HVAC always hot on one side, cold on the other

[MikkiJayne]

Hi all,

Since I've had it, my D2 has always blown hot from the driver's side vents and cold from the passenger side. The centre vent always blows cold. The temperature setting on the HVAC is pretty much irrelevant, as is the control in the centre vent, so I set the cabin temperature by balancing airflow through the vents. Like a Land Rover...

I think this is all down to erroneous readings from the two vent temperature senders G150 and G151 which are in outlets of the air box. The left hand reading climbs steadily from ambient to >65 over the course of a few minutes as soon as the ignition is switched on (the engine doesn't have to be running!). The right hand reading lags significantly below coolant temperature, generally going from ambient (7 today) up to a maximum of about 17. I have replaced both sensors with new ones but they still have no bearing on the actual air temp. The HVAC controller responds to the erroneous readings exactly as you would expect if they were real readings - no heat on the passenger side trying to cool it down, max heat on the driver's side trying to heat it up.

Curiously, the coolant temperature value shows 30, at an ambient of 7 which is peculiar. This is sent to the HVAC controller by the instrument cluster, and once the engine was on it tracked within a couple of degrees of what the ECU said so its odd, but I don't think its a problem.

All the flap motors have calibrated fine, show plausible basic settings values, and respond to output tests so the only thing I can think of now is to replace the HVAC controller?

Anyone seen anything like this before or have any other suggestions?

Thanks