An Odd Car Heater Question

I’ve just picked up a 2003 Toyota Highlander V6 AWD (I think these were available in the UK, although the vehicle itself probably doesn’t matter too much).

The aircon works fine.

The heater blows cold air with the air con off.

The heater blows hot air fine with the air con off.

But!

Instead of slowly transitioning between cold, warm and hot air, with the rotary heat control dial fully anti-clockwise the air is cold, yet turn two clicks clockwise (out of maybe 20 clicks but not counted….) and the air immediately becomes full hot. No slightly warmer, then a bit more warm etc as you turn the dial clockwise. Just cold then hot! I’ve never come across this before and even the Google Machine isn’t helping.

It’s not a huge deal but I’m curious nonetheless.

My van sometimes does this.

Do you have climate control (adjusts fan and temp to maintain a set temp) or dumb air con?

Mine is climate and I suspect the cab temp sensor is duff, my heat gradient is fine but cold aircon is either full wack or ambient temp, no real gradient in between.

If it’s dumb controls, I’m guessing here but your hot air flap that controls air through the heater core may be stuck open. So as soon as you ask for a tiny bit of heat, hot coolant goes to the heater core but you’ve already got all the blower air coming through the heater core rather than just a fraction.

Dodgy blend motor as mentioned above. Take the dash out Molgrips style.

2 weeks and 10pages on here I reckon as the blend motor will be the first thing they start with in the Toyota factory when building the car.

A friend had one of his works drivers pick him up one cold and winter morning in the van.

The driver had a cooking pot full of meths alight in the passenger foot well.

Thanks for the help. I thought the blend motor door was some kind of in-joke until I looked it up! Yes it’s dumb air con, not climate control. Looks like a problem to ignore for a while at least, as I still have hot, cold, very cold and windows.