Actuator Motor Information
Jeep
The actuator motor on the
Grand Cherokee series is a simple two wire DC motor. The motor is
under computer control and is driven forward and backward by reversing
the polarity of the voltage to the motor.
Generally failure of the actuator motor is due to the comupter control
algorithm shutting the motor down after detecting a fault condition in
the HVAC system. If the computer detects a no response or failure
to calibrate condition, it will turn the motor off until the next
calibration cycle.
The motor can be easily tested with a 9V battery and a snap connector
to the battery. You need a fresh battery since the battery just
has enough power to turn the motor and a partially discharged battery
may not give the right results. Touch the wires to the motor
terminals and the motor will turn and reverse when you switch the
wires. Just for fun try holding the motor drive connector from
moving to see the force that the system has to absorb. This is
for a 9V battery...it's stronger for the 12V Auto system.
You can open the motor and check the gears, but this series of motors are very robust and any problem with gears is rare.
The motor in the Wrangler/Cherokee models is a little more complex than
the GC. The motor has an internal variable resistance capability
that is used to detect the position of the blend door and feed
information back to the computer. The motor is used in different
ways depending on the complexity of the system, but all have the same
capability.
The connector to the motor is a six pin fixture. The pins to the
far right of the connector(looking at the bottom of the motor with the
connector at the bottom) are connected directly to the motor and bypass
the electronics embedded in the motor. A 9V battery and snap
connector can be used to check the motor by connecting the wires to the
two end pins. The motor will reverse when you swap the wires.
The pins are hard to touch with a bare wire and a sleeve
connector soldered to the snap connector makes it much easier.
These are included in HeaterTreater kits, or you can find
connectors at Radio Shack.
Ford
Ford actuator motors are all similar, but have different drive axles
with different patterns for connection to the air control doors.
The motor is constructed such that the axle can be configured to
protrude from the top or bottom of the motor casing. On RHD
vehicles, the HVAC system is built with a mirror image transformation
of the engineering design data to construct plastics. The Ford
actuator motors can be "mirror imaged" by reversing the axle and used
in the RHD system without the need to re-design the motor. This
capability is also used on different applications of the motor where
space and orientation of the motor is a limiting factor.
The motors contain some fairly sophisticated electronics that can
detect and position the axle. All have a simple capability to
accept a variable resistance input and position the motor in relation
to the input. Basically the temperature control knob is just a
resistor that changes value when you turn the knob. The motor
detects the resistance and will move when the value changes.
The resistance detection mode is the easiest way to check the
functionality of the motor. You can used a 9V battery and snap
connector to check the operation of the motor. You will need a
fresh battery, not the one that's been in the kitchen drawer since the
mid 90's.
The diagram below shows the pin locations on the motor. The pins
are difficult to connect to with a bare wire, so you will need a sleeve
connector or a lot of patience. Connect the + terminal of the
battery to pin 7 in the diagram and the - terminal to pin 8. This
will cause the motor to move to the center position. It may
already be centered, so don't be surprised if there is no movement.
____|-----------|___
| 1 2 3
4 |
| 5 6 7
8 |
Male connector looking at the motor
Pin 3 is the variable resistance input to the motor. When you
ground this pin, it appears to be high resistance to the motor and it
will turn to one extent of movement. If you touch this pin to the
positive terminal of the battery, it looks like low resistance and the
motor will spin to the opposite extent. Very simple test.
Connect the power and ground to pins 7 and 8. Touch pin 3
to pin7 and it moves one direction. Touch pin 3 to pin 8 and it
moves the other direction. It's best to leave the motor in the
center position for ease of re-installing the motor.
A common fail symptom with these motors is a "clicking" noise coming
from the motor. This noise is usually gears slipping against each
other
and the plastic gears will make a clicking sound each time they slip
against the next gear. These motors are constructed with the
assumption that the axle is always at a 90 degree angle to the motor
casing and has not wobble or movement outside of it's normal position.
When the axle is straight out of the housing, the internal gears
are planar and mesh smoothly. The clicking indicates that the
gears are out of alignment. The picture below shows a typical
motor that has been opened. You can open the casing by gently
prying the connectors loose and opening the case. You can inspect
the gears for any signs of stripped gears. Also note that there
are "blank" areas in the upper right and lower left hand corners of the
motor casing. You can drill holes in these areas and use binding
posts to securely fasten the top and bottom halves of the motor
together.
FIG. 1
You may also hear a clicking noise from the motor attempting to find
it's center position. This is an electronic signal being
generated by the motor controls and is generally a problem with reading
the resistance values from the variable resistance strips molded into
the circuit board. In the picture, you can see this below the fan
gear. There are metallic wipes beneath the fan gear that slide
along the resistance strip. Sometimes cleaning the contacts and
strip will help clear up resistance issues. If this doesn't help,
it's probably time to replace the motor.