Range Rover P38 # 067 - Troubleshooting HEVAC Motors

The blend (and recirculation) motors can be tested using a 9V battery. Apply power to the two wires that power the motor (black wire and brown wire at C1597) and watch if the lever moves. Reverse wires to move it the other way. Do NOT apply 12V power as it could overheat and burn out the motors.

The recirculation flaps are easily monitored by taking out the fans. These have only two wires to the motors and no feedback to the control unit (White/Green and Black/Green for the right side, and White/Red and Black/Red for the left side). Use either the C0791 connector at the HEVAC (in front of C1597) or the connectors near the flaps on each side.

Always disconnect the connectors at the HEVAC control unit before you test using the 9V battery.

Connector 1597 and 0791:
https://drive.google.com/open?id=1284pMDbO8lwY2zZCnXPw0JuEcZeAz9RX

Blend and Distribution Motor wiring:
https://drive.google.com/open?id=1X75zh3mxrkFeyg-EoSjivGoORHHHcCv2

Recirculation Flap Motor wiring:
https://drive.google.com/open?id=1kIBf5A5xWvE3xTDky874mfqNFSPuK66u

Resistance values for left blend motors (between pin 8 and 13): ~8kΩ on HI and ~2.5kΩ on LO. Right blend motor is between pin 7 and 5.
Resistance values for left blend motors (between pin 8 and 14): ~2.5kΩ on HI and ~8kΩ on LO. Right blend motor is between pin 7 and 1.
Note it can vary by ±10%. And anything in between 2.5 and 8kΩ depending on what temperature you set.

Distribution motor resistance varies between 4 and 6.5kΩ (most likely 2.5 and 8kΩ here too but I couldn't get mine to move fully to either end position.

The above are for the feedback circuits (on connector 1597 at the control unit) and not actual value of the motor itself. The blend motors itself measure around 40Ω (I've seen 30 to 70Ω in my cars).

The blower motor regulation voltage can be measured at pin 3 for the left fan (connector 0791 at the control panel) and pin 6 for the right fan.

At lowest fan speed the voltage is approx 10V (9.5 - 10.5V), and at full speed it is approx 4V. If you set the temperature controls to LO the voltage is around 10.5 - 11.5V. At HI temperature the voltage decreases to 0.3 - 0.6V.

A few more good guides on the blend motors:

https://www.rangerovers.net/repairdetails/blendmotor.html

https://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/49913-range-rover-blend-motor-repair-p38-how-guide.html#post403377

https://www.rangerovers.net/repairdetails/#climate2

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