The following applies only to the Phase 1 vehicles:
My Phase 1 had the same problem (blowing hot air even when set to cold) when I bought it. I solved it by adjusting the "length" of the outer sleeve of the cable. This involves the removal of the centre console. So first try to diagnose the cause of the problem.
Locate the water valve next to the heater matrix. Look for it to the center of the left hand foot well. You can see the valve opening and closing as you turn the hot/cold dial. With the dial on "cold", try to move the lever on the valve slightly more towards the closed position (taking up the slack in the cable). If that makes the difference between getting hot air and "outside temperature" air, the problem is in the length of the cable. I adjusted the length of the cable outer by turning the fitting that clasps the outer sleeve a few turns. Mine was fixed by a very small adjustment - about 3mm.
Time-consuming, but worth it.