Mercedes-Benz Automatic Climate Control System II Configuration guide

of 1 20
Mercedes Automatic Climate Control System II:
Installation Manual and General Information
All rights reserved.

of 2 20
Before Installation:
-My installation took about two hours to complete.
-Ensure that all fuses are in good condition, and not corroded or knocked out of place.
-You’d be surprised how often a faulty fuse causes the whole system to fail.
-Start the car and cycle through every climate control setting. Make sure any of the issues
present in your automobile are not vacuum leaks. If your climate control system is not
functioning properly as a result of vacuum leaks, this will not solve your problem.
-Before working under the hood, ensure the car has had plenty of time to cool. Make
certain the vehicle is in park with the emergency brake on. Also, disconnect the negative
battery cable to prevent any electric shock or shorts.
All rights reserved.

of 3 20
What’s Included
(1) New electronic control unit with five vacuum hoses attached
(1) Heater core “hot water” vacuum valve
(1) Copper tube
(1) 5/8” to 3/4” radiator hose coupler
(2) Hose clamps
(1) 3/4” Diameter radiator hose
(3) Quick-connect cables for servo amplifier bypass
(1) 4-Way vacuum hose connector
(1) 1/8” Vacuum Plug
(4) Plastic cable ties
Helpful/ Necessary Tools
-Phillips screwdriver (multiple sizes and lengths)
-Flat-head screwdriver/ pry tool
-Various pliers (needle-nose, channel locks)
-Socket Set
-Multimeter (optional for testing)
-Gauge to measure vacuum (if the car has a vacuum leak)
All rights reserved.

of 4 20
How it Works
-The purpose of the Mercedes Automatic Climate Control II system is for the car to
regulate the fan speed and heater valve positions to maximize the passenger’s comfort,
based on the inputs from the thumbwheel. In the original design, the a/c compressor is
constantly running and is mixed with varying levels of heat to reach the desired
temperature in the cabin. The amplifier-servo setup receives a certain resistance value
based on the car’s three-sensor chain, and then uses that information to determine
whether it is in heating or cooling mode, and the optimal fan speed to balance the desired
temperature with the actual temperature. Although the original design sounds fantastic in
theory, the servo and amplifier are poorly designed parts purchased from Chrysler, and
simply cannot stand the test of time.
-My modern update kit easily integrates into the existing system to maintain the original
controls, and provide OEM function. The central control unit you are about to install
takes the job of both the amplifier and the servo. It uses a modern electronics system to
analyze that same sensor chain, and make real-time calculations to balance the
temperature and fan speed. The central control unit is made up of three solenoid motors
that are able to open and close vents inside the car and the heater valve based on inputs
from the user, just as the original system did. These solenoid motors are designed for
medical-instruments and should last many, many more years.
All rights reserved.

of 5 20
Plan for Installation
**Ensure the car is off and cold before working! Also, disconnect the battery.**
-Make note of any vacuum issues before installing the update kit.
1) Remove the glove box to gain access to the amplifier-connector.
2) Following the diagram, install three jumper wires across ports on the amplifier-
connector.
3) Disconnect the vacuum block and wiring harnesses from the servo under the hood.
4) Unscrew the servo from the mounts, and then loosen the cooling hoses from the
bottom four ports.
5) Remove the servo from the car and set it aside.
6) Install the copper tube between the return lines.
7) Install the hot water vacuum valve between the auxiliary water pump and heater core.
8) Cut and insert the source vacuum line.
9) Connect the vacuum line to the hot water vacuum valve.
10) Connect the vacuum hoses from the control unit to the vacuum block removed from
the servo.
11) Connect the old servo wiring harness to the new electronic central control unit.
12) Install cable ties to hold the central control unit to the old bracket/ firewall/
appropriate location.
13) Tidy up and reinstall the battery. Then, crank the car and test for functionality.
All rights reserved.

