Like so many people with this age of vehicle, many parts are no longer made. I need to know if anybody has either bypassed this dual sensor altogether, or found some aftermarket parts that can be adopted to work. Basically, my auto headlights do not work (which is not a big deal for me), and my heat is not as hot as I think it should be. I've replaced a bunch of the related parts, confirmed my blend doors are working, done a bunch of other crap, and have stumbled upon a few very old articles that mention if that sensor does not work, it will affect the HVAC system. For complete transparency, I have the OEM EATC system, and have not pulled it out yet to confirm there is adequate vacuum going to all lines. Key word is YET, lol, but regardless, I want to eliminate that sensor as an issue.

 

I may be able to help with eliminating that sensor as an issue. The auto headlights in my 2003 have not worked for years - they stay on if it's light out or not - and my heat has always been hot.

I would first check that the coolant heater valve is operating correctly - gets vacuum and fully opens. If it does, then I'd pull the supply and return coolant lines and make sure the heater core isn't clogged up. I'd probably try to flush it in reverse to push out any debris or gunk that has built up over time.

 

My 99 doesn't technically have a "heater valve". Everything is controlled through the EATC module. Like I said, I have not pulled that out yet to verify adequate vacuum to all the lines yet. It's been to cold to mess with it, but I assume there is adequate vacuum coming in because my AC works VERY well. To me, that also likely eliminates the blend door....but at some point, I'm planning to cut a hole in the core box to check it. Either way, I have a set of new seals for the EATC module that will be replaced when it gets pulled out to check it. The blend door, heater core, and a bunch of other parts in there were replaced about 10yrs ago. I also flush the system and back flush both heater cores about every 3 yrs or so. The last flush was this past summer.

I'll have to see if I can find some of the forums that mentioned the sun load sensor being the issue with their HVAC. It was quite a few, but most of them were at least 10yrs old. None of them mentioned anyway to bypass the sensor because there were replacement sensors available at the time.......not anymore. Like I said, at the end of the day, I couldn't care less if the auto headlight feature works, but I would like to be able to replace the sun load sensor part of it.