Auto climate control temp wanders

I have a 97 max with the auto climate control; here are the diagnostic procedures from the 97 service manual.

Turn Ignition from off to on,

Within 5 seconds press and hold the off button for 5 seconds.

You can now cycle through each dignostic mode by using the up/down temp selection buttons. For steps 4 and 5, engine must be running for compressor to operate. The modes are as follows:

1. LEDs and segments are checked.

1. Input signals from each sensor are checked.

2. Mode and intake door motor position switch is checked.

1. Actuators are checked.

2. Temperature detected by each sensor is checked. Multiplex communication errors are checked.

1. AUXILIARY MECHANISM Temperature setting trimmer.

Step 2: check the sensors. The code will be shown on the climate control display. You should perform these tests under sunshine at normal engine operating temperature. And now for the codes:

20 All sensors are functioning properly

21 Ambient Sensor

22 In Vehicle sensor

23 Thermal transmitter (Thermister) *If engine coolant is low, code 23 may appear even if this sensor is functioning.

25 Sunload sensor *When conducting this test indoors, direct light (more than 60w) at sunload sensor (Code 25) will indicate malfunction even if the sensor is functioning propery.

26 PBR

Step 3: check the intake and door switches. Malfunctioning switch codes:

Mode Door Motor

30 No fault 31 Vent 32 B/L 33 Foot 34 Foot/DEF 35 DEF

Intake Door Motor

36 FRE 38 20% FRE 39 REC

Step 4: check actuators. Press DEF to change test pattern. Nissan has a grid printed in the book. Here is a rough approximation:

| Mode | Intake | MIX | Bi-Level | | Code# | Door | Door | Door | Door | Blower | Compressor

------------------------------------------------------------------- 41 Vent REC Full Cold Open 4-5V ON 42 B/L REC Full Cold Open 9-11V ON 43 B/L 20% FRE Full Hot Close 7-9V OFF 44 Foot FRE Full Hot Close 7-9V OFF 45 F/D FRE Full Hot CLOSE 7-9V ON 46 DEF FRE Full Hot CLOSE 10-12V ON

Step 5: Display temperature detected by each sensor:

Use DEF to select sensor, Ambient or In-vehicle sensor.

There's about 40 pages on servicing the climate control. I only typed up the four page summary section. Hope it proves useful, although it would be really funny if Nissan had changed the climate control units enough so that this info was useless and the last half-hour I spent typing was wasted...

Aaron

Thanks! Hopefully others will search it out in the future and get some use too.

I haven't tried this yet but I am pretty sure the problem has to be sensor related. I no longer believe the problem could be related to the coolant control valve -- if the flow was too high or too low, I think the fan speed would adjust to try to compensate.

Instead, the fan speed seems to be the biggest problem, because the speed just stays the same, even at start-up when cabin temp is very low. (There used to be an automatic blast of hot air after a couple of minutes of warm-up.) Instead, I have to nudge the fan up, along with the temp setting, to get it to heat seriously, and then it heats up very fast. (Then gets too hot.) Yesterday was the worst operation ever, so this is not just going to go away.

JM

The book says that the follwing items could be a cause:

Mode Door Blower Motor Engine Cooling system Coolant level Hoses, kinks or leaks Radiator Cap Air in cooling system Air Mix Door Ducts, Leaks, blockages, etc

I would guess that the coolant level is low or there's air in the system. You could also have something blocking the air mix door... It was probably a bad idea to let the kids put crayons in the vents, but hindsight is always 20/20.

Aaron

One last thought, the thermistor could probably cause your troubles too.

Aaron

If it isn't heating up, I can force it to, by turning the heat to 85 and the fan all the way up. The system does put out massive heat that way. I'm sure the problem is electronic and not mechanical.

When I put it into diagnostic mode, it appears that the ambient air and the inside temps are about the same -- even when they are not anywhere near the same. The coolant thermistor checks out fine: "bad" when the coolant is cold and "ok" when it is hot, just as it should. Sun sensor is ok too.

So, I am drawn to the conclusion that one of the air temp sensors is bad or a air sampling hose has slipped off it, which was mentioned in another thread on this board. What I don't understand is, some days it works almost correctly, and others it is completely goofy. If it is merely a air sampling hose that came off, then it should be off and stay off. Therefore, I think the problem is in the electronics.

Thanks again,

JM

I guess the question is.... which sensor seems accurate? The other is where you should start looking.

Aaron