of 6 20
Make Note of any Vacuum Leaks Before Installation
-Make sure you correct any vacuum leaks you are aware of before installing the update
kit, as they will hinder the function of your new kit. If finding and fixing vacuum leaks is
above your comfort level, consider taking your vehicle to a trusted mechanic to have the
vacuum system tested.
-Behind the glovebox, you will find the car’s vacuum switches. These are often the
source of vacuum leaks. You can test for system functionality by bypassing certain
switches if you believe they are leaking. One switch in particular (labelled #14 or #19
depending on the chassis) controls whether the blower motor can come on or not. If your
blower motor only functions on defrost, you likely have a vacuum leak or faulty
vacuum switch. Some folks have installed an electronic toggle switch in place of vacuum
switch #14/ #19 to manually control whether the blower motor can receive power. See
photos in appendix for details of switch on an R107 chassis 380sl. On my first install of
this kit, my 380SL had a faulty vacuum switch #14. I had to bypass the switch.
-The vacuum system is fairly resilient, so you may have luck bypassing/ modifying
certain areas if vacuum leaks prove far too difficult to locate.
-You need at least 6 inHg of vacuum in the system for my kit to function properly.
All rights reserved.

of 7 20
Step #1: Remove the Glovebox
**Please note plastic fasteners on these old cars are brittle and tired. They will break if
you use too much force.
1) Around the perimeter of the glovebox, you will find up to seven two-piece plastic
fasteners. Using a flat-head screw driver, carefully pry the center piece out first, and then
lift up to remove the outer-section of the plastic fastener.
2) Remove the screws holding the glovebox latch in place. Set these parts aside for
reassembly.
3) Gently pry around the edges of the glovebox light. It will pop out, and you can slip it
back through its hole vertically, so it is safely behind the glovebox liner and out of the
way.
4) Once every fastener is fully removed and set aside, grip the edges of the glovebox liner
and work it out of the car. It too is old and liable to crack, so be extremely careful. After
some maneuvering, you will free the glovebox liner to reveal the inside of your dash. Set
the glovebox liner aside for reassembly.
All rights reserved.

of 8 20
Step #2: Bypassing the Amplifier
1) Locate the climate control amplifier. On the R107 chassis,
it is located in the back left of the glovebox cavity (steering
wheel side). For the other models, it is located on the back
right side (fender side).
2) The amplifier is held in by two Phillips head screws. They
can be exceedingly time consuming to remove. Thus, many
people prefer to simply remove the wiring connector and leave the amplifier in place,
which is fine.
3) Slide the wiring connector off the amplifier. Then install the three included jumper
wires to connect pins 1-2, 3-5, and 7-8. Make sure the jumper wires seat fully in
connector ports. See the diagram below:
All rights reserved.

of 9 20
Steps #3, #4, and #5: Pulling the Servo
1) Remove the Phillips head screw in the middle of the vacuum block attached to the top
of the servo. Then slide the vacuum block out of the servo.
2) Slide both wiring connectors off the servo. Set aside for later.
3) Loosen the hose clamps holding the coolant hoses onto each of the four ports on the
bottom of servo (do not remove the hoses yet).
4) Loosen the two bolts holding the servo to the bracket.
5) See the photo below to tag which side of the servo is for “return” and which is the
“source" for the heater core. Be ready to cork or stop the lines quickly after removing
them from the servo. Minimal coolant loss is very important to prevent too much air from
entering the system. Once you are prepared, carefully slip the lines off the servo one at a
time and stop/ cork them.
6) The servo is now free. Disconnect the two vacuum lines on the bottom of the servo
upon removal of the servo. Then, set it in a safe location (it may drip coolant).
All rights reserved.

