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Mercedes
Benz 107 AC / Heat System Trouble Shooting
Got Heat or AC System Problems ?
Mercedes 107 Heat System / AC Problems and Remedies
There are a number of reasons that the heat system,
air conditioning and climate control fail or just don't
work well on the Mercedes 107 series models, while there
are multiple issues that occur to create these problems,
there are some affordable solutions to their repair and
here are some main reasons and their solutions.
Heat, AC & Climate Control
#1 Climate Control Servo Unit. During the Seventies,
German cars were not noted for their effective air
conditioners, and these SLs are no exception. Except for
the servo units in the automatic climate-control systems
of the 1977-1980 450SLs, which seem to fail every three
years, the air conditioners don't break particularly
often. "They just don't cool well".
Has your 1976 to 1984 Mercedes' Climate Control
System stopped functioning?
For example: when you try to select blower / air
conditioning... is heat all you can get? ...no air? In
fact, no matter how you set the controls... you can't
any-longer actually turn-off the heat? The most likely
problem: Your vehicle has a defective climate control
servo. (To verify your servos' proper function, while
you place your ear as close to the unit as possible so
as to listen to how it reacts when it receives power,
simply have someone turn the
ignition switch (key) to the accessory position.
Immediately as the accessory position is engaged, you
should easily be able to hear a "whirring sound" coming
from within the servo unit - which sound results from
the small motor which powers the unit turning gears
inside of it...like a clock. If no such sound can be
heard: your servo is defective.
 Replacing
the Servo can be expensive...up to $1,200.00 for a new
unit and from $350.00 and up for a rebuilt one. And you
know what? Believe it or not, with the use of a few
simple tools, ( a 3/8" spanner and a screw driver) in
under 1 hour, you yourself can actually easily fix this
problem...That is, you can simply remove your defective
servo and replace it with one that functions.
Important Note: The old servo units are made of
plastic that cracks causing them to fail, look for newer
aluminum body units with a 2 year + warranty, core
charge may apply. One place to get aftermarket aluminum
units is at German
Star for $465.
Servo Replacement Alternative.
1977 to
1980 Climate Control Servo Bypass Conversion Kit For
use to convert 1977 to 1980 automatic climate control
servo to a manual system. If your heat has failed again
and you do not want to spend another $400-600 for a
climate control servo and amplifier maybe it is time to
just convert to a manual system. It will not be as nice
as the original automatic system, but at least you will
have heat when you need it. This kit comes with a new
manual control valve, hose section, splice fitting, four
German hose clamps, a 5 foot control cable and complete
instructions on how to properly install this kit
yourself.
#2 Blower Motor Issues. If your blower motor has been
intermittent or some days it just will not come on until
you drive for a while, or not at all, your motor contact
brushes are most likely at the end of their life. At an
age of 15 years old or more heater motor brushes are
very prone to failing at any time from wear and age.
This is something you may just want to replace as a
preventative measure. If they have not failed yet they
most likely will sometime soon.
Repair Broken Heater Box
Brush
Replacement Guide Order Brushes
#3 Center Vents Don't Open or Stay Open. If you own a
late-model 107 that uses vacuum actuators to operate the
air distribution flaps, then you have probably
experienced loss of function of the center vents (among
other air distribution problems). Reports have been
shared of fixes ranging from "propping open the center
vent" to plugging vacuum lines to allow air circulation
from the vents. While the most common cause for loss of
function may be degraded and failed vacuum pod
diaphram's, other causes do exist and can be more
onerous. The following pages and pictures are offered to
shed some illumination on the subject of "why do my
center vents not open/stay open?"
Vacuum Elements Repair and Replacement
Mercedes Vacuum System Troubleshooting and Repair Basics
SAVE BIG $$$$$$ IN REPAIR AND MAINTENANCE
COSTS!!!
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