Running cold when in car heater is on

[Roberts1408]

Just noticed that when the ac heating is on the car is running around 50degrees and does not warm up until heating is turned off.

 

[Flanners]

Other cars that have done that over the year's have meant that the thermostat has failed.

 

[Roberts1408]

In previous cars that would be my first but this has the clutched coolant pump but don’t realy know what parameter controls the clutch on it??
I will have a look at the thermostat first if it’s easy to get to