Volvo Repair: 1986 Volvo 244 GL, temperature control valve, volvo 244

Question
The heater can not be turned off. That is, the tempurature lever set at zero has no effect, the fan still blows hot air.
I have checked to see that lever to temperature control valve linkage is not loose or slipping and is infact setting the valve to the fully off position.
   My conclusion is that the temp. control valve has failed.
   My question is, can the valve be removed and replaced without removing the heater housing and if not, what is the best approach to heater removal? Do I need to drain the coolant from the engine? Thanks for your attention.

Answer
Lionel, see, you didnt need me, you diagnosed it yourself.  Draining the coolant is advisable as well as taking the top hose off in the engine bay and use compressed air to remove any coolant from the heater core, etc.  When you take the valve off from the inside, it will make a mess so towels should be placed down.  If you have any other questions, let me know.  Roger