of 10 20
Steps #6 and #7: Installing the Copper Tube and the
Valve
1) Referring back to the image on page #9, separate the “return” and “source” sides.
2) Quickly pull the stoppers from the two return lines (one at a time), and use the
provided copper pipe to connect the two lines. Make sure the hose clamps (from the
servo) are loosely on the lines in advance, so you can quickly tighten them down and
secure the copper pipe between the return hoses.
3) For the source lines, the hose coming off the auxiliary water pump is 5/8” and the hot
water vacuum valve you will install requires a 3/4” hose on both sides. Thus, I included a
5/8” to 3/4” coupler and a piece of 3/4” hose. Trim and bend the 5/8” coolant hose
already on the auxiliary pump to the proper length and direction (differs slightly
depending on your chassis), to allow the hot water vacuum valve and the hose adapter to
fit between the two lines. Please see the photos for an example from an R107 380sl.
4) Once the 5/8” hose already on the auxiliary pump is the proper length and direction,
install and clamp the 5/8” to 3/4” coupler to the 5/8” hose auxiliary pump hose.
5) Then trim a short piece of the 3/4” hose and attach it to the black side of the hot water
vacuum valve. Using hose clamps, fasten the 3/4” hose on the hot water valve to the 3/4”
side of the 5/8” coupler you previously installed on the auxiliary pump coolant hose.
6) To complete the cooling-system, attach the white side of the hot water valve to the
heater core “in” line. This line is already 3/4” so no conversion is necessary.
All rights reserved.

of 11 20
Steps #6 and #7: Installing the Copper Tube and the
Valve (Photos and Details)
(You will likely loose coolant during this process, which is not optimal, but you will add
coolant to the coolant-tank at the end, so it the system should bleed the limited air out.)
All rights reserved.

of 12 20
Step #8: Control Unit Vacuum Source
1) The dark green vacuum line coming out of the new central control unit will be the kit’s
vacuum source. This must be connected to a constant source of vacuum, for example the
vacuum reservoir line. See steps #2 or #3 for adequate vacuum sources.
2) (for w116 and w123 only) Behind the brake booster, you will find a three-way
connection between a yellow line, black line, and grey line. The black line branching off
the yellow vacuum source line is the best choice here, as it carries vacuum from the
driver’s side to the passenger side (where you will mount the central control unit). Follow
this black line to the passenger side of the car. Then, cut the line and tap into it. The green
line coming out of the new central control unit is preinstalled with a three-way “T” made
up of hoses to tap into any of these lines. The two halves of the cut line will slip into the
two hoses coming out of the green line.
3) (for R107 only) The vacuum reservoir is located in the passenger front fender. Right
by the coolant tank (along the passenger fender), there will be a yellow and grey striped
line entering into the passenger fender. This is a good vacuum source. Cut the line and
attach it to the green source line coming out of the new central control unit. The two
halves of the cut vacuum line will slip into the two hoses coming out of the three-way
“T” on the green vacuum source line.
All rights reserved.

of 13 20
Steps #9 and #10: Vacuum Accessory Connections
1) The white vacuum line coming out of the new central control unit slides onto the
fitting onto of the hot water vacuum valve you previously installed.
2) See the diagram of the connector removed from the servo unit below:
-Push/ connect the blue line from the new central control unit into port #8.
-Push/ connect the clear line from
the new central control unit into port #5.
-Push/ connect the red line from
the new central control unit into port #7.
-Push/ connect the provided 4-way
vacuum line connector into ports 1, 2, 3,
and 4.
-Push/ connect the provided 1/8” vacuum plug into port #6.
3) On the bottom of the servo, you disconnected a yellow (or white) and black vacuum
line previously. Using the provided short piece of 1/8” inside diameter vacuum line, slide
each vacuum line into the hose to attach them together.
All rights reserved.

of 14 20
Steps #9 and #10: Vacuum Accessory Diagram
All rights reserved.

of 15 20
Step #11: Connect the Wiring Harness
1) Locate the two wiring connectors you removed from the servo.
2) Remove the four screws holding the top onto the new central control unit included in
the kit. Identify the 10 harness connector pins at the bottom of the board. From the
perspective of the 10 pins at the bottom of the board (solenoids at the “top”), the pin on
the far left is pin #1 and the pin on the far right is pin #10. Be very careful to identify
which is which pin, you don’t want to install the connectors backwards. The connector
pin groups are also labelled for color on each end of the board.
3) See the diagram on page 16 to identify which of the two Mercedes wiring connectors
goes on each of the two 5-pin groups. Slide each of the respective wiring connectors onto
their 5-pin attachments on the board.
4) Once the two wiring connectors are fastened to the board, route the wires through the
cutout on the lid of the central control unit case before reinstalling the four screws. See
the photos below.
All rights reserved.

