# B15 Defrost Modification



## cademetz (Apr 29, 2003)

I hate that the compressor doesn't turn off once the selector has been pushed over to defrost, and remember reading a "How To" to modify the controls so the compressor won't come on when turning it to defrost. However, I have searched and searched, to no avail. Any help?


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## Black V (Mar 14, 2004)

cademetz said:


> I hate that the compressor doesn't turn off once the selector has been pushed over to defrost, and remember reading a "How To" to modify the controls so the compressor won't come on when turning it to defrost. However, I have searched and searched, to no avail. Any help?


Go here:

http://www.b15sentra.net/forums/showthread.php?s=&threadid=58147&highlight=defrost+mod

Read the first post ONLY. It has everything you need to know. BTW, I did this. Fairly easy to do and I'm happy w/the results. I chose to bend the tab on the microswitch, which seemed to be the easiest thing to do (don't have to unscrew/unmount the switch). It's reversible that way, too. :thumbup:


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## davejay (Feb 20, 2004)

*Summary of that thread*

So the thread linked above is a long and painful one. Here's a summary:

All 2003+ Sentras have a climate control system that, like earlier Sentras, turns on the A/C automatically when you select a defrost position and a fan speed. Unfortunately, unlike earlier Sentras, the A/C will STAY ON, even if you select a non-defrost position, until the car is shut off. Turning off the fan will stop the A/C, but until the car is shut off, the A/C will start up again as soon as you select a fan speed.

This is really, really annoying. My dealer's service guy said "this is normal" (which turns out to be true) but the mechanic said "something might be stuck" and ordered a part. It's discouraging to learn that, whatever part he ordered, it's not going to change the A/C behavior. 

For what it's worth, this behavior is very annoying to me because the climate control knob is very vague, and I occasionally overshoot the non-defrost setting and hit the first defrost setting for just a moment -- enough to turn the A/C on. Also, I occasionally need the defroster, but since I'm in Southern California, I only need it for a few minutes and it's annoying to burn extra gas by running A/C I don't need with the heater turned up so I'm not cold (yes, it gets chilly in socal. Heh.)

If you follow the link in the post above, you will see a modification that prevents the A/C from turning on automatically when you select a defrost position. If you want the A/C to run while you're using the defroster, you'll still be able to turn it on by pressing the A/C button manually.

To help avoid confusion, here's a summary of pre-2003 and 2003+ Sentra climate control behaviors.

Prior to 2003, Sentra climate control worked as follows:

- In all positions, if fan is set to 0, A/C cannot be turned on.

- In non-defrost positions, if fan is not set to 0, A/C can be turned on and off manually by pressing the A/C button.

- In defrost positions, if fan is not set to 0, A/C will turn on automatically, and will turn off if a non-defrost position is selected (or the fan is turned off).

In 2003, Nissan changed their ECU programming as follows:

- In defrost positions, if fan is not set to 0, A/C will turn on automatically, and will NOT turn off unless the car is shut off, or the fan is turned off -- and if the fan is turned on again (before the car has been shut off), the A/C comes back on.

I hope this saves some of you the pain of reading through 7+ pages of forum posts to get the same info -- you can just read the first post to see how the mod is done.


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## GarrettSER (Apr 6, 2003)

davejay said:


> So the thread linked above is a long and painful one. Here's a summary:
> 
> All 2003+ Sentras have a climate control system that, like earlier Sentras, turns on the A/C automatically when you select a defrost position and a fan speed. Unfortunately, unlike earlier Sentras, the A/C will STAY ON, even if you select a non-defrost position, until the car is shut off. Turning off the fan will stop the A/C, but until the car is shut off, the A/C will start up again as soon as you select a fan speed.
> 
> ...


Does anyone know why the hell Nissan designed it to do this? What a stupid design. Is there any logic, or is it a glitch that will never be recalled because it isn't a safety issue?


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