Hi John,I am not sure on your model but sometimes they are incorporated into the heater pipes,you should see the pipes going through the bulkhead from the engine to your heater matrix,have a look at them,most are electrically operated now but yours is quite an old car and may have cables,it may be seized/corroded,if your heater control knob has wiring to it then you know it is electric.If Nigel is looking then he may have a fault finding guide he can e mail to you.good luck.
cdc
July 2012