1986 740 Temperature Control

I have a 740 with no heat. This past weekend I dissembled the console
enough to remove a radio a prior owner had installed, I also took this
opportunity to examine the slider control which goes from cold (left)
to warm (right) to see why it has no apparent effect.

The slider rotates an arm through an arc of perhaps 30 degrees, to the
cold direction the last few degrees slide a cam on a vacuum switch,
but other than that there's no apparent connection to anything else,
i.e. a cable, rheostat or variable vacuum control. To the rear and
bottom of the assembly there is a spot which looks like something had
been mounted and removed. On the arm is a worn protrusion about 1/4
the way in from the side which looks like a cam may have been there
and broken off.

I would appreciate at least a photo of what a normal functioning unit
looks like on the bottom side as I expect a previous owner removed
something here.

I've looked about for vacuum tubes, wires or cables which appear
unconnected in the vicinity and haven't spotted anything which has
placed me at wits end. Cooler days are coming and I'd very much like
to get the heating working.

Thanks for any help!

 

While I don't have a pic of the control handy, I can tell you that the
heater valve is vacuum operated and located under the hood near the
firewall. In a pinch you could connect it to a different source of vacuum to
get you by for a while.

 

Thanks for the help, mate. I've inspected under the bonnet and found
the vacuum tube which runs from near the firewall (a vacuum relay?) to
the heater valve, which appears to have worn through by friction with
the throttle cable. Sod it. Now to ponder how I can go about
patching this thing or replacing it.

Me mate, Colin is a genius with Volvo's so I'll give him a shout.