of 16 20
Step #11: Connecting the Wiring Harness Diagram
Cable Connectors Board
All rights reserved.

of 17 20
Step #12: Securing the Central Control Unit
1) Once you have attached all vacuum lines (plus double checked your connections) and
fastened the two wiring harnesses to the pins on the board, you are ready to attach the
new central control unit to the servo bracket.
2) Using the plastic cable ties provided, slip them through the holes in the central control
unit case and the holes in the bracket where the servo once mounted.
3) Fasten the cable ties, and ensure the central control is tightly held to the bracket.
4) If you prefer to fasten the central control unit in a different manner, that is completely
acceptable. Please see the attached photo for reference.
All rights reserved.

of 18 20
Step #13: Tidying and Testing
1) Using cable ties provided, organize the vacuum lines and wires in a clean manner.
Make sure there are no vacuum lines in the way of moving parts, or against hot surfaces
(such as the exhaust manifold).
2) Double check the amplifier jumper wires. Make certain you didn’t leave wires exposed
or shorting against a piece of metal inside the dash. If you would like to wrap the
amplifier connector in electrical tape for piece of mind, this is highly recommended.
3) Reverse the steps outlined on page 7 to reinstall the glovebox.
4) Once all wires are neat and orderly, and nothing is left exposed to short, you may
reconnect the battery cables. Follow proper procedure: positive first, then negative.
5) Start the car and perform the following test:
1) Run the engine until the coolant warms to operating temperature.
2) Press the defrost button (DEF). The blower should run at maximum
temperature, and the dash vents should blow hot.
3) Make sure the switch on your panel shows: “Air Cond” On
4) Press “auto high” and slide the wheel all the way to 65 degrees. Allow a couple
minutes for cold air to come out of the center vents. If functioning as designed, the
hot water valve should close and the blower should run at maximum speed. Allow
sufficient time for the interior to cool.
All rights reserved.

of 19 20
Step #13: Tidying and Testing
5) When interior is getting close enough to the desired cold setting, the blower
motor should slow down. When the blower motor slows, raise the dial to 75
degrees. Carefully watching under the hood, you should see the hot water valve
pulsing within a few minutes. Proper pulsing indicates the system is adequately
regulating temperature.
-My fuse blows every time I press auto low or high, what should I do?
-Fuses blowing suggests a defect in the wiring harness. Go back through the wiring
harness both inside the engine bay, and behind the glovebox to ensure there are no shorts.
You want to look for pulled connectors or torn wire-casing.
-The blow motor only comes on when I press DEF, what should I do?
-First make sure power is getting to the central control unit, by checking the wiring
harnesses with a multimeter. Another way to visually observe power getting to the central
control unit is if the hot water valve is pulsing, then it is getting power.
-Second, you need to check your system for a vacuum leak. Make sure there are no
cracked diaphragms or pulled vacuum lines. The issue is almost definitely a vacuum leak.
You can test the hypothesis by disconnecting the connector from vacuum switch #14/ #19
(labelled #14 on R107/ #19 on W116 chassis), and jumping the connector on the wiring
harness to bypass vacuum switch #14/ #19. This vacuum switch
All rights reserved.

of 20 20
Step #13: Tidying and Testing (Continued)
(Blower motor question continued) controls whether or not the blower motor can get
power on non defrost settings. Once you bypass it, so long as the ignition is on, your
blower motor will run. If you cannot possibly find the vacuum leak, you can install a
toggle switch between the wiring harness bypass wire to manually control when the
blower is allowed to receive power or not.
I’m not getting any heat, what should I do?
-Make sure you’ve given the engine plenty enough time to get warm. Then check both
inside the central control unit case (remove the four screws on top) and on top of the hot
water valve to make sure the vacuum lines haven’t slipped off any part of the kit. Contact
me if you need any additional help.
All rights reserved.