If your climate control is giving you issues, the control unit has a self-diagnostics feature, similar to the ECU.

Original writeup from TTZD.com.

Procedure

Entering Diagnostics Mode

autoccnumbered.gif
  1. With the ignition switch turned ON, Press AUTO and OFF simultaneously for 5 seconds (step 2 in above image.). This will activate the Monitor Diagnosis Mode (step 3 in 1.)
  2. Pressing AUTO again will switch to the Actuator Test Mode (step 4 in above image.).
  3. Pressing AUTO again will switch to the Upper and Lower Temperature Difference Adjustment Mode (step 5 in above image.).
  4. Pressing AUTO again will switch to a readout of Trouble Codes (step 6 in above image.).
  5. Pressing AUTO again loops back to Monitor Diagnosis Mode (step 3 in above image.).

Monitoring Diagnostics Mode

The control unit will display temperature data in this mode. The step monitor will have the right single dash lit (step 3 in above image.). Temperature data is returned in the display's 'Set' digits.

Use the Mode switch and the Fan switch to toggle through the menu items.
Def icon only
Ambient temperature
ºC(ºF)
Upper vent icon only
Upper cabin temperature
ºC(ºF)
Lower vent icon only
Lower cabin temperature
ºC(ºF)
0 Fan & Def icon
DEFROST outlet air temperature
ºC(ºF)
0 Fan & Upper vent icon
VENT outlet air temperature
ºC(ºF)
0 Fan & Lower vent icon
FOOT outlet air temperature
ºC(ºF)
1/4 Fan & Def icon
Sunload
*1
1/4 Fan & Upper vent icon
water temperature *3
ºC(ºF)
1/4 Fan & Lower vent icon
Mode door voltage *4
*2
1/2 Fan & Def icon
N/A

1/2 Fan & Upper vent icon
N/A

1/2 Fan & Lower vent icon
N/A

3/4 Fan & Def icon
N/A

3/4 Fan & Upper vent icon
N/A

3/4 Fan & Lower vent icon
N/A

Full fan & Upper vent icon
Difference in upper & lower temperatures
ºC(ºF)
Full fan & Lower vent icon
N/A

*1: One tenth of the value in kcal/h*m² unit
*2: Ten times the value in V
*3: When coolant temp. is below 40ºC(104ºF), indicates 20ºC (68ºF). When coolant temp. is above 40ºC(104ºF), indicates 80ºC (176ºF)
*4 Mode door voltage: 0 = VENT, 5 = DEFROST

Actuator Test Mode

The climate controller will force actuators to work in this mode. The step monitor should be the right two dashes lit (step 4 in 1.). The 'Set' digits in the display are the Mode door voltage, 0 = VENT, 5 = DEFROST. I'm not really sure what mine means with a 49 listed. Mode and fan speed can be set independently. When the upper and lower vent icon appears, a stabilized outlet temperature 30ºC(86ºF) is reached after the air mix door has be working for about a minute.
Use the Mode switch to toggle through the menu items.



Defrost icon
Defrost and lower vent icon
Upper and lower vent icon
Upper vent icon
Mode door
DEF
DEF/Lower
B/L
VENT
Intake door
FRE
FRE
50% FRE
REC
Air mix door
Full hot
Full hot
30ºC(86ºF)
Full cold
Compressor
OFF
OFF
ON
ON
operating condition of the actuators cannot be checked by indicators alone.
Use the Fan switch to toggle through the menu items.

Blower Motor
1/4 Fan
1/2 Fan
3/4 Fan
Full fan
Voltage
4V
6V
9V
12V

Upper & Lower Temperature Difference Mode

Adjustments can be made to the difference in upper and lower target temperatures in this mode. The step monitor should be 3 dashes (step 5 in 1.). The 'Set' digits in the display will show how much of a difference by 'data' numbers in relation to temperature difference.

Using the Fan and Mode switches to raise or lower the data number:
ºC spec.
Data
-20
to
-1
0
1
to
20
ºC spec.
Difference between upper and lower target temperatures
-2.0ºC
to
-0.1ºC
0
0.1ºC
to
2.0ºC
ºF spec.
Data
-36
to
-2
0
2
to
36
ºF spec.
Difference between upper and lower target temperatures
-3.6ºF
to
-0.2ºF
0
0.2ºF
to
3.6ºF
The programmed differences are stored until changed again, or the battery is disconnected.

Trouble Codes

The auto climate control stores error codes for later retrieval. The step monitor should be 2 dashes with a space in-between (step 6 in 1.). The 'Set' digits will show the number of ignition ON/OFF cycles since the problem was last detected. A dash '-' in the step monitor to the far left indicates a short circuit. A '|' hash in the step monitor on the left indicates an open circuit.

Use the Fan and Mode switches to raise or lower the code to change the desired data or status reading returned.
Code
Sensor
Open circuit
Short circuit
Defrost icon
Ambient sensor
Less than -70ºC(94ºF)
Greater than 141ºC(286ºF)
Upper vent icon
Cabin upper sensor
Less than -38ºC(-36ºF)
Greater than 141ºC(286ºF)
Lower vent icon
Cabin lower sensor
Less than -38ºC(-36ºF)
Greater than 141ºC(286ºF)
0 Fan & Def/lower vent icon*1
DEF duct sensor
Less than -38ºC(-36ºF)
Greater than 141ºC(286ºF)
0 Fan & Upper vent icon
VENT duct sensor
Less than -38ºC(-36ºF)
Greater than 141ºC(286ºF)
0 Fan & Upper/lower vent icon*2
Lower duct sensor
Less than -38ºC(-36ºF)
Greater than 141ºC(286ºF)
1/4 Fan and Def icon
Sunload sensor
Open circuit can not be detected w/ self diagnostic
Greater than 1.784kW (1,534kcal/h, 6,087BTU/h)/m²
[0.1657kW (142.51 kcal/h, 565.5 BTU/h)/sq ft.]
*1 One chart in the service manual shows 0 fan with Def/lower vent icon, while another shows 0 fan with Def icon alone.
*2 One chart in the service manual shows 0 fan with Upper/lower vent icon, while another shows 0 fan with Lower icon alone.

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