DIY Nissan climate control unit guide

by Staff | Last updated 25th April, 2016 | Posted in Guides

This is a detailed guide on how to diagnose problems with the Nissan 180sx and Nissan Silvia digital climate control unit.

Suitable applications for this guide:

  • – Nissan 180sx (jdm s13)
  • – Nissan Silvia (s14 jdm)


Please note that following this guide is entirely at your own risk. The 180sx Club is not responsible for any personal injury to you or to a third party and neither is it responsible for any damage done to your vehicle while attempting to follow this guide. The 180sx Club provide these workshop guides for experienced mechanics to use, if you are not confident that you have the correct skills then please take your vehicle to your favourite professional garage to complete the work.

Ok… From what I can gather, this is the same for S13 JDM unit, and for S14 (not S14a AFAIK, but possibly works the same also).
To “self diagnose” the Auto Temperature Controlled Air con/heating systems:

There are 6 stages of diagnosis…!

To enter stage/mode 1, the first point is to turn the ignition to ‘on’, and within 5 seconds of doing this, you press and hold the “OFF” button on the heater control unit, for 5 seconds…

The instructions are not 100% clear that it may need the engine to be started.
Although I doubt this is the case.

1st thing to happen should be that all the LEDs and display segments will illuminate… lots of 8’s I guess, unless its a starburst type = lots of stars!

If the elements don’t light up at this point, the off switch is malfunctioning… if some of the other lights/segments dont light up, then theres a problem with either some of the bulbs, or the fluorescent display tube.

If you then press the ‘up’ arrowed button (hot), the display should then read ‘2’, which indicates the 2nd stage of the diagnosis.

Pressing the ‘down’ arrow (cold) button will go from mode 2 – 1, and pressing the up arrow will go from mode 1 – 2.

Now unless the down arrow button isn’t working, you should see the number 2.
This is mode/stage 2.
You may then see the number 20 displayed, which means that all external sensors are working correctly.
You may find it reads number 21, 22, 25, or 26… this indicates a malfunctioning or incorrectly wired sensor.

The codes are:
20 = All ok.
21 = Ambient Sensor.
22 = In-Vehicle Sensor.
25 = Sunload Sensor.
26 = PBR (Air-mix Door Position Sensor)

Pressing the ‘up’ arrow (hot) button again will move to mode 3 = number 3 is displayed.

Mode 3 again, like mode 2, will throw up error codes (if any present) or code 30 = all ok.
Error codes in mode 3 are for checking all the intake door motor and mode door position switches for error/malfunction, these are the possible error codes:

Note: Codes 31-35 refer to ‘mode door’ motor positions.
Codes 36-39 refer to ‘Intake Door’ motor positions.

30 = All ok.
31 = Vent.
32 = B/L.
33 = Foot.
34 = Foot/Def.
35 = Def.
36 = Fre.
38 = 20% Fre.
39 = Rec.

So, if you’re happy its all ok, you can press the “up” arrowed (Hot) button again, and now will be on to mode/stage 4… Phew!

Stage 4 involves the Control Unit going through various test patterns… and TBH I haven’t a clue what help this actually is, but…
Either the unit will display “41” and perform test pattern 41, then follow on, through patterns 42-46 automatically…
Or the ‘Defrost’ button is used to cycle through each mode/pattern.
(For this test and mode/stage 5 diagnostics, the engine must be running, for the A/C compressor to operate… unless you don’t wish to test it).

Once you are happy with (or can’t be bothered anymore with) this modes function… press the ‘up’ arrowed (hot) button again, to enter the final stage of diagnosis… thank f**k!

So… Now the display should read ‘5’ = Stage/Mode 5, which tests the Ambient Temp and In-Vehicle Temp sensors.

Press the ‘DEF’ button, and the temperature reading from each sensor will be displayed… ‘DEF’ pressed 1 time = Ambient? then ‘DEF’ pressed again = In-Car Sensor?… or, the other way around..?!

Now hit the button with the fan displayed on it.

You should then see ’61’ on the display… this is the “Auxiliary Mechanism – Temperature Setting Trimmer” mode… and I’m guessing it calibrates the sensors for you.

Then hit either “Auto” button on the Unit, or turn the ignition to ‘Off’, and this will END the diagnostics mode! Finally.

So, to confirm… you can use the ‘Hot’ and ‘Cold’ arrowed buttons to scroll through the different modes/stages of diagnosis, and you can select any stage, at any time, when in diagnosis mode.

To ‘Exit’ diagnosis mode at any time, either press the ‘Auto’ button or turn the ignition to ‘Off’.

Gracious thanks to Nize from the SXOC for sharing this guide.