Issue with climate control

My disco has climate control and it doesn't seem to blow warm. Today the outside temperature was 9 degrees and the inside set at 20 but the climate control was blowing as cold.

Also last week it was warm outside and the inside temperature was set to 18 which cooled the car but the air con kept blowing cold and it got so cold in the car that I had to turn the air con off. Increasing the temperature control didn't seem to do anything.

Is there anything I can check or is checking the air con a specialist job?

run this procedure then come back if no outcome

Thank you SF but ran the diagnostics and came back 00. Any more suggestions?

did you bleed well the system? with warm engine check the two pipes near the bulkhead which are feeding the heater matrix... they must be evenly warm.... if they're not it could be an airlock or the matrix is clogged... if they are both warm it means that the flap which must direct the air through the matrix id blocked closed andf you have to get to the mechanism...which is a pig of a job

did you bleed well the system?