Motor Madness - Information On How To Diagnose Actuator Motor Problems
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 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.
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.