Blowing hot air when it not suppose to

[Bender]

Got this problem from the day when i bought the car. When temp is set all the way down to 18° it blowing cold air but as soon i set temp for 19° or higher it act like it was set for max temp 32° so i only got two choices when driving cold or hot nothing between. I was thinking that hvac unit was Faulty but i had spare one and I change it and it still working the same. Any idea what it can be? 

[Style]

My car does this too and I've never really bothered trying to track down the cause as I'm terrified it'll be the heater matrix. Not a small job and all replacements seem to be pretty rubbish

[TRD-1]

Not sure if this helps, but I had a similar issue with a Celica, and it turned out that the Interior temperature sensor wasn't connected so the climate control unit wasn't getting a interior temp signal.

I don't know where the interior temp sensor is on a Supra but might be worth checking if its connected or gone faulty.

[Ric]

The interior temp sensor is behind the little 1cmx1cm grill above the cigarette lighter.

[Bender]

So it could be fault of that interior temp sensor? 

[Swampy442]

14 hours ago, Style said:

My car does this too and I've never really bothered trying to track down the cause as I'm terrified it'll be the heater matrix. Not a small job and all replacements seem to be pretty rubbish

Its not heater matrix as a) its not leaking and b) youre getting heat

[Bender]

9 hours ago, Swampy442 said:

Its not heater matrix as a) its not leaking and b) youre getting heat

Thats what i was thinking. I guess it will be some small thing... 

[Ric]

The only other thing will be the flaps inside the heater box. Perhaps it's not rerouting the air away from the heat exchanger.

I remember an old thread where somebody had heater issues and a little arm which controlled the flaps had come off under neath the glove box. Worth a check for nothing.

Thinking about it, i expect the temp sensor only comes into play when it's in AUTO it shouldn't matter if you just set cool and leave it there. really.

[Style]

45 minutes ago, Ric said:

The only other thing will be the flaps inside the heater box. Perhaps it's not rerouting the air away from the heat exchanger.

I remember an old thread where somebody had heater issues and a little arm which controlled the flaps had come off under neath the glove box. Worth a check for nothing.

Thinking about it, i expect the temp sensor only comes into play when it's in AUTO it shouldn't matter if you just set cool and leave it there. really.

I'll check those things out on mine, thanks. I just find it weird that it literally goes from coldest at the lowest setting to as hot as possible one click up. Never really bothered me too much but always good to get to the bottom of it

[Bender]

9 hours ago, Ric said:

The only other thing will be the flaps inside the heater box. Perhaps it's not rerouting the air away from the heat exchanger.

I remember an old thread where somebody had heater issues and a little arm which controlled the flaps had come off under neath the glove box. Worth a check for nothing.

Thinking about it, i expect the temp sensor only comes into play when it's in AUTO it shouldn't matter if you just set cool and leave it there. really.

Thanks for idea will have a look on that

[Bender]

I check for faults https://www.supraforums.com/threads/hvac-diagnostic-system-check.523885/

And that was my hvac comes with

 

[m12aak]

As @TRD-1 mentioned, I think there's something wrong with your interior temp sensor, as the face flashing is a fault with the room temperature circuit, which is behind the little grille to the top right of your 12v socket as @Ric said. The service manual says it should be 1.6-1.8k of resistance at 25c. The defrost/heater one isn't an issue as that's the solar sensor, but your fresh air light flashing indicates that you did (and maybe still do) have low A/C refrigerant. I'd look at the interior temp sensor first though. 

[Nathanj1142]

I had this issue last year, it turned out that the big block cable behind the heater controls wasnt quite plugged in right, give it a wiggle and check there aren’t any wires that are loose, it’s possible one of the crimps have snapped if someone’s been installing an aftermarket stereo or something 

[Bender]

Thanks @m12aak and @Nathanj1142 will have to take dash out and check everything 

[Bender]

UPDATE

Problem fixed took the dash off today and find out interior temp sensor wasnt been connected. Put the plug back clear errors on hvac and everything work as it should. Once again thanks to everybody 

[Ric]

13 hours ago, Bender said:

UPDATE

Problem fixed took the dash off today and find out interior temp sensor wasnt been connected. Put the plug back clear errors on hvac and everything work as it should. Once again thanks to everybody 

Great news. Had to be something simple.

[Style]

Good stuff. I still need to check mine but very promising to know that it's something simple