P38 Heater problemette...

Hi Guys,

I know I've seen this raised somewhere before but I'm buggered if I can find it now.

Noticed the other day that I can't get any hot air out of my hevac unless I set the temp controls to HI at which point the air is roasting hot. It seems to be ambient temperature the rest of the time unless I put the aircon on which is then freezing cold (unless temp is set to HI).

Is this likely to be the matrix temperature sensor? Or the cabin air temp sensor? Doesn't sound like a blend issue to me, but I spose it might be... No book symbol on the display and air distribution seems to work ok.

Probly ought to get this sorted before it gets too cold as HI is just too hot for comfort.

Guy

Firstly, if you don't have one in your garage..go to a local garage with an airline and give the small vent just below the clock a blast or two. The cabin temp. sensor which consists of a very small fan with a sensor in front can get clogged with dust and fluff. The fan draws air over the sensor and if it gets clogged, it can't run properly.
Hold a cigarette lighter or a cigarette if you are a smoker, in front of the grille, you should see the flame or smoke drawn towards the vent..do this with the engine running and the heating on "Auto". If you select say 24 deg., the blower fans speed should increase and the air temperature from the vents should automatically get cooler to compensate for what the system thinks is a high cabin temperature. Likewise, the solar sensor on the dash should act the same if a bright torch is shone directly at it.
The heater core and other sensors can be quickly and easily checked with diagnostics, takes all of 5 minutes to do.

Hi Irish,

Tried the cigarette lighter thing - no movement at all so I assume the fan on the sensor is not working - I'll try blowing it out.

I did notice on Auto, that the fans speed up if I increase or decrease the temperature on the hevac, but the actual temperature of the air coming out doesn't seem to change until I get all the way to HI. Which sensor is it that controls the fan speed, the one above the stereo?

It seems like whatever controls the temperature of the air coming in isn't working.

Not sure if this is relevant, but I have noticed in the past that when I'm slowing down, the air coming out of the vents seems to get hotter all of a sudden....

Diagnostics - all of 5 minutes and £50 each time! Thieving indies.

Guy

The blower speed when the HEVAC is in "Auto" is controlled by the HEVAC itself. Obviously if the car is red hot inside and the set temperature is much lower, the HEVAC increases the blower speed to cool it down as quickly as possible. If however the temperature difference is small then the blowers operate at low speed.
There could be a problem with the sensor fitted into the heater box. It's located at the passenger side, you will have to remove the panel below the glove box or maybe the glove box itself to get at it.
Problem with replacing sensors at random is that it can work out more expensive that the cost of a diagnostic check.
If someone bought the car to me and wanted a check like that, it would cost a packet of fags !!!

Irishrover said:

The blower speed when the HEVAC is in "Auto" is controlled by the HEVAC itself. Obviously if the car is red hot inside and the set temperature is much lower, the HEVAC increases the blower speed to cool it down as quickly as possible. If however the temperature difference is small then the blowers operate at low speed.

Click to expand...

Ok, but what controls the temperature of the incoming air? It seems to be that which is causing the problemette.

Does it show the correct outside temperature?

Datatek said:

Does it show the correct outside temperature?

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Hi Keith,

Yes, it seems to.

kooky_guy said:

Hi Keith,

Yes, it seems to.

Click to expand...

Then I agree with Irishrover, the little fan is gummed up in the cabin sensor.

Datatek said:

Then I agree with Irishrover, the little fan is gummed up in the cabin sensor.

Click to expand...

Bleeding thing was working fine this morning! Nice and warm.