Do you have annoying clicking (similar to seeking CD player) sound coming from inside of your Toyota dash, sometimes only happening at set heater temperature setting? It could be “indecisive” heater control servo.

Below is how I fixed the noise in a Toyota Ist (hint: it is was a problem with sliding contacts inside of the servo).

To get to the servo (it sits on top of the heater/AC ducting) you need to remove head unit and heater controls. To get to screws in Ist you need to unclip silver trims (not visible):
heater_control_removal_0

The heater control and head unit surround/centre vents is held by couple of screws. After removal of the screws the surround just unclips:
heater_control_removal_1

The heater control is connected via one plug and a corrugated hose (which vents to a thermistor in the heater control unit):
heater_control_removal_2

The servo is located in depth of the dash board:
heater_servo_location_0

The servo is held by 3 screws (it has 4 holes, just to confuse people) and is connected via single plug
heater_servo_location_1

It was very hard to unlatch the levers so I removed it with them in place. The was 1 screw and a plastic washer holding the levers in place:
heater_servo_removed_0

Levers removed:
heater_servo_removed_1

Servo is held together by plastic clips around the perimeter:
heater_servo_repair_0

The problem is due to wear contact springs lose tension:
heater_servo_repair_1

Here are the contacts in greater detail:
heater_servo_contacts_0

Other side:
heater_servo_contacts_1

The fix is to bend contacts up and clean the contact surface from carbon (while trying not to remove too much grease).

To reinstall the servo make sure that the levers sit correctly. Check that the flaps are actuated properly by moving the lever by hand:
heater_servo_levers_0

After reassembly check maximum temperature (should be 50-60 degrees Celsius):
heater_check_high_temp

Check minimum temperature (should be around 8 degrees Celcius, providing that the A/C is working):
heater_check_low_temp

Check set temperature on lower end (in this case 22 degrees Celsius):
heater_check_22c

Check set temperature on higher end (27 degrees Celsius):
heater_check_27c

Note: temperature settings take a while to stabilize.

Success! No more noises!