|
Back
A/C
Fuse Block Repair for '78-'89 911s
By Steve
Grosekemper
As summer approaches
and the weather heats up, thoughts of long weekend trips in
the 911 will surely pop into your head. Some of these adventures
may actually contain stints of driving in warmer than optimal
temperatures. For these occasions we have the wonderful invention
commonly known as air conditioning. However, nothing is guaranteed
to lower your comfort level more quickly than a failure of
your AC system. This will usually occur about 30 minutes into
a drive, right after you say to yourself, "I think I'll turn
the air down just a tad." The car, as we all know, can read
your mind, and, due to its twisted sense of humor, has just
overheated the A/C fuse block.
The reason this
has occurred is simple. All of the electrical power needed
to operate the A/C system goes through one fuse. This fuse
(#20) is barely up to the task and, as a result, overheats
quite easily. What usually happens is that the fuse ends corrode
with age, and the contacts become weak. This causes extra
heat from the increased resistance and melts the fuse holder
clamping blocks.
Fortunately
the repair and prevention of this problem is not difficult.
The fuse box consists of a line of 21 fuses. These fuses are
divided into 3 separate blocks. The first block of eight fuses
(counting from the front of the car) are for parking, head,
and fog lights. The second block of fuses (a total of 10)
are used for basic electrical functions: sunroof, wipers,
fuel pump, etc. The last 3 fuses, the ones we are interested
in, control the headlight washers, air conditioning,
and power windows. This is called the optional fuse block
for obvious reasons. This is where our repair will take place.
Instructions are
as follows:
1
Disconnect battery ground cable.
2 Draw a diagram of the
wires (numbers and their colors) that connect to the top and
bottom
of this fuse block. This may come in handy if
you run into a wiring question later.
3 Remove these 3 fuses.
4 Loosen all 6 wire clamping
screws, and pull wires just out of their holders.
5 Remove two phillips
head mounting screws and remove the fuse block.
6 With the old block out
of the way, now is the time to repair any wiring that may
have been overheated and might cause a poor connection. In
most cases, you can just cut the offending 1/2 inch piece
of wire off. Then just strip and solder-coat the end and you
will still have sufficient length to reach the clamping screw.
If this is not the
case, a piece of fresh like colored wire can be carefully
grafted into place. This should be a quality solder repair
with heat shrink tubing for insulation, no crimp connectors
and electrical tape!
7 Now that you have fresh
wiring in place, install the new fuse block, making sure the
part number and electrical bridges on the back of the block
are the same as the one you just removed
.( There are different possibilities for different years.)
8 Install the wiring into
the empty wire clamps and tighten the screws. This is where
you might want to refer to your wiring diagram from step #2.
OPTION for step #8 (for 911SCs only) is to split the electrical
load onto two separate fuses. This can be done by attaching
the red and green wire at the bottom of fuse # 20 to the bottom
of fuse # 19. This fuse powers the headlight washers, if your
car is so equipped. This fuse is an excellent choice for load
sharing due to the fact that it is rarely used in conjunction
with the air conditioning, if at all.
9 Reconnect battery ground cable and test operation
of all three electrical circuits. (A/C, power windows, and
headlight washers)
Now, comfort level
intact, all will be well for your next excursion into warm
weather.
P.S. Remember to
change fuses regularly. If the metal strip is wavy, the fuse
needs replacement. Also, be sure to cross reference fuse amp
ratings in your car with the information given in your owner's
manual. If your A/C fuse block shows discoloration, or if
the wire clamping lugs seem loose, now is the time for its
replacement? Not in the middle of your next road trip!
Good Luck!
Appointments
- Ask a Tech - BMW
- Porsche - Detailing
- Directions - Events
- Feedback - History
- Links - Main
-
Message
Board - Order Form -
Parts - PCA
- Products - Quotes
- Staff - Subscriptions
- Warranty
|