Aircon blowing hot and cold - mab23


Have a 4 year old Merc A class A170 diesel, which has just recently started to blow hot and cold with the aircon on. Sometimes when set to its coldest setting it blows very cold (like it should) for a while, then it might blow hot (not just room temperature, hot) for a while (anything from 5 minutes upwards), then maybe back to cold again. Sometimes it will blow hot from starting.

Does anyone have any ideas as to areas to look at as to the cause of the problem? I think it may be a loose wire somewhere, if it were gas issues shurely it wouldn't work at all?

The Merc garage had a look but say they couldn't find anything wrong, I reckon they just started the car and because it worked for them at that point they ignored the issue...

Any advice appreciated...


Aircon blowing hot and cold - SkyMan
Hi Mike,

If its got climate control, then I'd say the cabin temp sensor is playing up - e.g. it sometimes maybe goes open circuit so the climate control thinks the car is really cold, and therefore gives a blast of heat to bring it up to the temp selected, before keeping it at that level.

If its not climate controlled, then sorry - no idea!

Aircon blowing hot and cold - Marcos{P}
I think these have semi-climate control so you set the temp and it will blow hot or cold depending on the temp inside the car. I would tend to agree with skyman that it is probably a fault with the internal temp sensor.
Aircon blowing hot and cold - mab23

Although it has temperature markings on the aircon dial (from 28 (deg C I guess?) at high to 16 deg C at low), I don't think it has climate control...

When the aircon used to work properly, if you set the temperature dial to full cold it would blow full cold, all the time, even in the depths of winter (as I would turn the aircon on full once a week or so just to keep the seals from drying out).

Any other ideas...?

Aircon blowing hot and cold - Aprilia
As has been said, this is a simple form of climate control. When you set the dial to 20 deg. C. there is a control system that monitors the cabin temperature and controls it accordingly to achieve the 20 deg. C set point (by feeding in hot/cold air, as appropriate).
There is a fault with the control system - either the sensor(s) or control unit. You need MB to run a diagnostic tester over it (and a healthy bank balance.....).
Aircon blowing hot and cold - mab23
Thanks, will empty my wallet in the general direction of Mercedes.

Unless anyone wants to buy a PoS A-Class with dodgy aircon... :-)


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