper
is so kaputt that it can’t turn the drum, you can manually position it fully CCW later.
Now set temperature to maximum hot, this sets the arm of HVS fully rearward, making it
easier to reach and remove pal nut and actuator cable.
turn key “OFF”
STEP 3 (unplugging Q30)
Disconnect top half of Q30 multi-connector by squeezing the two locking arms and
pulling outwards. Push lower half of connector inwards, out from metal bracket by
simultaneously pressing the top and bottom retainers and pushing connector inwards.
STEP 4 (remove facing edge of stepper frame)
Grind front portion of stepper frame at the bend
using a rotary grinder or dremel. First lay a drop
cloth underneath the work area to catch all the
metal particles and then position your grinder on
the “elbow” of the bracket. Weaken it a bit by
grinding, then just wiggle the bracket back and
forth until it falls off. Any roughness at the cut
can be smoothed out after the stepper frame is
removed.
n.b. On the bottom side of the stepper frame just below the Q30 electrical socket, there
may be a little plastic fan secured by 2 screws (my old 164B had this, my 164S does not).
This is an alternate cabin temperature sensor that U.S. model cars did not use, you can
remove it, permanently, it is in the way.
STEP 5 (disconnecting HVS cable)
Remove pal nut and actuator rod from HVS with a needle nose pliers and/or screw driver.
(If the actuator arm was not “parked” in the rearwards position before you started this
project, you may be able to move the arm by hand unless the gears are totally messed up.
Once the nut and rod are removed pop the transmission out of the frame by pressing
plastic retaining tab and let the HVS lay in the cavity. (please note that the photo below
does not reflect the optimum position of the arm!!)
[ At this point if you are only interested in replacing the HVS, separate the
motor from the transmission and skip to STEP 7. After finishing the gear
replacement it would be advisable to position the arm to the middle of the
transmission per second photo of STEP 9 to line up with the cutout (slot) in
the frame--it will be easier to pop it back into place. ]
STEP 6 (removal of screws #2 and #1):
Continue with the Morton and undo screws #1 & #2, here both screws are a direct hit (use
the 1” or 1/2” bit for screw #2 and the 1” bit for screw #1 since you’ll be coming in at a
slight angle because of the air tube). A drop cloth placed under your work will catch the
screws as they drop, or just hold a magnet nearby.
Once these screws are out the whole assembly can be pulled out through the inspection
hole. Use a delicate jiggling action to unseat the ADS stepper from the air distribution
drum—be be mindful that the drum is fragile.
STEP 7 (swap in replacement gears):
The replacement of the stepper gears can proceed on your workbench. Much of this was
discussed in italcarnut’s important thread. To remove the ADS stepper first pop out the
white nose cone on the shaft side, then release the stepper by presssing the plastic detent
on the rear part of the transmission. After separating the motors from the transmissions,
split the transmissions into their two halves. The AlfaPro manual advises
Using a small, thin flat-bladed screwdriver, gently separate the top and bottom of the
gearbox casing. (First try inserting the screwdriver into each end of the casing and gently
levering. Alternatively try the tiny slots above each lug). Be patient and gentle: careful
not to damage the casing, the plastic is fragile.
Do the same with your replacement BMW transmission. The swap is really easy: simply
substitute the BWV half with gear set for the Alfa. The side with the BMW actuator is not
used, only the side with the gear set. In other words, we are taking the BMW half with
gears and mating it with the Alfa half with arm. After redistributing some of the grease (add
some if you think it is too dry), snap the Alfa/BMW halves together. You’re done.
STEP 8 (re-cut frame):
While the steppers are out of the frame take a moment to do a second cut of the frame as
shown by the black dots (cutting away a little more metal on the HVS end will give you
some more space to work). File off any rough burrs so there is no chance of getting cut
during reinstallation.
Now modify the frame on the
ADS side: exactly where the
foot of the ADS engages take a
flat file and remove the bottom
part of the opening—the same
width as the foot—it will allow
reinstallation by simply
rotating ADS CCW.
So that the ADS can be easily rotated in and out of the frame with minimum binding of the
shaft and nose cone, take a file and grind away about 50% of the plastic centering pins on
the side of the case (marked by arrows in the photo). Take a piece of sandpaper and round
the edges a tiny bit, it will allow the pins to engage in the holes of the frame easier.
