Rammer, which side did u block off, might have another crack! How did u block it?
Unfortunately i do not think Rammers fix will work for you. Without any vacuum reaching the controls, the valves that control direction default back to demist. A nice failsafe feature ford built into the system. Not sure what servo the garage is on about, on mine the pipe comes straight off the manifold. If i was you i might be tempted to just get hold of a length of similar vacuum pipe and run that up to your controls bypassing the problem bit altogether.