So my Highlander has been blowing out about 10 degrees hotter on my driver side. I know the 2003 Highlanders have AC module issues with the blend knob soddering joints coming undone. I decided to take that knob out completely since it was broken and remove the blend door actuator on the passenger side behind the glove box. And just just leave it on the max cool position. While the passenger side remains to blow cold the driver side is still blowing hot. ( There is no leak in the Freon and my pressures are at a good level)
Can confirm, 2008 had identical symptoms and fix.
Sounds like a blocked heater core. I recommend doing a flush to help loosen junk from heater core. Then flush completely out with distilled water and refill with toyota coolant. If that doesn't work then you might have to have heater core replaced, which is expensive and time consuming. Check out carcarenut guy channel for diy and questions all about toyota. Good luck keep us posted. Godbless
The heat works fine it’s AC That’s warmer on the driver side.
My apologies read it wrong! Could be one of the various actuators. Check out this link and diagnose which one.
I can only find the one actuator on the passenger side. Do you know of any others?
Could also be the dampner
https://autoparts.toyota.com/products/product/servo-sub-assy-damp-8710633260
Just look at the diagram should show the actuators and other parts of the cooling and heating system. Hope this helps
Not sure if this applies to the 2003 but the 2015 has issues where the A/C refrigerant reads normal but is actually low. Went nuts last year trying to diagnose - ended up recharging the refrigerant despite testing normal and it fixed the issue immediately. Symptoms were the same - passenger side was still cold - driver warm.