STEP 9 (indexing the steppers for reassembling):
As you recall we “parked” the ADS in “defrost” position before removing it. Now we will
temporarily reinstall the the motor and transmission so that it’s in the same position.
First mount the transmission w/o motor into the bracket without nose cone, move the lever
in the position shown below (max CCW); attach the motor. Now remove transmission and
motor as a unit. Pop the nose cone back in. Now the ADS will be correctly orientated to
“defrost” when re-engaged later.
For the HVS all you need to do is position the arm exactly in the middle of its range as
shown below, that way it will easily slip into the cutout of the frame when installed later in
the dash. Both ADS and HVS are otherwise completely self indexing, that is, once the
motor is turned on and hits a stop, it finds its new operational range.
STEP 10 (checking/repairing the drum key):
Before reassembling the ADS in the car take a moment and examine another potential
problem spot: the end of the drum which provides a T-shaped key is sometimes broken.
You will need a light and mirror. Now is the time to fix it, in situ — despite the
inconvenient position (Ries did it!). Even if it is not broken you should at least install a
modified 3/4” ID brass ferrule to reinforce the outside of the housing from breaking in the
future. The off-set cutouts on the ferrule are there to engage into one of the “flats” of the
drum. If the drum drive is broken or missing a part you can repair it. If you are missing
the broken part a product such as JB Weld can be used to “fill in” the void as nicely
documented by Roadtrip.
STEP 11 (reinstallation of frame followed by steppers)
Once the the remedial drum work is complete you can reinstall the bare frame + nose
cone.
Install screws #1 (long bit) and #2 (short or long bit)—it’s best to start screw #1 with your
fingers to be sure its straight. In case you loose a screw note that these are #8-18 pitch,
3/4” long, not the run-of-the-mill #8-14).) Before snugging them up, do screw #3 (long or
short bit) which is now a direct shot with the Morton tool.
Next thread the ADS and HVS into the cavity. However first mount a wire harness—thin
bailing wiring—around the motor of the ADS and snug it up tight enough so it doesn’t slip,
forming a small loop near the wires that you can hold on to. This will serve as a “handle”
and help you to maneuver the ADS into place. The harness will stay.
Next move the ADS into position, it helps to have the shaft pointing at 10 o’clock as you
thread it past the lower air tube. Once the shaft is started into the hole of the drum, get
the foot of the ADS below its anchor point in the frame, the corresponding detent above its
anchor. Then press the shaft fully into the drum— a little giggling, shaking and cajolling
may be necessary, a flat piece of wood can be helpful, pressing on the side. When it’s
fully engaged simply rotate the ADS CCW and snap the detent into its socket (of course
the plastic pins need to seat into the holes of the frame!). You must get the detent to
actually audibly “SNAP” (lock), to do so you need to insert a little wedge in between the
motor and detent. The photos below show “before-snap” and “after-snap” positions of the
detent.
Install the HVS by inserting the arm through the cutout in the frame, insert the foot in its
anchor first, then snap the detent in its anchor. Reattach the actuator rod to the HVS and
the pal nut. To aid in the reattachment of the rod and nut, you can reconnect Q30, turn
ignition key on, HVAC to “ECON” the select max heat to move the arm closer to the
access hole. Use a tie to prevent the Q30 connector from vibrating or getting in the way of
the arm of the HVS.
Step 12 (resistor fix):
Our final task is to do the resistor modification (very important) to reduce the amount of
torque the motor applies to the gears. According to Ries van Kersbergen, the brainchild of
this upgrade, a 33 ohm resistor, one per motor, provides a 3.5 voltage drop and a .12 amp
current to the motor. Here is Ries’ useful schematic, and also the Alfa schematic, showing
where the 2 wires spilt off (in Alfa schematic this occurs at a “twin” Q30 connector
labelled pin #5 and #12, fed by pink wires from the AC controller). Don’t get too focused
on wire colors as there are variations among wiring harnesses; U.S. cars use a single 12pin Q30.
Where to put the resistors? I would recommend the least difficult position, on the wires
that go to reference points #1 and #7 of the 12-pin Q30 connector—“upstream” of the
actual connector—as shown in the bottom photo (these are the wires that split into two
grey wires in the second half of Q30 [#1 goes to HVS and #7 goes to air distribution
stepper].