Warning - This is a risky mod. Not recommended if you're not confident in electronic work. Do so at your own risk.

I have a '99 w/ digital climate control. Procedure should be similar for older models w/ digital climate control.

My reasons for doing this mod:
During the cold I usually set HVAC to the floor or vent before shutting off the car (prep for remote start).
I don't want the front defroster on if it has been snowing as it melts the snow onto the windshield and makes a mess before I can come and brush it off.
But when there's no snow and only frost, I wish the defroster was on to clear my windshield before I get in the car.

This mod allows me to remotely "push" my front defrost button using my remote starter's AUX channel.

Here's a video demonstration.

I used a 12V mini circuit board relay since it's nice and small compared to standard automotive relay. It's rated at 10 amps, more than enough for this project.



Disassemble the climate control housing.



Separate the front circuit board from the rest of the assembly.
As you can see, rubber membrane style buttons are used instead of mechanical switches. This will make things a little tricky for soldering the connections.



The traces are way too close to each other at/near the button itself, so we must move a little bit away from it (follow the traces).
The pic shows the best place I found to connect the wires.
Be very careful when scraping the solder mask (use a new razor with no rough spots or gouges). Don't scrape the actual copper!



Tin the wires with solder first. Use some helping hands to prevent the wires from moving. Don't use your hands, the wire should not move at all while the solder is cooling.



Wires routed from below.



Small hole drilled in the plastic to pass the wires through.



Here are the relay connections.



I used a mini connector for quick disconnect, making the removal of the HVAC easy as before for any servicing. Hot glue was used to secure everything.




BTW, rear defrost is easy. Connect one of the (-) AUX outputs from the remote starter to the green/red wire at the rear defroster switch.

 

How do you embed videos? I don't see an option in the thread editing toolbar. The code doesn't see to work.
Edit - Woops, looks like all I needed was to paste the link...

 

That's pretty awesome. Nice write up too.

Sticky!!

 

I don't get it?

Weather report lets me know what setting to use, and why not melt the snow?

A better mod would be for the rear and side view mirror defrost button.

My .02

 

It's for picky people like me, let me explain.

Weather reports are great, but looking out the window tells me if there is frost on my windshield or not.
Another example, there may be a forecast for 20% chance of snow, but it may not happen over my area. I don't want the A/C compressor running w/ the defroster unnecessarily (that's just me).
Plus, the defroster mode doesn't warm up the cabin as well as the other settings do...

As to why not melt the snow? It's fine when it's mild, it will all melt and is easy for the wipers to clean it.
But, when it's -30C to -40C (-23F to -40F) outside, a warmed up car will not melt the snow off the entire windshield. The little bit that does melt is then smeared onto the rest of the windshield when you go to wipe it off. Then you have to use the scraper to clean it.
In that case I don't want to enable the defrosters...

Rear defogger is easy, I've mentioned it towards the end of the 1st post.
BTW, I also have the windshield wipers hooked up remotely too, it lets me wipe the snow before getting in.

I have a video of the operation.