Clock? Heater resistor?

I have a 1994 4 litre air con works fine so does the blower ,but when I turn to heater it still blows out cold air any ideas

Glove Box lock barrel broken, can't find replacement

I had this problem with my 93 facelift model it gradually got worse until the only way to get the fan to work at all was to leave it switched to low permanently, turned out to be a transistor and diode faulty on both fan control boards. David Marks 0115 982 2808 is an expert on this problem.