It;s a problem with the control unit - I have well documented issues with aircon & non-running fans + overheat alarms going off all the time & last weekend bit the bullet - discovered both aircon & cooling fans had failed --- fitted a couple of spares & have the same problem as you - bit the bullet, decided the aircon would not work again so fitted a 'kenlowe' type separate thermostat - problem (at least for the cooling sorted for £24)