Internal Heater Problem, 2003 Gs430 Sport

eMJay · July 16, 2009

Recently I've noticed my internal heater is blowing slightly warm when set to the lowest 16 degrees Celsius setting whether it's on recirculation or external airflow, it was fine one morning and then like this in the afternoon, but I just put it down to the hot and humid weather making the internal components hotter than normal because the air con still works fine.

Today I noticed it is still running hotter than normal so changed the temperature one unit at a time and it stays at this warm temperature all the way until 25 and then gets hotter at 26 onwards and then is much hotter than I remember 30 being over winter.

Any ideas on what has happened?

Is there something I can check?

Am I looking at a new heater matrix? :(

Mike_B · July 16, 2009

From the way you've said that 'the aircon works' I assume you're testing with the aircon button set to off. Are you sure it's not just drawing external air in which is already fairly warm at this time of year? Mornings are usually a lot cooler than afternoons obviously, which could be why you've noticed it the way you have...

The temperature you see in the console is what it is trying to set the inside of the car to, which is not the same thing as the temperature of the air coming out the vents. If the car believes it is 20C inside the car, and you've set the temp to be 23C, then it will blow hot until the inside temp matches what you've set. If you set it to 16 and then turn the aircon off, there's not much it can do except blow in air from outside as quick as it can in an attempt to cool it down. But the air it blows out will be exactly the same temperature whether you've asked for 19C or 16C, if the outside air is already warmer than that.

I doubt it's the matrix at fault, because if you're asking for cool air then it will simply shut off hot water running through the matrix.

ColinBarber · July 16, 2009

The matrix sounds fine otherwise it wouldn't get hot.

If you set dual temperatures do both sides get hot? Sounds like the air mix motor isn't functioning correctly so some air is always being directed through the heater matrix

eMJay · July 21, 2009

Here's what I've noticed in the cooler weather: the heat it blows out is cooler than when the outside temperature is up, but it stays the same from 16 until 21-22 and then you can feel it blowing hotter. This is with the car's engine at normal operating temperature.

Is there anything I do to fix it or is it more severe?

TigerFish · July 23, 2009

on the mk1 GS's, the flow control valve for the heater matrix is located just above the rear end of the engine on the bulk head of the engine bay. There is a cable that connects to it with a clip. If that cable is unclipped or incorrectly adjusted, the heater behaves as you describe. i.e. it cannot close the valve fully, or cannot open the valve fully, depending on which way it is incorrectly adjusted. Is there a similar item on the later GS's?